Acta agriculturae Slovenica, 118/4, 1–17, Ljubljana 2022 doi:10.14720/aas.2022.118.4.2234 Original research article / izvirni znanstveni članek Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) Olajoju Lola OLADOKUN 1, Dolapo Olalekan IBIRINDE 2, Adesike Oladoyin KOLAWOLE 1, 3, Charity Onye AREMU 4 Received June 04, 2021; accepted November 14, 2022. Delo je prispelo 4. junij 2021, sprejeto 14. november 2022 1 Ladoke Akintola University of Technology, Department of Crop Production and Soil Science, Ogbomoso, Nigeria 2 Federal University Wukari, Department of Crop Production and Protection, Wukari, Nigeria 3 Corresponding author, e-mail: aokolawole@lautech.edu.ng 4 Landmark University, College of Agricultural Sciences, Omu-Aran, Nigeria Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) Abstract: Tomato (Solanum lycopersicum L.) is one of the most important vegetable crops grown in Nigeria, either for fresh market or industrial purposes, necessitating the de- velopment of a robust tomato breeding programme aimed at maximizing genetic improvement on economically important traits. In this study, the combining ability, nature of gene ac- tion, heterosis, and heritability for morphological, nutritional, and physicochemical parameters of tomato were examined in five tomato parents and ten F1 offsprings, generated with a 5 × 5 half diallel mating design in the greenhouse in 2017. The field evaluation was conducted at the Teaching and Research Farm of Ladoke Akintola University of Technology, Ogbomoso, Nigeria during the cropping season of 2018 using a random- ized complete block design with three replications. Analysis of variance for combing ability revealed that both additive and nonadditive gene actions contributed to the fundamental ge- netic mechanism underlying the inheritance of the measured traits. The top two general combiner parents were UC-OP and Ib-local. Furthermore, the best tomato hybrid specific combin- ers were FDT4 × UC-OP, FDT2 × Ib-local and UC-OP × Ib-local which involved one parent having a high general combining ability effect for fruit yield and the other having other desirable traits. These hybrids may be further utilized in tomato breeding programmes. Key words: combining ability; gene action; heritability; heterosis; hybrid; tomato; variation Kombinacijske zmožnosti za morfološke in hranilne la- stnosti paradižnika (Solanum lycopersicum L.) pri dialelnem križanju Izvleček: Paradižnik (Solanum lycopersicum L.) je ena najpomembnejših vrtnin, ki se goji v Nigeriji za svežo porabo ali za industrijske namene. Za maksimiranje pridelave je po- trebno razviti robustne žlahtniteljske programe, v katerih bi izboljšali njegove genetske in ekonomske lastnosti. V raziskavi je bila preverjena kombinacijska zmožnost delovanja genov, he- teroze in dedovanja za morfološke, hranilne in fizikalno-kemij- ske lastnosti petih starševskih genotipov paradižnika in desetih F1 potomcev, pridobljenih v 5 x 5 polovičnem dialelnem kri- žanju v rastlinjaku leta 2017. Ovrednotenje v poljskem posku- su je bilo izvedeno na Teaching and Research Farm of Ladoke Akintola University of Technology, Ogbomoso, Nigeria v rastni sezoni 2018 v popolnem naključnem bločnem poskusu s tremi ponovitvami. Analiza variance za kombinacijske zmožnosti je pokazala, da je aditivno in neaditivno delovanje genov prispe- valo k osnovnim mehanizmom dedovanja merjenih lastnosti. Dva najboljša starša za komibiniranje lastnosti sta bila ‘UC-OP’ in ‘Ib-local’. Najboljša križanja za kombiniranje lastnosti so bila ‘FDT4 ’ × ‘UC-OP’, ‘FDT2 ’ × ‘Ib-local’ in ‘UC-OP’ × ‘Ib-local’, ki so vsebovala starše z velikimi splošnimi kombinacijskimi lastnostmi za pridelek plodov in druge zaželjene lastnosti. Ti hibridi bi lahko bili uporabljeni v nadaljnih žlahtiteljskih pro- gramih paradižnika. Ključne besede: kombinacijska zmožnost; delovanje ge- nov; sposobnost dedovanja; heteroza; hibrid; paradižnik; spre- menljivost Acta agriculturae Slovenica, 118/4 – 20222 O. L. OLADOKUN et al. 1 INTRODUCTION Tomato (Solanum lycopersicum L.) is one of Nige- ria’s most important vegetable crops, second only to on- ions, due to its high consumption, and is well adapted to a variety of climatic conditions, soil types, and altitudes (Osei et al., 2010). Tomatoes make an important con- tribution to human health and welfare because they are high in ascorbic acids (Vitamin C), minerals (calcium, phosphorus, and iron), and antioxidants (lycopene and β-carotene), which lower the risk of lung, breast, and prostate cancers (Willcox et al., 2003; Palozza et al., 2011; Rai et al., 2012). As a result, breeding programmes prior- itize the nutritional and physico-chemical properties of tomato fruit (Panthee et al., 2015; Acharya et al., 2018). Tomato yield is a complex character that is affected by numerous