Acta agriculturae Slovenica, 121/2, 1–23, Ljubljana 2025 doi:10.14720/aas.2025.121.2.20051 Original research article / izvirni znanstveni članek Identifying gene actions to rice yield and its components traits under both normal and drought conditions Mahmoud GABALLAH 1, 2, Amgad ELGAMMAAL 3, Nabil ELSHEERY 3, Mohamed GHAZY 1, Raghda SAKRAN 1, Hasnaa MAHROSE 3 Received October 26, 2024, accepted April 26, 2025 Delo je prispelo 6. oktober 2024, sprejeto 26. april 2025 1 Rice research department, Field Crops Research Institute, Agricultural Research Center, 33717, Sakha, Kafr Elsheikh, Egypt 2 Corresponding author (mahmoudgab@yahoo.com) 3 Agronomy Department, Faculty of agriculture, Tanta University Identifying gene actions to rice yield and its components traits under both normal and drought conditions Abstract: Eight rice genotypes were selected to conduct all crosses in diallel Method 2 Model 1 design to generate geno- types tolerance to drought stress with high yield potential. The parents Giza179 and Sakha 108 and the crosses UYR 3472 × GZ10739 and GZ10487 × Giza179 reported the highest mean values of the grain yield plant-1 under drought conditions. Two and twelve hybrids revealed desirable highly and highly signifi- cant positive heterotic effects as a deviation over mid parent, one hybrid obtained significant positive heterotic over better- parent under natural condition. Regarding the grain yield plant-1, four and six parents showed desirable significant and highly significant positive general combing ability effects under either natural and drought conditions, respectively. Five and thirteen hybrids showed desirable significant and highly sig- nificant positive specific combining ability effects under both natural and drought conditions, respectively regarding grain yield plant-1. The high significant and positive associated among grain yield and days to heading, relative water content, num- ber of panicles plant-1, thousand grain mass and water use effi- ciency for both natural and drought environments. The crosses GZ10739 × WAB 638-1, GZ10739 × IRAT112 and WAB 638-1 × IRAT 112 had superior in most agronomic traits at drought condition. Key words: combing ability, heterosis, heatmap, correla- tion, drought Določanje delovanja genov, ki vplivajo na pridelek riža in nje- gove komponente v normalnih in sušnih razmerah Izvleček: Izbranih je bilo osem genotipov riža za izved- bo dialelnih križanj (Metoda 2 Model 1) za vzgojo genotipov s toleranco na sušo in velikim potencialom pridelka. Križanci starševskih genotipov Giza179 in Sakha 108 in križanci UYR 3472 × GZ10739 ter GZ10487 × Giza179 so imeli največji poprečni pridelek zrnja na rastlino v razmerah suše. Dva in dvanajst križancev je imelo zaželjen velik, značilen pozitivni heterotični učinek kot odklon od poprečja staršev, eden od križancev je v naravnih razmerah dosegel značilno pozitiven heterotični učinek glede na boljšega starša. Glede na pridelek zrnja na rastlino so štiri in šest staršev pokazali zaželjene značilne, pozitivne, splošne kombinacijske učinke v nara- vnih razmerah kot v razmerah suše. Pet in trinajst križancev je v naravnih in sušnih razmerah pokazalo zaželjene in visoko značilne pozitivne specifične kombinacijske učinke glede na pridelek zrnja na rastlino. Ugotovljena je bila zelo značilna in pozitivna povezava med pridelkom zrnja, dnevi do klasenja, relativno vsebnostjo vode, številom latov na rastlino, maso tisočih zrn in učinkovitostjo izrabe vode v normalnem in sušnem okolju. Križanja GZ10739 × WAB 638-1, GZ10739 × IRAT112 in WAB 638-1 × IRAT 112 so bila superiorna v vseh agronomskih lastnostih v razmerah suše. Ključne besede: sposobnost kombinacije, heteroza, dvodimezionalna barvna predstavitev podatkov, korelacija, suša Acta agriculturae Slovenica, 121/2 – 20252 M. GABALLAH et al. 1 INTRODUCTION Rice (Oryza sativa L.) is one of the most important agriculture food crops for more than half of the world population. Moreover, it is a very important cereal crop in Egypt for both consumption and export (Zheng et al., 2020)breeders manually perform extensive testing of hy- bridizations between restorer and sterile lines, which is a laborious and time-consuming process. Here, we report that a modified flowering stimulant containing methyl jasmonate (MeJA. Egypt is facing two major challenges, food security and water shortage, particularly in the ter- minal areas. Water shortage is one of the most limiting factors in more than 30 % of paddy fields in Egypt, where the developed varieties cannot perform well under water shortage. Therefore, the development of water stress tol- erant genotypes that maintain good yield under drought condition is a priority area of rice research for sustain- able rice production (Abdallah et al., 2013). Drought af- fects rice at morphological, physiological, and molecu- lar levels where it reduces plant height, tiller numbers plant-1, panicle length, leaf area, increase sterility, induce leaf rolling, reduce water potential, stomatal closure, dry matter accumulation and decrease photosynthetic capac- ity. Moreover, high temperature is often accompanied with low water supply, so the primary aim of rice breed- ing program is developing promising varieties tolerant to both types of stresses (Abdel-Hafez et al., 2017). To increase the yield potential and to reduce the yield gap, improving varietal adaptability, yield potential and grain quality under stress are needed. Conventional plant breeding played important role in developing rice variet- ies tolerant to abiotic stresses, which is very complex due to the intricate interactions between stress factors that af- fect plant growth and development. Rice breeders follow all breeding methods to improve characters of the newly developed varieties to cover the continuous changes in breeding objectives. The information about the used va- rieties is essential to plan a successful breeding program. The diallel analysis provides information on the nature and amount of genetic parameters and general and spe- cific combining abilities of parents and their crosses. Combining ability analysis is a useful method to assess the potential ability of varieties. This will be helpful in choosing parents in hybridization programs to get desir- able segregates (Gaballah et al., 2021a). The information about gene effects including additive and dominance gene effects, non-allelic gene interaction i.e. additive × additive, additive × dominance, and dominance × domi- nance are very important and essential to rice breeders for improving new rice varieties under both natural as well as adverse conditions (Hassan et al., 2023). Today yield safety has gained more significance because of the forecasted climate changes. It can only be improved if future breeding attempts are based on the valuable new knowledge acquired on yield (Barnabas et al., 2008). The major objectives of the study to identify some rice genotypes tolerant to drought stress conditions as donors for rice breeding program, to study the variation among the studied genotypes and their characters in terms of drought tolerance in all traits and determine the general and specific combining abilities, genetically analysis in parents and the possible crosses of rice to identify the most important traits and genotypes for drought toler- ance in rice. 2 MATERIALS AND METHODS The present study was carried out at the Experi- mental Farm of the Rice Research and Training Center (RRTC), Sakha, Kafr El-Sheikh, Egypt, during rice grow- ing seasons, 2022 and 2023. Eight rice genotypes namely UYR 2184, UYR 3472, GZ10487, GZ10739, WAB 638-1, IRAT 112, Giza 179 and Sakha 108 representing a wide range of diversity for several agronomic characters and drought resistance measurements were selected for this study. The names, pedigree and origin of these genotypes are presented in Table (1). 2.1 EXPERIMENTAL WORK In 2022 season, seeds of the parental genotypes were sown at three planting dates (May 1st, May 10th and May 20th) in order to overcome the differences in time of flowering. Seedling of each parent were individuals transplanted in the permanent field in five rows. Each row was five meters long and contained 25 hills. At flow- ering the eight parents were diallel crossed in all possible Genotype Origin Type drought tol- erance UYR 2184 Ukraine Japonica Sensitive UYR 3472 Ukraine Japonica Sensitive GZ10487 Egypt Japonica Moderate GZ10739 Egypt Japonica Tolerant WAB 638-1 Côte d’Ivoire Indica Tolerant IRAT 112 Côte d’Ivoire Indica Tolerant Giza 179 Egypt Indica/Japonica Moderate Sakha 108 Egypt Japonica Sensitive Table 1: Origin and type of the eight rice genotypes used as parents in the studied half diallel cross. Acta agriculturae Slovenica, 121/2 – 2025 3 Identifying gene actions to rice yield and its components traits under both normal and drought conditions combinations without reciprocal giving a total of twenty- eight crosses according to Griffing’s, Method 2, Model 1 includes both parental lines and their F1 hybrids, assumes genotypes are fixed (not randomly sampled) and ignores maternal/paternal effects (reciprocal differences). The observed phenotypic value of a hybrid (Yij) is modeled Yij = μ + gi + gj + sij + eij Where: μ: grand mean. gi, gj: GCA effects of parents i and j. sij: SCA effect for the cross between i and j and eij: random error term. In 2023 season, all hybrid combination seeds and their parental were sown in May 10th in the nursery and after 30 days the seedlings of the parents and their F1 crosses were individually transplanted in randomized complete blocks design with three replications. The rows were five meters long with 20 cm between rows and comprised 25 hills each of a single plant. The genotypes were grown under both natu- ral and drought conditions. Drought stress was imposed by applying irrigation every 12 days without remaining water. The amount of irriga- tion water applied was measured by flowmeter. Weeds were chemically controlled by applying 2 liters of Saturn/ feddan after transplanting by five days. Nitrogen fertilizer was applied ac- cording to both recommended rate and applica- tion time. The physical and chemical analysis of soil properties of the experimental field in both 2022 and 2023 seasons are shown in Ta- ble 2, according to USDA soil survey manual (2017). 