factors. It is critical to note that, due to the geometric progression of human population and the rapid rate of urbanization, which is reducing cultivable land and increasing demand for tomato, breeding for high yield alone is insufficient to meet the demands of consumers and end-users. In Nigeria, there is still a sig- nificant gap in the development of high yielding and nu- tritive tomato hybrids. Several biotic and abiotic stresses are major impediments to the successful adoption and cultivation of improved tomato varieties (Soresa et al., 2020). The Nigerian tomato market is currently saturated with mixtures of diverse cultivar that are unable to meet the numerous demands. Consequently, it has become critical to assess the genetic potential of locally available tomato cultivars for their efficient utilization and further improvement. In spite of the relatively high cost of hybrid seeds it has proven to be a successful approach for vegetable improvement (Kaushik & Dhaliwal, 2018) and usually characterized by high yield and homogeneity. Therefore, to obtain worthwhile information on the genetic makeup of cultivars useful as parental line in hybrid combina- tion, the combining ability is primarily valuable (Sprague & Tatum, 1942). General combining ability (GCA) and specific combining ability (SCA) distinguishes between the average performance of parents in crosses (GCA) and the deviation of individual crosses from the average of the parents (SCA). Additionally, GCA basically in- volves additive gene action while SCA provides genetic information on the crosses, hence elucidates the existing nonadditive gene action which offers good choice for ex- ploitation of heterosis (Ahmad et al., 2009; Senapati & Kumar 2015). The diallel mating design approach used in the expression of combining ability of lines provides information on the nature and magnitude of gene actions involved in the expression of quantitative and qualitative traits and helps to identify superior parents for hybrid development. Therefore, involving combining ability as a technique in the analysis and understanding of the ge- netic potential of parents and their hybrids is one of such possible ways in addressing tomato farmers’ and con- sumers demands. Furthermore, diallel mating designs are useful in estimating genetic parameters, which con- tributes to a better understanding of the mechanism used to predict genetic progress when parental lines are cho- sen based on their own performance (Falconer, 1989). Previous studies have used the diallel mating design to generate information on genetic parameters; GCA es- timates (Patil et al., 2013; Singh et al., 2014; Kumar et al., 2018), identification of superior cross combinations with SCA estimates (de Souza et al., 2012; Yadav et al., 2013; Saleem et al., 2013a), heterosis relative to mid parents with potence ratio (THI, 2009; Shende et al., 2012; Agar- wal et al., 2014) and heritability in broad and/or narrow sense (Osekita & Ademiluyi, 2014; Mohamed et al., 2018; Kumar et al., 2018) for diverse morphological traits in F1 tomato hybrids. Results obtained from their studies pro- vided essential information on gene actions controlling the inheritance of traits and crosses that can be utilized for developing high yielding tomato hybrid as well as for exploiting hybrid vigour. Therefore, this experiment was carried out to de- termine general and specific combining abilities effects, nature of gene action, relationships between traits, and to estimate heritability, heterosis and the mean perfor- mance for qualitative and quantitative traits of tomato cultivars crossed in a half diallel mating design. 2 MATERIALS AND METHODS The study was conducted at the Teaching and Re- search Farm of Ladoke Akintola University of Technol- ogy (LAUTECH), Ogbomoso, Nigeria and the soils are characterized as alfisol. The Global Positioning System coordinates of the experimental site was 8°10ʹ North, 4°10ʹ East, with an altitude of 341 m above sea level. The experimental site falls into the derived savanna agro- ecology of Nigeria, with annual mean rainfall of 1,100 mm and daily temperature ranges from 28–30 °C. 2.1 GENETIC MATERIALS Five tomato cultivars with different traits, FDT4 (P1), FDT2 (P2), UC-OP (P3), Ib-local (P4) and Kerewa (P5) representing the cultivars in the rain forest and de- rived savanna agro ecology of Nigeria were used in this study as the parental lines. Seeds of FDT4 and FDT2 were collected from the Federal University of Agriculture, Acta agriculturae Slovenica, 118/4 – 2022 3 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) Abeokuta (FUNAAB), Nigeria and seeds of UC-OP and Ib-local were collected from the National Horticultural Research Institute (NIHORT), Ibadan, Nigeria. Kerewa a popular commercial cultivar was collected on farmers’ field in Ogbomoso (Table 1). In the first growing season (2017), the parental tomato cultivars were grown in a greenhouse to conduct all needed crosses by hand in all possible combinations excluding reciprocals. In the sec- ond growing season (2018), tomato plants were evalu- ated on field. 