2.2 STUDIED CHARACTERS Growth characters, plant samples were collected randomly from each treatment at tillering, panicle initia- tion, booting and heading stages to estimate the follow- ing characters. Days to 50 % heading (day): It was count- ed as number of days starting from date of sowing till the date of main panicle appearance. Plant height (cm): It was measured from the soil surface to the tip of the tallest panicle of each plant at maturity. Number of tillers plant-1: It was determined by counting the number of til- lers per hill, when the panicles were at the full ripe stage. Panicle length (cm): The main panicle was measured from panicle base to the upper most of the panicle (IRRI, 1996). Flag leaf area (cm2): It was measured at the maxi- mum tillering stage according to the formula reported by Yoshida et al. (1976) as follows: Leaf area (cm2) = K × leaf length (cm) × leaf width (cm) K, is the correction factor which can be used for all growth stages, except the seedling and maturity stag- es. It approximately equals 0.75. Chlorophyll content (SPAD): Total chlorophyll content was determined by using chlorophyll analytical apparatus; chlorophyll me- ter SPAD-502 Minolta Camera Co. Ltd., Japan. Five flag leaves were measured from the widest part of the leaf of the main culm for each entry in all replications. Relative water content (RWC): It was determined by the method of Barrs and Weatherley, (1962). Leaf rolling: It was re- corded based on methods proposed by De Datta et al., (1988); Loresto and Chang (1994) as shown in Table (3). Grain yield and its components: The plants were individually harvested and threshed separately to deter- mine the grain yield and yield components. Number of panicles plant-1: It was determined by counting the num- ber of panicles plant-1 at the ripening stage. 1000-grain Characters 2022 season 2023 season Mechanical analysis: Sand % 16.20 15.95 Clay % 55.05 55.60 Silt % 28.75 28.45 Chemical analysis: 1-pH 7.3- 7.8 7.9- 8.3 2-Organic matter % 1.45 1.67 3-E.C (ml mhose) 1.95 2.04 4- (Ca++) 2.00 1.97 5- (Mg++) 20.00 23.00 6-(Na+) mg 100 g-1 93.54 99.00 7-(K+) mg 100 g-1 42.00 39.40 8-P mg 100 g-1 2.06 1.90 9-Mg mg 100 g-1 85.00 90.00 Fe ppm 8.08 7.13 Mn ppm 3.08 4.55 Zn ppm 0.93 0.85 Cu ppm 1.00 1.83 Table 2: Physical and chemical analysis of the experimental soil (0-30 cm) depth. Acta agriculturae Slovenica, 121/2 – 20254 M. GABALLAH et al. mass (g): It was recorded by the mass of 1000 random chosen filled grains plant-1 at ripening stage. Steril- ity percentage (%): The unfilled grains of the main panicle were separated and counted. Then, sterility percentage was calculated as follows: Sterility (%) = (number of unfilled grains/panicle)/ Number of total spikelets) * 100 Grain yield plant-1 (g): It was recorded as the mass of grain yield of each individual plant and ad- justed to 14 % moisture content. Water use efficiency (g ml-1): It was measured by the following formula WUE = Dry matter production (g)/Water loss (ml) Water use efficiency was expressed in gDM-ml- 1H2O 2.3 STATISTICAL ANALYSIS The data were analyzed by using the ordinary analysis of variance to test the significant differences among the genotypes studied. Data of each experi- ment was analyzed using procedure of Griffing (1956) (method II, model I) to estimate the general and spe- cific combining ability. 2.4 ESTIMATION OF HETEROSIS Heterosis as proposed by Mather and Jinkes (1982) was determined as the deviation of the F1 means from mid-parents (MP) and better parent (Bp) means and expressed as percentage. Average heterosis value for each trait was computed as parents vs. F1 hy- brids as follows: Mid-parents Heterosis (MP): To test the significance of heterosis for the above case, LSD. values were estimated according to the fol- lowing formula suggested by Wynne et al. (1970). Better -parent heterosis (BP): The better parent for any character is that having the higher mean value, except for heading date and plant height, where the better parent which has the lower mean value. Appropriate LSD values were cal- culated to test the significance of the heterotic effects for better parent, according to the following formula, suggested by Wynne et al. (1970). Where: : Mean value of the first generation, MP: Mid-parents value, BP: Value of the better par- ent, t: Tabulated (t) value at certain probability level and given degrees of freedom, (df), MSe: Error mean squares from the analysis of variance, r: Number of replications. 2.5 ESTIMATION OF COMBINING ABILITY The statistical analysis was done using method 2, model 1 of Griffing (1956). This a fixed and most appropriate model as its requirements can be met experimentally. Data were analyzed according to Cochran and Cox (1967) to test the significance of the different genotypes. The analysis of variance was calculated for each character. Then, the differences Scores Reaction Leaf rolling Leaf firing 0 Highly resist- ant No symptoms of stress No symptoms 1 Resistant No rolling Slight leaf tip dry- ing 3 Moderately resistant Partially rolled, unrolled in evening Leaf tip drying extende to 1/4 in top three leave 5 Intermediate Partially; unroll- ing at late even- ing and early morning. Half of younger leaf blades dried, all lower leaf dried. 7 Susceptible Complete, unrolling in morning 3/4 of younger leaf blade dried. 9 Highly suscep- tible Like tube; no unrolling in morning All leaves dried Table 3: Scores and symptoms for leaf rolling and drought resistance at vegetative stage. Acta agriculturae Slovenica, 121/2 – 2025 5 Identifying gene actions to rice yield and its components traits under both normal and drought conditions between genotypes were further partitioned to GCA and SCA, follow Griffing (1956) (Method2, Model1) as a fixed model. Variances due to general and specific combining abilities were estimated. The mathematical model for a single cross value (Xij) as given by Griff- ing (1956). 2.6 PHENOTYPIC CORRELATION COEFFI- CIENT AND HEATMAP Phenotypic correlations between all possible pairs of the studied characters were estimated by the application of the formula used by Dewey and Lu (1959), as follows: Phenotypic correlation (Rph) = {(Cov. XY)/ √ (Var. X * Var.Y)} Where, Cov. XY = Phenotypic covariance be- tween X and Y characters, Var. X and Var. Y = Vari- ance of characters X and Y. The “R” values were tested for significance against the minimum significant “R” values calculated for different degrees of freedom listed by Snedecor (1956). All calculated were done by Genes Package Software Version 2019. A heat- map with clustering was generated using the heatmap package implemented in R software (R Core Team 2021). 3 RESULTS 3.1 ANALYSIS OF VARIANCE The mean square values for days to heading, plant height, number of tillers plant-1, panicle length, flag leaf area, leaf rolling, chlorophyll content and relative water content were given in Table 4, 5 and 6. Genotypes, par- ents, crosses and parent vs. crosses mean squares were found to be highly significant for all the traits studied in both natural and drought condition, except leaf rolling under natural conditions. Both general and specific com- bining ability variance were found to be highly signifi- cant for all characters studied at the two environments except leaf rolling and water use efficiency. The GCA: SCA ratios were found to be higher than unity under all environments for most traits, except leaf rolling under natural condition was less than unity. 3.2 MEAN PERFORMANCE The mean performance for genotypes of all char- acters studied in both environments are given in sup- plementary Table 7, 8 and 9. For days to heading, the parents, UYR 2184 and UYR 3472 and the crosses UYR 2184 × UYR 3472, and UYR 2184 × Giza179 gave the earliness mean values under both natural and drought condition. With respect to plant height, the most desir- able mean values towards dwarfing were obtained from the parents UYR 2184 and UYR 3472 under both natu- Source of vari- ance df Days to heading (day) Plant height (cm) Number of tillers plant-1Panicle length (cm) N D N D N D N D Replication 2 1.03 8.90** 36.21** 4.69* 0.65 0.57 0.12 0.32 Genotypes 35 322.56** 264.35** 367.75** 378.21** 45.54** 37.33** 45.09** 27.09** Parents (P) 7 770.33** 581.99** 656.87** 496.36** 63.27** 68.03** 72.22** 48.98** Crosses (C) 27 214.87** 190.65** 305.54** 359.80** 41.72** 29.67** 38.37** 22.38** P vs. Cross 1 96.01** 30.57** 23.35** 48.21** 24.51** 29.19** 36.56** 0.94 Error 70 1.57 1.67 4.51 2.93 2.21 1.60 1.84 1.49 GCA 7 382.17** 263.99** 371.10** 403.76** 44.57** 34.26** 42.63** 28.56** SCA 28 38.86** 44.15** 60.45** 56.65** 7.83** 6.99** 8.13** 4.15** Error 70 0.52 0.56 1.50 0.98 0.74 0.53 0.61 0.50 GCA:SCA --- 9.83 5.98 6.14 7.13 5.69 4.90 5.24 6.89 Table 4: Mean of squares estimates of the ordinary and combining ability analysis for growth characters under both natural and drought conditions. N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Acta agriculturae Slovenica, 121/2 – 20256 M. GABALLAH et al. ral and drought condition, and the dwarfing values were obtained from the crosses UYR 2184 × UYR 3472 and UYR 2184 × Sakha 108 under natural conditions, in ad- dition to the crosses GZ10487 × Sakha108 and GZ10739 × Sakha108 under drought condition. Concerning the number of tillers plant-1, the parents Giza179 and Sakha 108 got the highest mean values under natural condition and the parents GZ10487 and WAB 638-1 showed the highest mean values under drought condition and the crosses UYR 3472 × IRAT 112 and UYR 3472 × Giza179 gave the highest mean values under natural and drought condition. While, the parents UYR 2184 and UYR 3472 and the crosses UYR 2184 × UYR 3472 and UYR 2184 × Giza 179 showed the lowest mean values under natural and drought condition. For panicle length, the parents IRAT 112 and Sakha 108 illustrated the highest mean Source or variance df Chlorophyll content (SPAD) Flag leaf area (cm2) Leaf rolling Relative water content N D N D N D N D Replication 2 5.42** 1.87 5.08** 1.64 0.53 13.21** 0.74 30.98** Genotypes 35 74.76** 69.08** 90.83** 69.29** 0.83 3.37** 47.97** 77.36** Parents (P) 7 32.67** 38.47** 122.60** 87.94** 0.80 12.67** 53.31** 85.25** Crosses (C) 27 82.05** 78.72** 77.62** 64.24** 0.85 0.94 44.54** 77.77** P vs. cross 1 172.63** 22.93** 225.26** 75.20** 0.29 3.82 103.03** 11.18** Error 70 3.18 2.54 1.82 8.21 0.42 0.39 2.95 3.85 GCA 7 26.11** 35.15** 84.84** 47.55** 0.25 1.25 53.94** 66.48** SCA 28 24.62** 19.99** 16.64** 16.98** 0.28 1.09 6.50** 15.61** Error 70 1.06 0.85 0.61 2.74 0.14 0.13 0.98 1.28 GCA:SCA --- 1.06 1.76 5.10 2.80 0.87 1.14 8.30 4.26 Source or variance df Number of panicles plant-1 1000-grain mass (g) Sterility percentage Grain yield plant-1 (g) Water use effi- ciency (g ml-1) N D N D N D N D N D Replication (Rep) 2 1.16 3.68* 0.79 1.81 0.33 6.02** 5.22** 25.48** 0.00** 0.02** Genotypes (G) 35 48.91** 37.10** 39.06** 24.82** 12.10** 265.39** 112.17** 153.23** 0.04** 0.14** Parents (P) 7 70.13** 68.84** 26.13** 21.38** 12.14** 423.90** 128.93** 123.08** 0.05** 0.11** Crosses (C) 27 44.05** 28.58** 40.87** 23.86** 8.63** 210.91** 104.43** 165.96** 0.04** 0.15** P vs. F1 1 31.49** 44.92** 80.79** 74.67** 105.24** 626.92** 203.87** 20.58** 0.07** 0.02** Error 70 1.47 1.00 1.37 1.69 1.61 2.43 1.00 0.52 0.00 0.00 GCA 7 49.19** 34.61** 19.07** 9.06** 6.46** 94.55** 153.34** 210.43** 0.06 0.19 SCA 28 8.08** 6.80** 11.51** 8.08** 3.42** 86.94** 8.40** 11.24** 0.00 0.01 Error 70 0.49 0.33 0.46 0.56 0.54 0.81 0.33 0.17 0.00 0.00 GCA: SCA --- 6.09  5.09 1.66  1.12  1.89  1.09  18.25  18.73  18.25 18.73  Table 5: Mean square estimates of the ordinary and combining ability analysis for growth characters under both natural and drought conditions. Table 6: Mean squares estimate of the ordinary and combining ability analysis for grain yield and its components characters under both natural and drought conditions. N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Acta agriculturae Slovenica, 121/2 – 2025 7 Identifying gene actions to rice yield and its components traits under both normal and drought conditions values under natural condition therefor the parents WAB 638-1 and Sakha 108 gave the highest mean values under drought condition, However the crosses GZ10739 × WAB 638-1 and WAB 638-1 × IRAT 112 gave the highest mean values under natural condition in addition to the cross- es GZ10739 × WAB 638-1 and WAB 638-1 × Sakha108 gave the highest mean values under drought condition. While, the parents UYR 2184 and UYR 3472 and the crosses UYR 2184 × UYR 3472 and UYR 2184 × IRAT 112 obtained the lowest mean values under natural and drought condition. With respect to chlorophyll content, the parents WAB 638-1 and Giza 179 showed the high- est mean values under either natural and drought condi- tion, and the crosses UYR 3472 × GZ10739 and WAB 638-1 × Sakha108 gave the highest mean values under natural condition, and the crosses UYR 2184 × GZ10739 and WAB 638-1 × Sakha108 displayed the highest mean values under drought condition. Concerning the flag leaf area, the parents WAB 638-1 and GZ10739 showed the highest mean values of the flag leaf area under either natural and drought condition, and the crosses GZ10739 × WAB 638-1 and GZ10739 × IRAT112 gave the highest mean values of the flag leaf area under natural condition, and the crosses GZ10739 × IRAT112 and WAB 638-1 × IRAT 112 provided the highest mean values of the flag leaf area under drought condition. While, the parents UYR 3472 and GZ10487 and the crosses UYR 2184 × Giza 179 and UYR 2184 × Sakha 108 got the lowest mean values under both natural and drought conditions. For leaf rolling, the parents UYR 2184 and GZ10487 gave the highest mean values under natural condition, and the parents UYR 2184 and Sakha 108 gave the highest mean values under drought condition, and the crosses UYR 2184 × UYR 3472 and IRAT 112 × Sakha108 provided the highest mean values under natural condition, and the crosses UYR 2184 × UYR 3472 and Giza179 × Sakha108 obtained the highest mean values under drought condi- tion. While, the parents UYR 3472 and Giza 179 and the crosses GZ10487 × GZ10739, GZ10739 × WAB 638-1 and WAB 638-1 × IRAT 112 got the lowest mean values of the leaf rolling under both natural and drought condi- tions. concern relative water content, the parents Sakha 108 and IRAT 112 showed the highest mean values under both natural and drought conditions, the crosses UYR 3472 × Giza179 and UYR 3472 × IRAT 112 got the high- est mean values under both natural and drought condi- tions, respectively. On the other hand, the parent UYR 3472 gave the lowest mean values under natural condi- tion, and the parent GZ10487 illustrated the lowest mean values under drought condition, and the cross UYR 2184 × GZ10739 gave the lowest mean values under both nat- ural and drought conditions. Concerning the number of panicles plant-1, the parents GZ10487 and WAB 638-1 gave the highest mean values under natural and drought condition, and the crosses UYR 3472 × Giza179 and IRAT 112 × Giza179 obtained the highest mean values under natural condition. and the crosses UYR 3472 × GZ10487 and UYR 3472 × Giza179 got the highest mean values under drought condition. While, the parents Sakha 108 and UYR 2184 gave the lowest mean values under natu- ral and drought condition, respectively. and the crosses UYR 2184 × UYR 3472 and UYR 2184 × GZ10739 pro- vided the lowest mean values under natural and drought condition, respectively. For 1000-grain mass, the parents UYR 2184 and IRAT 112 and the crosses UYR 3472 × IRAT 112 and UYR 3472 × Giza179 showed the highest mean values of the 1000-grain weight under natural con- ditions. And the parents GZ10739 and IRAT 112 and the crosses UYR 3472 × Giza179 and WAB 638-1 × IRAT112 provided the highest mean values under drought con- dition. on the other hand, the parent GZ10487 and the cross UYR2184 × GZ10487 gave the lowest mean values under natural and drought condition, respectively. Con- cerning the sterility percentage, the parents GZ10739 and Sakha 108 and the crosses IRAT 112 × Giza179 and Giza179 × Sakha108 displayed the lowest mean values of the sterility percentage under natural conditions, and the parents IRAT112 and Giza179 and the crosses GZ10739 × WAB638-1 and WAB 638-1 × IRAT 112 gave the low- est mean values of the sterility percentage under drought conditions. While, the parent IRAT 112 and the cross UYR 2184 × Giza 179 showed the highest mean values under natural condition, and the parent UYR 3472 and the cross GZ10487 × Sakha108 provided the highest mean values under drought condition. Concerning the grain yield plant-1, the parents GZ10739 and Sakha 108 and the crosses GZ10487 × Sakha108 and IRAT 112 × Giza179, showed the highest mean values of the grain yield plant-1 under natural conditions, and the parents Giza179 and Sakha 108 and the crosses UYR 3472 × GZ10739 and GZ10487 × Giza179 got the highest mean values of the grain yield plant-1 under drought condi- tions. While, the parents WAB 638-1 and IRAT112 and the crosses UYR 2184 × WAB 638-1 and UYR 2184 × IRAT 112 gave the lowest mean values under either nat- ural and drought condition, respectively. For water use efficiency, the parents GZ10739 and Sakha 108 and the crosses GZ10487 × Sakha108 and IRAT 112 × Sakha108 got the highest mean values under natural condition, and the parents Giza179 and Sakha 108 and the crosses UYR 3472 × GZ10739 and GZ10487 × GZ10739 showed the highest mean values of the water use efficiency under drought conditions. While, the parents WAB 638-1 and IRAT112 and the crosses UYR 2184 × WAB 638-1 and UYR 2184 × IRAT 112 provided the lowest mean values under either natural and drought condition, respectively. Acta agriculturae Slovenica, 121/2 – 20258 M. GABALLAH et al. 3.3 HETEROSIS: Useful heterosis, expressed as the percentage devia- tion of F1 mean performance from mid and better par- ents for all studied traits in each natural and drought conditions. Concerning days to heading, data in Table 7, 8, 9 and 10 showed that, eight and fifteen hybrids re- vealed desirable significant and highly significant nega- tive heterotic effects as a deviation from the mid parent, 17 and 21 combinations were obtained significant and highly significant negative heterotic over better parent under both natural and drought condition, respectively. on the other hand, undesirable highly and highly signifi- cant positive heterotic effects were recorded for 11 and 10 hybrids over mid parent and 6 and 6 combinations were obtained significant and highly significant positive heterotic over better parent at the natural and drought environments, respectively. With respect to plant height, 10 and 12 hybrids revealed desirable highly and highly significant negative heterotic effects as a deviation over mid parent, 18 and 23 combinations were showed sig- nificant and highly significant negative heterotic over better parent under both natural and drought condition, respectively. on the other hand, undesirable highly and highly significant positive heterotic effects were recorded for 10 and 9 hybrids over mid parent and 2 hybrids under natural condition and there are no crosses under drought condition significant and highly significant positive het- erotic over better parent at the natural and drought en- vironments, respectively. For number of tillers plant-1, seven and five hybrids showed significant and highly sig- nificant positive heterosis over mid-parent, two and one crosses obtained significant and highly significant posi- tive heterotic over better-parent under both natural and drought condition, respectively. Otherwise, the negative heterotic over mid-parent was found with eleven crosses over mid-parent, and 17 and 26 crosses over better par- ent under natural and drought condition, respectively. Regarding panicle length, five hybrids showed significant and highly significant positive heterosis over mid-parent, one cross obtained significant and highly significant pos- itive heterotic over better-parent under both natural and drought condition, respectively. Otherwise, the negative heterotic over mid-parent was found with eleven and seven crosses over mid-parent, and 19 and 23 crosses over better parent under natural and drought condition, respectively. For to chlorophyll content showed that, 18 and 13 hybrids showed significant and highly significant positive heterosis over mid-parent, 8 and 1 crosses ob- tained significant and highly significant positive heterotic over better-parent under both natural and drought con- dition, respectively. However, the negative heterotic over mid-parent was found with 3 and 10 crosses over mid- parent, and 7 and 22 