2.2 NURSERY OPERATIONS In 2017 growing season, seeds of each paren- tal line were sown in nursery bed and watered regularly for six weeks. The seedlings were transplanted into a 4.5 kg soil-filled pot mixed with organic fertilizer (0.3 kg of poultry manure) in the greenhouse at six weeks after sowing and each cultivar was represented by 15 pots. The pots were laid out to fit into a diallel mating design and staking was done to keep the plants erect for easy crossing. Hybridization commenced at 7 weeks after transplanting (WAT). To achieve effective pollination, each parent lines with matured flowers that were ready to open within 24 hours were emasculated and crossed using the half diallel mating design of Griffing (1956) method II to produce the F1’s consisting of single crosses and parental lines (selfing). The pollinated flowers were carefully covered with pollinating bags and tagged for identification. The fruits from all successful pollinations were harvested at maturity and the seeds were extracted, dried and labeled for evaluation. The mating design pro- duced 15 genotypes consisting of 10 hybrid crosses and 5 parental lines from selfing. 2.3 TRIAL EVALUATION AND DATA COLLEC- TION Each of the 15 genotypes was raised as seedlings in nursery beds for six weeks and regularly watered before being transplanted to the evaluation plots. The parents (5) and F1’s (10) were evaluated on the field at the Teach- ing and Research Farm of LAUTECH in 2018, using a randomized block plot design with three replications. Each genotype was transplanted on a 5 m by 7.5 m plot with a spacing of 1 m between plots and 0.5 m between plants on a plot. N.P.K (15-15-15) fertilizer was applied at the rate of 120 kg N ha-1 three WAT. All other cultural practices, and plant protection against weeds, diseases and insects, were performed as recommended for com- mercial tomato production. Data collection commenced at 6 WAT and continued till harvesting. Data were re- corded on plant height (PH) and stem width (SW), num- ber of leaves per plant (NLPP), number of days to 50 % flowering (DTF), number of secondary branches (NSB), number of cluster per plant (CLPP), number of flower per cluster (NFPC). All harvested fruits of each plant were counted and weighed to determine number of fruits per plant (NFP), and total fruits mass per plant (FWP) measured in gram. Average fruit mass was estimated by dividing the total mass of all harvested fruits per plant by their total number. Samples of five random ripe fruits per plant were taken from all replications of each genotype to measure pericarp thickness (PCAP) in mm and number of locules per fruit (NLOBE). 2.4 NUTRITIONAL AND PHYSICOCHEMICAL ANALYSES Tomato fruit juice of each genotype was extracted from five random red ripe fruits per plant taken from all replicates. The extracted juice was filtered through dou- ble-layered muslin cloth and used for estimating total soluble solids (TSS), which was measured using a hand refractometer (RA-130-KEM, Kyoto Electronics Manu- facturing Co., Ltd., Kyoto, Japan). The readings were re- corded as oBrix (0-32 °C) at room temperature. For deter- mination of vitamin C (VIT C ) measured in mg kg-1, 10 ml of juice was diluted in 100 ml of distilled water and titrated with NaOH 0.1 N till pH 8.2. The solution was titrated with iodine (0.1 N) till changes in colour occur (IPGRI, 1996). To determine lycopene (LPEN) content (mg kg-1), 5 ml of acetone-n-hexane mixture in the ratio 4:6 was added to 0.8 g of tomato pulp for each genotype. The mix was centrifuged at 5000 rpm for 5 min at 4 °C; the supernatant was extracted and placed in spectropho- tometre (model 6400, Jenway) and scanned at 503 nm using the acetone-n-hexane mix as blank (Rosales et al., 2006). Lycopene content was quantified using an extinc- tion coefficient (E%) of 3150. All analysis was done in triplicate for each sample. 