crosses over better parent under natural and drought condition, respectively. With respect to flag leaf area, three and two hybrids revealed desirable highly and highly significant positive heterotic effects as a deviation from the mid parent, one hybrid obtained significant positive heterotic over better parent under natural condition, but there is no hybrid under drought condition, respectively. on the other hand, undesirable highly and highly significant negative heterotic effects were recorded for 18 and 10 hybrids over mid parent and 21 and 24 over better parent at the natural and drought environments, respectively. These findings indicated that these crosses would be very important in drought breeding program for selecting high flag leaf area plants. With regard to leaf rolling, one and six hybrids showed significant and highly significant positive heterosis over mid-parent, there are no crosses under natural condition, but there are six hybrids obtained significant and highly significant positive heterotic over better-parent under drought condition, respectively. There for, the negative heterotic over mid-parent was found with two and twelve crosses over mid-parent, and 1 and 8 crosses over better parent under natural and drought condition, respective- ly. Regarding relative water content, two and six hybrids revealed desirable significant and highly significant posi- tive heterotic effects as a deviation from the mid parent, one GZ10487 × Giza179 was significant positive heter- otic over better parent under natural condition but, there is no hybrid under drought condition, respectively. on the other hand, undesirable highly and highly significant negative heterotic effects were recorded for 18 and 11 hy- brids over mid parent and 23 and 26 over better parent at the natural and drought environments, respectively. Concerning the number of panicles plant-1, six and five hybrids revealed desirable highly and highly significant positive heterotic effects as a deviation over mid parent, two hybrids obtained significant positive heterotic over better-parent under natural condition and there is no hybrid under drought condition, respectively. There for, undesirable highly and highly significant negative heter- otic effects were recorded for 13 and 15 hybrids over mid parent and 17 and 26 from over better parent at the natu- ral and drought environments. Regarding 1000-grain weight three and four hybrids revealed desirable highly and highly significant positive heterotic effects as a devia- tion over mid parent, three hybrids obtained significant positive heterotic over better-parent under natural con- dition and there is no hybrid under drought condition, respectively. On the other hand, undesirable highly and highly significant negative heterotic effects were record- ed for 16 and 17 hybrids over mid parent and 20 and 28 from over better parent at the natural and drought en- vironments. With respect to sterility percentage, there Acta agriculturae Slovenica, 121/2 – 2025 9 Identifying gene actions to rice yield and its components traits under both normal and drought conditions Crosses Days to heading (day) Plant height (cm) Number of tillers plant-1 MP BP MP BP MP BP N D N D N D N D N D N D UYR 2184 × UYR 3472 -2.62 -12.1** -0.53 -9.14** 5.11** 0.20 4.66 * -7.45** 4.64 25.38** 3.268 -18.7** UYR 2184 × GZ10487 11.25** 0.43 36.92** 18.46** -2.45 -1.71 -8.65** -8.15** 9.97 -1.51 -11.141 -29.3** UYR 2184 × GZ10739 8.90 ** -0.87** 34.87** 17.44** 3.03 3.04* -3.52* -3.55 -14.2** -16.3** -29.7** -38.7** UYR 2184 × WAB 638-1 12.35** 12.67** 40.00** 27.69** -12.8** -9.15** -25.39* -20.1** 31.73** 51.52** 26.45** 8.2** UYR 2184 × IRAT 112 9.64** 6.96** 40.00** 26.15** 11.65** 13.66** -4.06** -3.161* -0.64** -0.28 -14.01* -21.5** UYR 2184 × Giza 179 9.32** 5.73** 35.38** 23.08** 3.49* 5.88** 0.000 -4.15* -24.59 -18.7** -39.5** -40.8** UYR 2184 × Sakha 108 14.97** 11.45** 47.69** 32.31** 2.45 2.86 0.000 -7.45** -35.31 -18.11 -47.9** -35.0** UYR 3472 × GZ10487 19.49** 12.50** -1.05 -7.69** 3.09* 2.22 -3.84* -2.12 12.42* 16.75** -10.06* -13.4** UYR 3472 × GZ10739 12.42** 12.00** -7.29** -8.36** 3.44* -0.19** -3.52* -4.27** -15.6** -27.3** -31.5** -44.9** UYR 3472 × WAB 638-1 15.48** 16.28** -5.15** -1.96 17.48** 17.38** 0.26 5.57** 7.82 -3.93 2.204 -26.1** UYR 3472 × IRAT 112 15.10** 11.16** -6.93** -8.79** 11.86** 10.89** -4.22** -3.44** -5.12 -4.38 -18.7** -19.4** UYR 3472 × Giza179 -15.3** -21.2** -30.2** -34.8** 6.05** 4.74** 2.055 -1.85 -20.5** -29.1** -36.9** -46.6** UYR 3472 × Sakha 108 10.75** 11.31** -10.7** -9.06** 1.44 -0.99 -1.399 -7.77** 20.00** 28.63** -4.382 6.250 GZ10487 × GZ10739 -0.52 -3.65** -1.04 -7.37** -5.77** -4.44** -5.76** -13.7** -1.92 -35.3** -3.75 -45.5** GZ10487 × WAB 638-1 -5.21** -7.20** -6.19** -14.0** 3.75** 6.12** -5.75** -0.61 10.13* -11.55 -8.054 -39.3** GZ10487 × IRAT112 -5.10** -7.69** -7.92** -11.5** -12.3** -14.2** -20.0** -22.4** 13.62** 15.81** 4.69 -15.4** GZ10487 × Giza179 -3.32** -6.67** -3.82** -11.5** 2.32 -7.17** -0.962 -21.1** 12.88** 4.18 11.69* -11.4** GZ10487 × Sakha108 -1.52 -4.92** -4.90** -8.42** -2.3** -2.47 -6.41** -17.6** -3.87 -4.26 -4.382 -27.5** GZ10739 × WAB 638-1 -4.32** -8.30** -4.81** -15.6** -10.6** -8.94** -18.8** -14.8 14.47** -12.74* -2.9 -40.3** GZ10739 × IRAT112 -6.94** -9.12** -9.24** -13.5** -9.12** -11.2** -17.1** -19.8** -7.81 -8.12 -13.5** -32.9** GZ10739 × Giza179 0.00 -3.69 0.00 -9.38** 6.95** -1.32 3.5* -16.34** -11.64** -19.74** -14.19** -31.38** GZ10739 × Sakha108 1.68 -1.63 -1.31 -5.90** -2.68 -12.55** -6.73** -26.28** -14.29** 1.38 -16.33** -23.15** WAB 638-1 × IRAT 112 -1.01 1.14** -2.97** -8.25** -0.66 5.51** -1.047 -7.33** -9.49 -4.18 -18.7** -21.8** WAB 638-1 × Giza179 -5.70 -6.13** -6.19** -15.81** -9.20** -4.38** -19.89** -28.53** -19.05** -21.45** -32.98** -36.99** Table 7: Percentage of heterosis over mid and better parents for growth characters under natural and drought conditions Acta agriculturae Slovenica, 121/2 – 202510 M. GABALLAH et al. WAB 638-1 × Sakha108 -1.51** -9.60** -3.92** -17.53** -12.57** -18.31** -23.56** -39.26** -14.06** -6.09 -28.55** -19.63** IRAT 112 × Giza179 -0.51 -7.78** -2.97** -17.82** -9.09** -9.40** -19.52** -28.76** -28.01** -33.71** -34.29** -44.10** IRAT 112 × Sakha108 -2.46** -12.20** -2.94** -20.46** -14.29** -15.01** -24.80** -33.50** -26.14** -28.26** -32.27** -47.45** Giza179 × Sakha108 -2.62 -9.39** -2.94** -14.58** -0.35 3.45* -1.370 -12.67** -19.95** -17.20** -20.36** -40.21** MP: Mid-Parent, BP: Better Parent, N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Table 8: Percentage of heterosis over mid and better parents for growth characters under natural and drought conditions Crosses Panicle length (cm) Chlorophyll content (SPAD) Flag leaf area (cm2) MP BP MP BP MP BP N D N D N D N D N D N D UYR 2184 × UYR 3472 -3.28 -17.20* -8.88 -39.57** -2.63 -5.15 -2.70 -16.38** -4.83 16.94 -6.05 -18.56* UYR 2184 × GZ10487 -8.66 1.37 -22.40** -20.13** 8.11** 13.18** 2.13 -7.44** -10.00** -6.96 -17.04** -21.84** UYR 2184 × GZ10739 -9.72 12.90* -18.60** -12.162* 7.07* 7.29* 3.62 -8.72** -7.78** 25.28** -19.30** 8.91 UYR 2184 × WAB 638-1 -7.89 8.35 -25.88** -17.42** 13.67** 27.72** 6.17* 0.50 -4.42 5.88 -19.98** -8.51 UYR 2184 × IRAT 112 13.83** 17.83** -9.195* -8.73 9.37** 12.00** -1.06 -11.98** -11.14** -15.51* -24.51** -29.71** UYR 2184 × Giza 179 -11.66* -5.15 -23.14** -27.13** 12.56** 9.89** 3.62 -7.37** 1.98 3.56 -1.25 -19.38** UYR 2184 × Sakha 108 -1.01 1.46 -16.99** -20.49** -4.73 -8.75** -10.78** -21.27** -5.68* -18.50* -9.74** -35.17** UYR 3472 × GZ10487 17.60** 26.21** -4.86 6.16 7.59** 14.88** 1.71 -5.68* 8.55** 8.11 -1.13 -14.42 UYR 3472 × GZ10739 6.98 25.29** -8.53 18.478** 6.78* 13.01** 3.41 -3.48 4.80 -11.59 -9.30** -29.01** UYR 3472 × WAB 638-1 -11.31* -14.95** -31.76** -31.06** 8.28** 1.12 1.21 -20.09** -17.78** 13.22 -31.88** -7.57 UYR 3472 × IRAT 112 -30.72** -18.27** -47.12** -32.54** 19.89** 9.45** 8.523** -13.63** -12.07** -24.19** -26.09** -41.45** UYR 3472 × Giza179 -6.39 -13.74** -22.57** -29.45** -5.55 -7.43* -12.99** -21.66** -20.44** -11.56 -23.91** -35.57** UYR 3472 × Sakha 108 28.37** 17.65** 2.61 -1.64 12.39** -7.09* 5.33 -19.53** -31.68** -15.60 -35.42** -37.05** GZ10487 × GZ10739 -16.31** -1.04 -21.72** -29.15** 23.82** 13.53** 20.77** 0.72 -13.68** -3.89 -18.46** -20.93** GZ10487 × WAB 638-1 -8.74* -20.70** -14.58** -32.51** -2.99 -3.77 -4.15 -21.53** -19.98** -26.93** -28.00** -42.12** GZ10487 × IRAT112 0.56 -2.52 -6.90 -19.02** 2.21 -2.64 -2.39 -20.73** 10.54** -36.71** 1.08 -44.81** GZ10487 × Giza179 16.59** 2.73 13.36** -13.63** 14.75** 3.68 11.64** -8.93** 12.52** 14.18 6.92* -17.82** GZ10487 × Sakha108 -5.71 4.05 -7.19 -14.98** -10.66** -6.95* -11.48** -16.18** -4.18 -20.09* -7.87** -41.34** Acta agriculturae Slovenica, 121/2 – 2025 11 Identifying gene actions to rice yield and its components traits under both normal and drought conditions Crosses Leaf rolling Relative water content Number of panicles plant-1 MP BP MP BP MP BP N D N D N D N D N D N D UYR 2184 × UYR 3472 -37.50* -55.56** -37.5 -55.5** -3.59* 4.66* -5.147** -14.61** 9.09 19.93** 8.585 -20.41** UYR 2184 × GZ10487 23.08 -38.46** 0 0 -3.77* -10.25** -4.460* -23.45** 7.31 -3.79 -14.7** -31.32** UYR 2184 × GZ10739 -23.08 -33.33** -37.5 0 -3.26* 0.91 -6.199** -12.12** -17.60** -21.69** -34.03** -43.49** UYR 2184 × WAB 638-1 -23.08 -25.00* -37.5 12.5 -6.23** -10.60** -10.49** -19.30** 30.54** 42.15** 21.643** 6.03 UYR 2184 × IRAT 112 -16.67 -21.74 -37.5 12.5 -4.87** -0.32 -9.668** -10.21** -0.68 -5.68 -14.78** -23.67** UYR 2184 × Giza 179 -33.33 -38.46** -37.5 0 -7.11** -2.61 -10.93** -14.94** -28.02** -25.00** -43.62** -46.20** UYR 2184 × Sakha 108 -33.33 -35.14** -37.5 -36.8** -1.54 12.33** -5.015** -6.80** -38.85** -17.15** -51.92** -34.34** UYR 3472 × GZ10487 23.08 -38.46** 0 0 -1.86 -5.53** -4.133* -17.93** 8.71 9.66* -13.93** -18.76** UYR 3472 × GZ10739 23.08 -16.67 0 25 -7.07** -8.58** -11.30** -18.87** -19.41** -30.99** -35.70** -48.27** UYR 3472 × WAB 638-1 -7.69 -16.67 -25 25 -3.55* -4.01* -9.358** -12.53** 5.83 -5.47 -1.80 -25.05** UYR 3472 × IRAT 112 0 4.35 -25 50.000* -0.72 -6.05** -7.167** -14.24** -6.71 -7.86 -20.26** -21.83** UYR 3472 × Giza179 -20.00** -30.77** -25 12.5 -4.04** 1.23 -9.410** -9.91** -20.54** -30.59** -37.97** -48.30** UYR 3472 × Sakha 108 -46.67 -62.16** -50.00** -63.15** -2.99* 4.57* -7.870** -11.66** 20.34** 31.59** -5.71 9.13 GZ10487 × GZ10739 0 42.86* 0 66.667* -3.09* -4.80* -5.380** -15.95** -3.52 -40.78** -4.508 -50.00** GZ10739 × WAB 638-1 -23.75** -8.93 -32.94** -22.72** 8.61** 10.29** 4.70 -10.61** -13.84** -4.05 -18.18** -28.07** GZ10739 × IRAT112 -17.49** 1.47 -28.16** -14.26** -0.57 -8.76** -7.27* -26.15** -13.91** -19.21** -16.84** -33.69** GZ10739 × Giza179 -6.32 -2.26 -10.00* -16.27** 12.81** -8.89** 7.12* -20.69** -20.55** -19.19** -28.46** -44.61** GZ10739 × Sakha108 2.13 6.54 -5.88 -11.62* -4.63 -7.31* -7.80* -17.36** -16.35** -20.66** -23.84** -44.61** WAB 638-1 × Giza179 -21.81** -17.24** -28.70** -36.47** 15.44** -14.37** 13.64** -25.98** -20.39** -7.66 -31.53** -45.36** WAB 638-1 × Sakha108 -13.93** -23.62** -18.23** -42.94** 17.23** 7.92* 16.897** -4.25 -9.03** 9.75 -20.95** -33.81** IRAT 112 × Giza179 -19.75** -5.10 -27.58** -30.46** -8.64** -12.64** -10.37** -19.10** -16.26** -16.67* -26.88** -43.36** IRAT 112 × Sakha108 -2.14 8.06 -8.04* -22.98** 45.62** 37.57** 40.29** 25.06** -13.57** -11.35 -23.72** -38.71** Giza179 × Sakha108 13.31** 5.18 8.50 -5.71 -11.71** -21.80** -13.32** -23.63** 3.04 1.33 1.78 -23.24** MP: Mid-Parent, BP: Better Parent, N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Table 9: Percentage of heterosis over mid and better parents for growth characters under natural and drought conditions Acta agriculturae Slovenica, 121/2 – 202512 M. GABALLAH et al. Crosses 1000-grain mass (g) Sterility percentage Grain yield plant-1 (g) Water use efficiency (g ml) MP BP MP BP MP BP MP BP N D N D N D N D N D N D N D N D UYR 2184 × UYR3472 -4.9 -5.5 -7.2* -25.2** 6.3 21.9** 7.7 275.0** -0.1 -12.2** -0.3 -46.8** -0.1 -12.2** -0.3 -16.4** UYR 2184 × GZ10487 -28.1** -13.1** -32.7** -31.5** 20.3* 24.6** 47.6 237.5** -13.6** -28.2** -25.5** -44.0** -13.6** -28.2** -25.5** -44.0** UYR 2184 × GZ10739 -4.5 11.86** -5.4 -7.447* -15.6 -9.01** -3.54** 147.5** -12.2** -26.9** -24.8** -44.1** -12.2** -26.9** -24.8** -44.1** UYR 2184 × WAB 638-1 -7.20** -13.0** -13.2** -23.4** 19.41* -23.2** 46.6 90.36** -8.0 -26.8** -13.0** -47.1** -7.98** -26.8** -13.0** -38.2** UYR 2184 × IRAT 112 -0.1 -6.84* -6.042* -17.1** 21.3** -43.8** 26.63* 50.0 -10.8** -33.2** -15.3** -49.7** -10.8** -33.2** -15.3** -45.1** UYR 2184 × Giza 179 -3.8 5.8 -10.5** -18.4** 7.3 -34.4** 32.2 80.00* -15.7** -7.02* -28.7** -29.1** -15.7** -7.0** -28.7** -24.1** UYR 2184 × Sakha 108 -3.1 -13.5** -3.4 -25.4** 3.3 -31.8** 35.92* 102.5 -11.1** -5.68** -23.4** -34.5** -11.1** -5.6** -23.4** -17.9** UYR 3472 × GZ10487 -30.7** -21.1** -36.6** -34.3** 28.4** 43.4** 9.5 78.2** -13.4** -19.2** -25.5** -35.8** -13.4** -19.2** -25.5** -35.8** UYR 3472 × GZ10739 -15.1** 0.6 -18.0** -11.9** -5.0 26.2** -14.6 55.3** -21.2** -32.0** -32.7** -47.0** -21.2** -32.0** -32.7** -47.0** GZ10487 × WAB 638-1 60 71.43** 60 100.0** -1.14 -4.07* -4.981** -12.31** 9.67* -14.06** -7.787 -41.12** GZ10487 × IRAT112 -11.11 84.62** -20 140.0** 5.41** 7.65** 0.784 -1.8 13.94** 12.78** 3.825 -18.03** GZ10487 × Giza179 -33.33 50.00** -42.85 50.00* 7.71** 12.78** 4.000* -0.16 12.53** 0.96 10.381** -13.93** GZ10487 × Sakha108 -33.33 -33.33** -42.85 -52.63** -4.37** -6.66** -7.099** -21.39** -3.03 -0.83 -4.382 -26.23** GZ10739 × WAB 638-1 0 33.33 0 33.33 -4.74** -9.42** -6.264** -19.57** 14.47** -12.74** -2.929 -40.30** GZ10739 × IRAT112 -11.11 45.45 -20 60 -5.03** -9.24** -7.055** -19.57** -9.48* -11.90** -16.73** -35.98** GZ10739 × Giza1790 71.43* -14.286 50.000* -4.82** -3.99* -5.905** -17.38** -11.64** -19.74** -14.19** -31.38** GZ10739 × Sakha108 -33.33 -4 -42.857 -36.84** -2.04 2.17 -2.546 -16.29** -14.29** 3.28 -16.33** -23.15** WAB 638-1 × IRAT112 11.11 45.45 0 60 -3.85** -2.19 -4.367** -13.28** -12.26* -11.00* -19.76** -27.85** WAB 638-1 × Giza179 0 28.57 -14.286 12.5 -0.7 2.87 -1.17 -11.35** -19.05** -21.45** -32.98** -36.99** WAB 638-1 × Sakha108 -16.67 -28.00** -28.571 -52.63** -5.00** 3.31 -6.038** -15.09** -14.06** -3.84 -28.55** -19.63** IRAT 112 × Giza179 45.45 84.62** 14.286 50.00* -3.17* 0.66 -4.143** -14.37** -26.63** -33.40** -34.29** -43.29** IRAT 112 × Sakha108 27.27 -16.67 0 -47.36** -1.65 0.21 -3.247* -18.70** -24.72** -26.26** -32.27 -45.18** Giza179 × Sakha108 42.86* -33.33** 42.857 -52.63** -0.94 6.24** -1.562 -14.70** -19.95** -15.66** -20.36** -40.21** MP: Mid-Parent, BP: Better Parent, N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Table 10: Percentage of heterosis over mid and better parents for growth characters under natural and drought conditions Acta agriculturae Slovenica, 121/2 – 2025 13 Identifying gene actions to rice yield and its components traits under both normal and drought conditions is no hybrid desirable significant and highly signifi- cant negative heterotic effects as a deviation from the mid parent under natural condition, but there are six hybrids under drought condition, one and one com- binations were obtained significant and highly signifi- cant negative heterotic over better parent under both natural and drought condition, respectively. However, undesirable highly and highly significant positive het- erotic effects were recorded for 18 and 19 hybrids over mid parent and 13 and 21 combinations were obtained significant and highly significant positive heterotic over better parent at the natural and drought environ- ments, respectively. Concerning the grain yield plant-1, two and twelve hybrids revealed desirable highly and highly significant positive heterotic effects as a devia- tion over mid parent, one hybrid obtained significant positive heterotic over better-parent under natural condition and there is no hybrid under drought con- dition, respectively. Otherwise, undesirable highly and highly significant negative heterotic effects were recorded for 19 and 13 hybrids over mid parent and 21 and 28 from over better parent at the natural and drought environments. For water use efficiency, two and twelve hybrids showed significant and highly UYR 3472 × WAB 638-1 -14.0** -18.6** -21.4** -26.1** 27.5** 106.0** 8.7 238.3** -16.9** -24.2** -21.6** -43.7** -16.9** -24.2** -21.6** -34.5** UYR 3472 × IRAT 112 -17.4** -25.4** -24.1** -32.8** 13.7 -5.8 10.5 20.62** -13.3** -27.0** -18.0** -43.6** -13.3** -27.0** -18.0** -38.7** UYR 3472 × Giza179 -10.5** -13.2** -14.8** -29.2** 38.4** 38.5** 17.6* 67.4** -15.5** -4.82* -28.6** -25.5** -15.5** -4.82** -28.6** -20.7** UYR 3472 × Sakha 108 -7.9* -20.9** -9.8** -27.8** 7.7 -26.5** -12.3 -22.7** -15.8** -0.7 -27.6** -29.1** -15.8** -0.7 -27.6** -11.6** GZ10487 × GZ10739 0.7 12.4** -4.9 -18.7** 5.1 10.3** -1.0 9.4 -2.9 2.8* -3.7* -19.2** -2.9* 2.8* -3.7* 0.2 GZ10487 × WAB 638-1 -18.4** -9.7** -18.4** -30.5** 21.8* 51.2** 21.8 91.8** -8.6** 1.7 -17.1** -29.5** -8.6** 1.7 -17.1** 10.6** IRAT 112 × Giza179 -3.5** -18.5** -15.2** -37.1** 40.4** 91.9** 22.2** 83.1** -7.4** 11.7** -18.0** -7.1** -7.4** 11.7** -18.0** 10.6** IRAT 112 × Sakha108 1.9 -10.7** -4.5 -23.9** 56.6** 16.8** 30.4** -0.3 -10.4** 14.3** -19.2** -12.0** -10.4** 14.3** -19.2** 22.8** Giza179 × Sakha108 16.0** 1.7 8.3* -8.1* 64.4** 7.2 56.04** -4.7 6.1** 13.2** 4.04* -32.0** 6.1** 13.2** 4.0** 6.7** GZ10487 × IRAT112 12.8** 4.0 12.2** -19.2** 12.0 33.5** -2.2 36.9** -9.8** -3.5* -18.6** -31.1** -9.8** -3.5** -18.6** 3.9** GZ10487 × Giza179 30.6** 30.8** 14.3** -11.8** 40.8** 85.5** 40.3** 81.2** 0.2 6.8** -2.0 -22.9** 0.2 6.8** -2.0 13.8** GZ10487 × Sakha108 -13.4** -15.3** -19.2** -36.2** 40.0** 27.7** 32.3** 11.27* -1.6 17.8** -1.7 -20.9** -1.6 17.8** -1.7 24.2** GZ10739 × WAB 638-1 -17.5** -24.6** -22.1** -31.8** 37.2** 50.3** 29.2** 92.6** -4.78** 4.8** -14.3** -26.4** -4.7** 4.8** -14.3** 15.5** GZ10739 × IRAT112 -13.9** -26.9** -18.3** -33.3** 33.1** 51.2** 22.8** 56.3** -11.0** 3.9** -20.2** -24.9** -11.0** 3.9** -20.2** 15.2** GZ10739 × Giza179 -4.2 8.07* -11.7** -13.9** 29.1** 6.6 21.2* 5.0 -1.4 8.8** -2.7 -20.6** -1.4 8.8** -2.6* 19.2** GZ10739 × Sakha108 -0.7 2.6 -2.0 -9.03** 20.50* 105.5** 7.7 80.39** 3.49* 10.85** 2.8 -24.6** 3.4* 10.8** 2.7* 18.4** WAB 638-1 × IRAT 112 -18.2** -20.2** -18.8** -31.7** 8.6 95.67** -5.2 64.64** 0.0 0.7 -0.3 -20.5** 0.0 0.7 -0.3 -2.6 WAB 638-1 × Giza179 -12.8** -6.6 -23.8** -29.7** 48.5** 97.4** 48.0** 60.0** -5.9** 9.19** -16.4** -12.9** -5.99** 9.19** -16.4** 4.5** WAB 638-1 × Sakha108 -6.3* -11.8** -12.7** -26.6** 30.0** 57.5** 22.9* 16.7** -6.3** 14.4** -15.2** -15.6** -6.3** 14.4** -15.2** 18.6** MP: Mid-Parent, BP: Better Parent, N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Acta agriculturae Slovenica, 121/2 – 202514 M. GABALLAH et al. significant positive heterosis over mid-parent, 2 and 13 crosses obtained significant and highly significant positive heterotic over better-parent under both natu- ral and drought condition, respectively. Otherwise, the negative heterotic over mid-parent was found with 21 and 13 crosses over mid-parent, and 22 and 13 crosses over better parent under natural and drought condi- tion, respectively. 3.4 GENERAL COMBINING ABILITY EFFECTS (GCA) Variation in general combining ability effects was estimated among the eight parental genotypes for studied traits to identify the best combiner par- ents for subsequent hybrid development program (Table 11, 12 and 13). For number of days to head- ing six and four parents showed desirable significant and highly significant in negative direction effects under both natural and drought conditions, respec- tively. Regarding plant height, six and four parents showed desirable significant and highly significant in negative direction effects under both natural and drought conditions, respectively. For number of till- ers plant-1, four and three parents showed desirable significant and highly significant positive GCA ef- fects under both natural and drought conditions, re- spectively. Concerning panicle length out of four and four parents showed desirable significant and highly significant positive general combining ability effects under either natural and drought conditions, respec- tively. For chlorophyll content, three parents showed desirable significant and highly significant positive GCA effects under both natural and drought condi- tions, respectively. With respect to flag leaf area, four and three parents showed desirable significant and highly significant positive general combining abil- ity effects under either natural and drought condi- tions, respectively. Otherwise, four and three parents provided negative significant and highly significant in general combining ability under both natural and drought condition, respectively. For leaf rolling there are no parents desirable significant and highly sig- nificant positive general combining ability effects under natural condition, but there are three parents desirable significant and highly significant posi- tive general combining ability effects under drought condition, respectively. Regarding the relative water content, four and three parents showed desirable significant and highly significant positive general combining ability effects under either natural and drought conditions, respectively. However, two and four parents obtained negative significant and highly significant in general combining ability under both natural and drought condition, respectively. Regard- ing number of panicles plant-1, four parents showed desirable significant and highly significant positive general combining ability effects under either natural and drought conditions, respectively. On the other hand, four parents provided negative significant and highly significant in general combining ability under Parents Days to heading (day) Plant height (cm) Number of tillers plant-1 Panicle length (cm) N D N D N D N D UYR 2184 -5.09** -3.17** -5.09** -3.17** -2.71** -2.23** -2.49** -2.82** UYR 3472 -1.43** 0.97** -1.43** 0.97** -2.15** -1.82** -2.99** -2.03** GZ10487 -0.93* -0.43 -0.93* -0.43 3.93** 3.44** 1.61** 1.18** GZ10739 -1.23** -1.97** -1.23** -1.97** 1.17** 1.02** -1.39** -0.81** WAB 638-1 9.43** 7.50** 9.43** 7.50** -1.06** -1.12** 0.67** 0.35 IRAT 112 9.15** 10.63** 9.15** 10.63** -0.56* -0.63** 1.83** 1.46** Giza 179 -3.00** -4.93** -3.00** -4.93** 0.62* 1.04** 0.23 1.13** Sakha 108 -6.90** -8.60** -6.90** -8.60** 0.76** 0.29 2.53** 1.53** L.S.D.05 (gi) 0.72 0.58 0.72 0.58 0.50 0.43 0.46 0.42 L.S.D.01 (gi) 0.96 0.77 0.96 0.77 0.67 0.57 0.61 0.55 L.S.D .05(gi-gj) 1.09 0.88 1.09 0.88 0.76 0.65 0.70 0.63 L.S.D .01(gi-gj) 1.45 1.17 1.45 1.17 1.01 0.86 0.92 0.83 Table 11: Estimates of general combining ability effects of the parental genotypes for the studied growth characters under natural and drought conditions. N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Acta agriculturae Slovenica, 121/2 – 2025 15 Identifying gene actions to rice yield and its components traits under both normal and drought conditions Parents Chlorophyll content (SPAD) Flag leaf area (cm2) Leaf rolling Relative water content N D N D N D N D UYR 2184 2.07** 3.24** -2.31** -0.31 0.05 0.28** -3.01** -2.44** UYR 3472 2.18** 1.94** -3.77** -3.49** 0.22 0.35** -3.73** -3.94** GZ10487 -0.58 -0.51 1.53** -0.44 -0.05 -0.08 0.04 -0.67 GZ10739 0.99** 0.54* 1.28** 2.16** -0.18 -0.32** -0.43 -0.96** WAB 638-1 -0.07 -1.44** 3.46** 2.71** -0.08 -0.42** 1.36** 2.24** IRAT 112 -1.21** -1.27** 3.92** 2.18** -0.18 -0.28** 2.79** 3.18** Giza 179 -2.30** -2.47** -2.01** -1.17* 0.22 -0.08 1.99** 2.91** Sakha 108 -1.07** -0.03** -2.11** -1.64** 0.02 0.55** 0.98** -0.33** L.S.D.05 (gi) 0.61 0.54 0.46 0.97 0.22 0.21 0.58 0.67 L.S.D.01 (gi) 0.80 0.72 0.61 1.29 0.29 0.28 0.77 0.89 L.S.D .05(gi-gj) 0.92 0.82 0.69 1.47 0.33 0.32 0.88 1.01 L.S.D .01(gi-gj) 1.21 1.09 0.92 1.95 0.44 0.43 1.17 1.34 Table 12: Estimates of general combining ability effects of the parental genotypes for some growth characters studied under natu- ral and drought conditions. N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. Table 13: Estimates of general combining ability effects of the parental genotypes for grain yield and its component characters under natural and drought conditions. Parents Number of panicles plant-1 1000-grain mass (g) Sterility percentage Grain yield plant-1 (g) Water use efficiency (g ml) N D N D N D N D N D UYR 2184 -3.09** -2.51** -0.52* -0.52* 0.45* 5.85** -4.50** -7.58** -0.09** -0.23** UYR 3472 -2.33** -1.92** -2.57** -2.05** 0.88** 3.25** -5.54** -6.58** -0.11** -0.20** GZ10487 3.83** 3.12** 1.63** 0.05 -0.72** -0.54* 2.79** 3.58** 0.05** 0.11** GZ10739 1.26** 1.12** -0.33 0.97** -0.75** -1.44** 3.20** 4.40** 0.06** 0.13** WAB 638-1 -0.89** -0.99** 0.21 0.27 -0.48* -2.60** -1.56** 0.31* -0.03** 0.01* IRAT 112 -0.73** -0.63** 1.75** 0.50* 1.24** -3.38** -2.23** 0.93** -0.04** 0.03** Giza 179 0.89** 1.26** -0.62** 0.02 0.20 -0.85** 4.31** 3.28** 0.08** 0.10** Sakha 108 1.06** 0.56** 0.46 0.76** -0.82** -0.29** 3.53** 1.65** 0.07** 0.05** L.S.D.05 (gi) 0.41 0.34 0.40 0.44 0.43 0.53 0.34 0.25 0.01 0.01 L.S.D.01 (gi) 0.55 0.45 0.53 0.59 0.57 0.70 0.45 0.33 0.01 0.01 L.S.D .05 (gi-gj) 0.62 0.51 0.60 0.67 0.65 0.80 0.51 0.37 0.01 0.01 L.S.D .01 (gi-gj) 0.83 0.68 0.80 0.89 0.86 1.06 0.68 0.49 0.01 0.01 N: natural condition, D: drought condition, * and ** significant at 0.05 and 0.01 levels of probability, respectively. either natural and drought condition, respectively. Concerning 1000-grain mass, two and three parents showed desirable significant and highly significant positive general combining ability effects under ei- ther natural and drought conditions, respectively. However, three and two parents got negative signifi- cant and highly significant in general combining abili- ty under either natural and drought condition, respec- tively. With respect to sterility percentage, four and six parents showed desirable significant and highly sig- nificant negative general combining ability effects un- der both natural and drought conditions, respectively. Acta agriculturae Slovenica, 121/2 – 202516 M. GABALLAH et al. On the other hand, three and two parents displayed positive significant and highly significant in general combining ability under both natural and drought condition, respectively. Regarding the grain yield plant-1, four and six parents showed desirable signifi- cant and highly significant positive general combining ability effects under either natural and drought con- ditions, respectively. Otherwise, four and two parents Crosses Days to heading (day) Plant height (cm) Number of tillers plant-1 Panicle length (cm) N D N D N D N D UYR 2184 × UYR 3472 -1.99 -5.47** -1.99 -5.47** 0.68 1.78** -0.82 -2.72** UYR 2184 × GZ10487 -2.49* -1.73 -2.49* -1.73 0.87 -0.65 -1.98** -0.37 UYR 2184 × GZ10739 3.14** 3.80** 3.14** 3.80** -1.64* -1.10 -0.65 0.79 UYR 2184 × WAB 638-1 -12.86** -10.00** -12.86** -10.00** 4.82** 5.21** 0.79 2.63** UYR 2184 × IRAT 112 13.62** 13.20** 13.62** 13.20** 1.29 0.15 4.97** 2.52** UYR 2184 × Giza 179 1.91 3.43** 1.91 3.43** -2.56** -1.31 -1.84* -0.65 UYR 2184 × Sakha 108 3.81** 4.10** 3.81** 4.10** -4.96** -2.37** -0.90 -0.55 UYR 3472 × GZ10487 -1.15 -0.20 -1.15 -0.20 0.57 2.38** 2.86** 4.11** UYR 3472 × GZ10739 -0.52 -1.00 -0.52 -1.00 -2.63** -2.77** 2.02** 3.00** UYR 3472 × WAB 638-1 16.15** 13.53** 16.15** 13.53** 0.23 -0.77 -0.37 -1.15 UYR 3472 × IRAT 112 9.76** 8.73** 9.76** 8.73** -0.27 -0.25 -5.53** -3.26** UYR 3472 × Giza179 0.25 0.63 0.25 0.63 -2.45** -2.92** -1.20 -1.94** UYR 3472 × Sakha 108 -1.19 -1.03 -1.19 -1.03 5.41** 3.82** 4.60** 2.50** GZ10487 × GZ10739 -3.35** 0.40 -3.35** 0.40 -1.18 -5.64** -2.91** -0.88 GZ10487 × WAB 638-1 7.98** 8.27** 7.98** 8.27** -0.02 -1.96 -0.10 -2.87** GZ10487 × IRAT112 -10.74** -11.87** -10.74** -11.87** 2.65** 3.48* 1.54* -0.64 GZ10487 × Giza179 3.41** -4.30** 3.41** -4.30** 3.80** 2.82** 4.14** 1.02 GZ10487 × Sakha108 1.65 3.03** 1.65 3.03** -0.67 -0.44 -2.49** 0.28 GZ10739 × WAB 638-1 -8.39** -5.53** -8.39** -5.53** 3.11** -0.35 -2.30** -0.54 GZ10739 × IRAT112 -6.77** -7.33** -6.77** -7.33** 0.08 0.93 -1.63* -0.22 GZ10739 × Giza179 8.38** 2.23* 8.38** 2.23* 0.00 -0.37 0.13 -0.33 GZ10739 × Sakha108 1.61 -4.43** 1.61 -4.43** -0.91 2.34 0.84 0.27 WAB 638-1 × IRAT 112 3.89** 8.20** 3.89** 8.20** -1.36 0.04 -3.19** 0.52 WAB 638-1 × Giza179 -7.95** -3.23** -7.95** -3.23** -2.55** -1.63** -2.72** -1.48* WAB 638-1 × Sakha108 -8.72** -13.23** -8.72** -13.23** -1.75* -0.52 -2.05** -3.72** IRAT 112 × Giza179 -8.01** -7.37** -8.01** -7.37** -3.37** -3.41** -3.08** -0.43 IRAT 112 × Sakha108 -10.77 -9.70** -10.77** -9.70** -3.18** -3.37** 0.29 1.34* Giza179 × Sakha108 2.38* 6.87** 2.38* 6.87** -1.16 -0.87 2.88** 1.33* L.S.D 0.05 (sij) 2.21 1.78 2.21 1.78 1.55 1.32 1.41 1.27 L.S.D 0.01 (sij) 2.94 2.37 2.94 2.37 2.05 1.75 1.88 1.69 L.S.D 0.05 (sij-sik) 3.27 2.64 3.27 2.64 2.29 1.95 2.09 1.88 L.S.D 0.01 (sij-sik) 4.34 3.50 4.34 3.50 3.04 2.59 2.77 2.50 L.S.D 0.05 (sij-skl) 3.09 2.49 3.09 2.49 2.16 1.84 1.97 1.78 L.S.D 0.01 (sij-skl) 4.10 3.30 4.10 3.30 2.86 2.44 2.62 2.36 Table 14: Estimates of specific combining ability effects for the studied growth characters under natural and drought conditions. N: natural condition, D: drought condition. * and ** significant at 0.05 and 0.01 levels of probability, respective Acta agriculturae Slovenica, 121/2 – 2025 17 Identifying gene actions to rice yield and its components traits under both normal and drought conditions illustrated negative significant and highly significant in general combining ability under either natural and drought condition, respectively. Concerning water use efficiency four and six parents showed desirable sig- nificant and highly significant positive general com- bining ability effects under both natural and drought Table 15: Estimates of specific combining ability effects for growth characters under natural and drought conditions. N: natural condition, D: drought condition. * and ** significant at 0.05 and 0.01 levels of probability, respective Crosses Chlorophyll content (SPAD) Flag leaf area (cm2) Leaf rolling Relative water content N D N D N D N D UYR 2184 × UYR 3472 -3.27** -4.22** 0.44 3.08* -0.54 -1.28** 0.17 4.05** UYR 2184 × GZ10487 1.76 2.43** -3.43** -1.04 0.72* -0.85* -1.93* -6.32** UYR 2184 × GZ10739 0.89 0.77 -0.18 7.63** -0.14 -0.61 0.91 3.07** UYR 2184 × WAB 638-1 3.15** 7.09** 1.24 0.14 -0.24 -0.18 -2.02* -5.89** UYR 2184 × IRAT 112 0.89 1.05 -2.69** -2.73 -0.14 -0.31 -1.86* 0.47 UYR 2184 × Giza 179 4.18** 4.42** 2.41** 0.49 -0.54 -0.85* -3.79** -3.06** UYR 2184 × Sakha 108 -3.82** -4.56** 0.34 -4.17** -0.34 -0.15 1.35 6.71** UYR 3472 × GZ10487 1.38 4.50** 4.17** 3.84* 0.56 -0.91** -0.94 -2.53* UYR 3472 × GZ10739 0.61 4.47** 5.62** -1.96 0.69* -0.01 -2.74** -2.97** UYR 3472 × WAB 638-1 0.64 -1.35 -3.03** 2.86 -0.08 0.09 -0.3 -0.57 UYR 3472 × IRAT 112 5.21** 1.52 -1.95** -3.95* 0.02 0.62 1.1 -3.11 UYR 3472 × Giza179 -3.79** -1.04 -3.99** -2.13 -0.38 -0.58 -1.74 0.13 UYR 3472 × Sakha 108 3.57** -2.49** -7.32** -2.13 -0.84* -1.88** -0.39 2 GZ10487 × GZ10739 7.94** 3.73** -3.65** 1.56 -0.04 0.42 -1.44 -0.81 GZ10487 × WAB 638-1 -4.03** -3.59** -6.47** -7.16** 0.86* 1.19** -0.2 -1.04 GZ10487 × IRAT112 -2.16* -3.43** 5.38** -7.66** -0.38 1.05** 4.43** 6.59** GZ10487 × Giza179 4.80** 2.71** 5.51** 6.09** -0.78* 0.85* 6.23** 8.19** GZ10487 × Sakha108 -6.10** -2.77** -0.09 -2.51 -0.58 -0.78* -3.49** -5.87** GZ10739 × WAB 638-1 0.36 1.85* -1.48* -0.89 -0.01 0.09 -0.86 -3.41** GZ10739 × IRAT112 -3.77** -5.15** -2.71** -2.8 -0.24 -0.05 -2.10* -4.36** GZ10739 × Giza179 3.66** -1.55 -4.44** -4.18** 0.02 1.09 -1.96* -2.22** GZ10739 × Sakha108 -4.14** -2.53** -2.34** -3.71* -0.44 0.45 0.91 1.96 WAB 638-1 × IRAT 112 -0.87 3.73** 3.61** 6.42** -0.01 0.05 -1.49 0.28 WAB 638-1 × Giza179 3.99** -4.23** -4.63** -2.4 -0.08 0.19 1.21 2.25* WAB 638-1 × Sakha108 4.36** 2.19* 0.57 3.64* -0.21 -0.45 -2.08* 2.2 IRAT 112 × Giza179 -5.80** -3.84** -4.08** -1.87 0.69* 1.05** -1.93* -0.52 IRAT 112 × Sakha108 15.10** 12.68** -2.52** 0.77 0.56 -0.25 -0.12 -1.15 Giza179 × Sakha108 -5.81** -5.48** 4.15** 2.25 1.16** -0.78* 0.42 1.16 L.S.D 0.05 (sij) 1.86 1.66 1.41 2.99 0.68 0.65 1.79 2.05 L.S.D 0.01 (sij) 2.46 2.2 1.87 3.96 0.9 0.86 2.38 2.71 L.S.D 0.05 (sij-sik) 2.75 2.46 2.08 4.42 1 0.96 2.65 3.03 L.S.D 0.01 (sij-sik) 3.64 3.26 2.76 5.86 1.33 1.28 3.51 4.01 L.S.D 0.05 (sij-skl) 2.59 2.32 1.96 4.17 0.95 0.91 2.5 2.85 L.S.D 0.01 (sij-skl) 3.44 3.07 2.6 5.53 1.25 1.21 3.31 3.78 Acta agriculturae Slovenica, 121/2 – 202518 M. GABALLAH et al. conditions, respectively. On the other hand, four and two parents obtained negative significant and highly Crosses Number of panicles plant-1 1000-grain mass (g) Sterility percent- age Grain yield plant-1 (g) Water use efficiency (g ml) N D N D N D N D N D UYR 2184 × UYR 3472 1.52* 1.67** 1.77** 0.86 0.25 10.96** 4.60** 3.70** 0.09** 0.11** UYR 2184 × GZ10487 0.57 -0.41 -6.83** -3.01** 1.38* 9.75** -2.67** -4.42** -0.05** -0.13** UYR 2184 × GZ10739 -1.90** -1.37* 0.57 2.87** -2.13** -1.36 -2.14** -4.18** -0.04** -0.13** UYR 2184 × WAB 638-1 4.72** 4.54** 0.96 -0.93 1.04 -8.20** -0.08 -3.28** 0.00 -0.10** UYR 2184 × IRAT 112 1.42* 0.01 1.35* 0.61 1.42* -12.41** -0.57 -4.81** -0.01 -0.14** UYR 2184 × Giza 179 -3.00** -1.84** -1.11 0.73 -1.04 -10.94** -4.15** -0.09 -0.08** 0.00 UYR 2184 × Sakha 108 -5.40** -2.18** -0.20 -1.99** -0.96 -8.50** -2.31** -0.32 -0.04** -0.01 UYR 3472 × GZ10487 0.01 1.64** -6.04** -3.17** 1.66* 3.35** -1.63** -2.45** -0.03** -0.07** UYR 3472 × GZ10739 -3.06** -2.92** -1.01 1.91** -1.45* 0.15 -4.86** -6.27** -0.09** -0.19** UYR 3472 × WAB 638-1 0.06 -0.62 0.35 -0.69 1.32 13.84** -2.38** -3.21** -0.05** -0.10** UYR 3472 × IRAT 112 -0.44 -0.31 -2.39** -2.43** -0.17 -6.61** -0.53 -3.81** -0.01 -0.11** UYR 3472 × Giza179 -2.32** -2.86** -1.46* -1.77* 1.81** 3.10** -3.07** 0.01 -0.06** 0.00 UYR 3472 × Sakha 108 5.44** 3.90** -0.14 -2.15** -1.08 -11.90** -3.27** 0.42 -0.06** 0.01 GZ10487 × GZ10739 -1.28* -6.23** 1.99** 2.50** -0.68 -5.49** 0.74 1.57** 0.01 0.05** GZ10487 × WAB 638-1 0.07 -1.96** -2.89** -0.63 -0.05 -1.60 -1.64** 0.76* -0.03** 0.02* GZ10487 × IRAT112 2.74** 3.32** 5.47** 2.80** -0.93 0.32 -1.63** -0.60 -0.03** -0.02 GZ10487 × Giza179 3.79** 2.43** 8.51** 5.69** 0.97 9.82** 1.80** 0.92* 0.03** 0.03* GZ10487 × Sakha108 -0.38 0.12 -3.44** -2.96** 1.25 1.16 0.74 3.52** 0.01 0.11** GZ10739 × WAB 638-1 3.33** -0.05 -2.13** -4.42** 2.21** -0.61 -0.01 2.01** 0.00 0.06** GZ10739 × IRAT112 -0.13 0.62 -2.76** -5.08** 2.16** 4.95** -2.17** 2.11** -0.04** 0.06** GZ10739 × Giza179 0.12 -0.17 -1.13 1.00 0.70 -5.42** 1.03 1.83** 0.02 0.06** GZ10739 × Sakha108 -0.82 2.49** 0.59 1.66* 0.31 20.85** 3.13** 1.57** 0.06** 0.05** WAB 638-1 × IRAT 112 -1.78** -0.57 -3.11** -1.42* -1.54* 7.71** 2.52** 0.64 0.05** 0.02 WAB 638-1 × Giza179 -2.50** -1.46** -2.37** -0.26 1.43* 7.38** -1.02 1.23** -0.02 0.04** WAB 638-1 × Sakha108 -1.73** -0.40 0.14 -0.01 0.15 4.71** -1.35* 1.80** -0.03* 0.05** IRAT 112 × Giza179 -3.00** -3.12** -1.48* -3.20** 1.15 13.06** -1.11* 2.53** -0.02* 0.08** IRAT 112 × Sakha108 -2.83** -3.12** 0.87 0.29 3.16** 0.87 -2.57** 2.30** -0.05** 0.07** Giza179 × Sakha108 -1.25 -0.85 3.01** 0.78 2.40** -2.86** 4.02** -0.01 0.08** 0.00 L.S.D 0.05 (sij) 1.26 1.04 1.22 1.35 1.32 1.63 1.04 0.75 0.02 0.02 L.S.D 0.01 (sij) 1.68 1.38 1.62 1.80 1.75 2.16 1.38 1.00 0.03 0.03 L.S.D 0.05 (sij-sik) 1.87 1.54 1.80 2.00 1.96 2.40 1.54 1.11 0.03 0.03 L.S.D 0.01 (sij-sik) 2.48 2.04 2.39 2.66 2.59 3.19 2.05 1.48 0.04 0.04 L.S.D 0.05 (sij-skl) 1.76 1.45 1.70 1.89 1.84 2.27 1.46 1.05 0.03 0.03 L.S.D 0.01 (sij-skl) 2.34 1.93 2.25 2.50 2.45 3.01 1.93 1.39 0.04 0.04 Table 16: Estimates of specific combining ability effects for grain yield and its component characters under natural and drought conditions N: natural condition, D: drought condition. * and ** significant at 0.05 and 0.01 levels of probability, respective significant in general combining ability under both natural and drought condition, respectively Acta agriculturae Slovenica, 121/2 – 2025 19 Identifying gene actions to rice yield and its components traits under both normal and drought conditions 3.5 SPECIFIC COMBINING ABILITY EFFECTS (SCA): Estimates of SCA effects of all crosses for each trait under natural and drought conditions are present- ed in Table 14, 15 and 16. Regarding days to heading nine and eleven hybrids showed desirable significant and highly significant negative SCA effects under ei- ther natural and drought conditions, respectively. For plant height, ten and eleven hybrids showed desirable significant and highly significant negative SCA effects under both natural and drought conditions, respec- tively. However, ten and eleven hybrids got positive significant and highly significant in SCA under both natural and drought condition, respectively. For num- ber of tillers plant-1, five and seven hybrids showed de- sirable significant and highly significant positive SCA effects under either natural and drought conditions, respectively. Seven hybrids showed desirable signifi- cant and highly significant positive SCA under both natural and drought conditions, respectively with re- spect to panicle length. For chlorophyll content ten and eleven hybrids showed desirable significant and highly significant positive SCA effects under either natural and drought conditions, respectively. Seven and six hybrids showed desirable significant and high- ly significant positive SCA effects under either natural and drought conditions for flag leaf area, respectively. Regarding leaf rolling, five and three hybrids showed desirable significant and highly significant negative SCA effects under both natural and drought condi- tions, respectively. Two and six hybrids showed desir- able significant and highly significant positive SCA effects under either natural and drought conditions re- garding relative water content, respectively. For num- ber of panicles plant-1, seven hybrids showed desirable significant and highly significant positive SCA effects under either natural and drought conditions, respec- tively. Six hybrids showed desirable significant and highly significant positive SCA effects under both en- vironments concerning 1000-grain mass, respectively. Regarding sterility percentage, three and nine hybrids showed desirable significant and highly significant negative SCA effects under either natural and drought conditions, respectively. Regarding grain yield plant-1, 5 and 13 hybrids showed desirable significant and highly significant positive SCA effects under both en- vironments, respectively. For water use efficiency, out of 5 and 13 hybrids showed desirable significant and highly significant positive SCA effects under either natural and drought environments, respectively. 3.6 PHENOTYPIC CORRELATION COEFFICIENT: Observation values were recorded on yield con- tributing and drought tolerance characters. Data in Fig.1 The correlation coefficient at Fig.1 revealed the high significant and positive associated among grain yield and days to heading, number of tillers plant-1, panicle length, relative water content, number of pani- cles plant-1, thousand grain mass and water use effi- Fig. 1: Correlation coefficient of characteristic study under both natural and drought conditions. Acta agriculturae Slovenica, 121/2 – 202520 M. GABALLAH et al. ciency for both natural and drought environments. For days to heading, significant and highly significant positive correlation was obtained with plant height, flag leaf area, chlorophyll content, relative water con- tent, root length and grain yield plant-1. Also, highly significant negative correlation was observed with leaf rolling and sterility percentage. Plant height was significant and highly significant positive correlation was obtained with flag leaf area, chlorophyll content, relative water content and root length. Also, highly significant negative correlation was observed with leaf rolling and sterility percentage. Chlorophyll content was significant and highly significant positive correla- tion was found with flag leaf area, relative water con- tent, root length, with 100-grainmass and grain yield plant-1. Also, significant and highly significant nega- tive correlation was observed with leaf rolling and ste- rility percentage. Flag leaf area significant and highly significant positive correlation with relative water content, root length, 100-grain and grain yield plant-1. Highly significant negative correlation was observed with leaf rolling and sterility percentage. The relative water content showed significant and highly signifi- cant positive correlation with number of rootsplant-1, root length and grain yield plant-1. On the other hand, highly significant negative correlation was observed with leaf rolling sterility percentage. Leaf rolling high- ly significant positive correlation was detected with sterility percentage. On the other hand, significant and highly significant negative correlation with root length and grain yield plant-1. Concerning number of roots plant-1 had significant positive correlation with grain yield plant-1 and significant negative correlation with sterility percentage. With respect to root volume, significant and highly significant positive correlation was obtained with number of panicles plant-1, harvest index and grain yield plant-1. For root length, highly significant positive correlation was detected with grain yield plant-1 and highly significant negative cor- relation with sterility percentage. For sterility percent- age, significantly negative correlation with grain yield plant-1 and harvest index. 3.7 CLUSTERING OF GENOTYPES The heatmap and hierarchical clustering based on agronomic characteristics divided the evaluated 36 geno- types (parents and their offsprings into different clusters (Figure 2). The genotype 26, 36, 21 and 34 possessed the highest values for most of the agronomic factors (depict- ed in red) under natural condition while the genotypes 27,31 and 28 had superior in most agronomic traits at drought condition. On the contrary, the parental culti- vars 27,31,28 and 18 had the lowest values (depicted in blue) at natural irrigation otherwise the genotypes 2, 14 and 9 at drought condition. Fig. 2: Heatmap and hierarchical clustering divided the genotypes into different clusters based on the evaluated characteristics for both environments natural and drought. Red and blue colors reveal high and low values for the corresponding characteristics, respectively. Acta agriculturae Slovenica, 121/2 – 2025 21 Identifying gene actions to rice yield and its components traits under both normal and drought conditions 4 DISCUSSION Drought stress is a serious limiting factor for rice production and yield stability (Asma et al., 2021). There- fore, the achievement of modern Egyptian rice varieties with stable yield under water stress conditions would be great importance. Significant differences were ob- served among genotypes (parents, crosses, and parents vs. crosses) under drought and natural conditions for all the studied traits, implying the appreciable amount of genetic variability of the parents, crosses, and parents vs. crosses used. Thus, the evaluated genotypes could be selected for further genetic improvement on the basis of grain yield and other physiological traits under drought and natural conditions, the selected genotypes represent a scientifically robust pool for genetic improvement be- cause they address yield gap  in both stress and non-stress environments, exhibit physiological resilience (WUE, sterility control) critical for climate adaptation and en- able trait-based breeding to develop varieties with bal- anced performance. Highly significant genetic variability is present among lines, testers, and line × tester interac- tions for flag leaf area, panicle density, harvest index, biological yield per plant, and yield per plant (Saleem et al., 2010). Tiwari et al. (2011) found that parents, crosses, and parents vs. crosses are highly significant for various traits, i.e., days to 50 % flowering, effective tillers plant-1, panicle length, number of spikelets panicle-1, number of fertile spikelets, spikelet fertility percent, grain yield plant-1, Hundred grain mass, biological yield, and harvest index. Significant parents vs. crosses populations were studied for useful heterosis, which can be used to identify improved genotypes for all the traits under water stress conditions. Previous researchers have emphasized the importance of genetic variation in the breeding of new improved rice varieties (Wang et al., 2018). General com- bining ability effects (GCA) varied from the parent to an- other, giving negative or positive values. The significant values of GCA refer to genetic variance (additive) and (additive × additive) play a major role in the positive di- rection of the desired character in all the crosses in which the genotype is involved (Gaballah et al., 2021b). The negative and significant ones indicated that the flexible portion of genetic variance response well in the positive direction of desired character in some crosses and nega- tive direction in other crosses that having the genotype in question as a constant parent. So, this response would be clearly shown in the performance of the specific crosses. The non-significant (GCA) indicated that the genotypes have no important effects in the crosses in which they will be involved, but in some cases, they may show important response in specific cross which could be estimated by the (SCA). Combining ability analysis revealed signifi- cant GCA and SCA variances for all the traits under nat- ural and drought conditions, suggesting the importance of additive and non-additive gene actions in the expres- sion of these traits. GCA can be applied to identify supe- rior parental genotypes, whereas SCA helps in the iden- tification of promising hybrids that may ultimately lead to the development of hybrid populations (Saleem et al., 2010). The GCA: SCA ratio is used to identify the nature of existing gene action. The GCA: SCA ratio was less than unity for all studied traits, except for leaf rolling under natural condition indicating that the non-additive type of gene action was of greater importance in the inheri- tance of this traits, so, the selection for most traits were delay to late generation. Therefore, selection based on the accumulation of non-additive effects would be more ef- fective and successful in improving these traits in later generations. Malemba et al. (2017) revealed that in rice, the GCA:SCA for spikelet fertility, grain yield, thousand- grain mass, and panicles plant-1 are controlled by non- additive genes under drought conditions. Hybridization and then intensive selection in later generations are rec- ommended for the improvement of traits that are gov- erned by non-additive gene actions. The relatively high level of GCA variances indicated the main role of additive gene action for all traits, except leaf rolling under natural conditions. Selection and pedigree breeding methods are feasible for the improvement of rice traits governed by additive gene action (Devi et al., 2018). The significant and positive GCA effects of the parental genotypes for the studied traits are a good indication of enhancement in tolerance to drought stress conditions. The estimated GCA effects help in identifying the parental genotypes with the best genetic potential to produce individuals with desirable traits after consequent selections (Gram- aje et al., 2020). The genotypes GZ10487, GZ10739, Giza 179 and Sakha 108 were good general combiners for im- proving most traits studied under both natural and water deficit conditions. The F1 hybrids UYR 2184 × UYR 3472, GZ10487 × GZ10739, GZ10487 × Sakha108, GZ10739 × Sakha108 and WAB 638-1 × IRAT 112 were pranking populations for natural and drought tolerance and yield components. A good combination of crosses with high SCA values are ideal for heterosis breeding. The promis- ing crosses shared one of the good general combiner with drought tolerance, signifying that these crosses will even- tually yield desirable transgressive segregants (Collard et al., 2017). Positive significant heterosis over the mid and better parents was expressed by F1 hybrids viz., GZ10739 × Sakha108 and Giza179 × Sakha108 for the majority of the traits, indicating that these hybrids were found to be best suited to natural and aerobic conditions and provide desirable direction for the further improvement of toler- ance to drought stress conditions. The production of rice, Acta agriculturae Slovenica, 121/2 – 202522 M. GABALLAH et al. being the staple food in most Asian countries, has to be increased through the exploitation of heterosis breeding to meet the food security challenges of the 21st century (Prahalada et al., 2021). In the study, the association has been done to identify the nature of association among important yield contributing traits of drought tolerance with grain yield in parent and F1 generation of rice. High yield at the drought conditions has been attributed to the drought tolerance nature of the genotypes correlation analysis reveals the relationship between the various in- dependent yield contributing characters with the depen- dent variable of interest the grain yield (Acevedo-siaca et al., 2020). Also, yield improvement in drought condi- tion is difficult without understanding the association of secondary and putative traits of drought tolerance with grain yield. correlations are the magnitude of the level of association between traits (Gaballah et al., 2021a). Grain yield showed highly significant and positive correlations with the majority of the traits. The selection for one trait resulted in progress for all other traits that are positively correlated. 5 CONCLUSION The governance of yield components, including grain yield, fertility percentage, hundred grain mass, and productive tillers plant-1, by non-additive genes suggest- ed that hybridization followed by intensive selection in later generations might be effective for the further im- provement of these traits under natural and drought con- ditions. Four parents, i.e., GZ10487, GZ10739, Giza 179 and Sakha 108, were found to be good general combin- ers for yield components under natural and water stress conditions and hence could be utilized in future hybridi- zation programs for the introgression of drought toler- ance into elite rice lines. The F1 hybrids, viz., GZ10739 × Sakha108 and Giza179 × Sakha108, showed the best performance for the studied traits with desirable hetero- sis over the better parent. These promising populations could be used in future breeding program to develop natural and drought tolerant and high yielding rice geno- types. 6 DECLARATIONS Ethics approval and consent to participate Consent for publication: The article contains no such material that may be unlawful, defamatory, or which would, if published, in any way whatsoever, violate the terms and conditions as laid down in the agreement. Availability of data and material: Not applicable. Competing interests: The authors declare that they have no conflict of interest in the publication. Funding: Not applicable. Authors’ contributions: Authors MG, AE, NE, HM write the original draft and edit and finalize the manuscript. All authors read and agree for submission of manuscript to the journal. 7 ACKNOWLEDGEMENTS This publication was made possible through the support provided by Rice Research and Training Center, Egypt. 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