2.5 STATISTICAL ANALYSES AND ESTIMATION OF GENETIC PARAMETERS Analysis of Variance (ANOVA) was conducted and estimate of the combining ability of the genotypes were calculated using SAS (SAS institute, 2011) statisti- cal package according to Griffing’s (1956) method II, model II for half diallel analysis which assumes that the genotype and the replicate are both random variables. Acta agriculturae Slovenica, 118/4 – 20224 O. L. OLADOKUN et al. The relative importance of general combining ability (GCA) compared to specific combining ability (SCA) was calculated according to Baker (1978). If the ratio is closer to 1, it indicates predominance of additive gene ac- tion and greater predictability of progeny performance based on GCA effects (Gurmu et al., 2018). Least square mean were computed and separated using Fisher’s least significant difference (LSD) test (p < 0.05). Mid-parent heterosis was calculated for all measured traits using the formula of Mather & Jinks (1971) and the student t-statistics was used to determine the statistical differ- ence of F1 hybrid means and the mid-parent according to Wynne et al. (1970) and Kolawole et al. (2019). Potence ratio was calculated according to Smith (1952) to deter- mine the degree of dominance. Complete dominance is indicated when relative potence of gene set = +1.0; while partial dominance is indicated when the relative potence of gene set is between (-1 and +1); over-dominance is considered when potence ratio exceeds +1, whereas, the value zero, indicates absence of dominance. The positive and negative signs indicate the direction of dominance of either parent. Narrow (h2ns) and broad (H 2 bs) sense her- itabilities were determined according to Mather & Jinks (1971). Estimates of heritability were categorized as low = < 0.50, moderate = 0.50 and high = > 0.50, (Robinson et al., 1949). Phenotypic correlation coefficients were com- puted for all pairs of traits using the PROC CORR in SAS (SAS Institute, 2011). 3 RESULTS 3.1 ANALYSIS OF VARIANCE AND MEAN PER- FORMANCE There were highly significant (p < 0.001) differences in the mean squares of the tomato parental lines and hy- brids for all morphological traits, nutritional and phys- icochemical parameter measured except for number of leaves per plant (Table 2). This implied the presence of considerable genetic variation which could be exploited in tomato breeding programme. The coefficient of variation (CV) showed good experimental precisions for most of the traits meas- ured. The analysis of variance for combining ability par- titioned genetic variation into GCA and SCA. General and specific combining abilities effects showed signifi- cant (p < 0.001) additive and nonadditive gene actions influencing all traits except for stem width and number of flower per cluster for GCA and number of leaves per plant, number of days to 50 % flowering and fruit mass per plant for SCA. The comparison between the genetic variance components showed higher values of GCA than those of SCA for 8 traits. The relative importance of GCA in comparison with SCA calculated based on Baker’s Ra- tio ranged from 0.21 for number of flower per cluster to 0.93 for number of leaves per plant. The ratios were closer to unity for 9 traits out of 14, indicating the prevalence of additive gene action for plant height, number of leaves per plant, number of days to 50 % flowering, number of secondary branches, cluster per plant, pericarp thick- ness, number of locules per fruit, fruit mass per plant and vitamin C while nonadditive gene action was more important for stem width, number of flower per cluster, number of fruits per plant, lycopene and total soluble solid. The mean performance of the 15 genotypes showed wide variabilities for seven of the traits measured and some hybrids had significantly higher vigour, yield and nutritional quality than the parental cultivars. The paren- tal cultivar, Ib-local (P4) was superior for 4 morphologi- cal traits such as stem width, cluster per plant, number of flower per cluster and fruit mass per plant (Table 3). Consequently, crosses involving Ib-local (P4): FDT4 × Ib- local, UC-OP × Ib-local and Ib-local × Kerewa had the highest mean value for number of fruits per plant, num- ber of days to 50 % flowering, fruit mass per plant, cluster Genotype Source Characteristics Fruit colour FDT4 Federal University of Agriculture, Abeokuta Oblong fruit shape with two slight lobes Orange FDT2 Federal University of Agriculture, Abeokuta Rectangle fruit shape Orange UC-OP National Horticultural Research Institute, Ibadan Rectangle shape, open pollinated variety Orange Ib-local National Horticultural Research Institute, Ibadan Flat shaped fruit, average-sized with five lobes Red and yellow Kerewa Ogbomoso Oblong shape, average sized with three lobes. Pink Table 1: Description of genetic materials used in the diallel crosses Acta agriculturae Slovenica, 118/4 – 2022 5 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) per plant, tallest plant and stem width. The parental culti- var, UC-OP (P3) was superior for only three morphologi- cal traits. It had the highest number of secondary branch- es, number of fruits per plant and the thickest pericarp. F1 hybrids with UC-OP (P3) as one of the parents (FDT2 × UC-OP, UC-OP × Ib-local and UC-OP × Kerewa) had the thickest pericarp, the tallest plant and the highest fruit mass per plant. The parental cultivar, Kerewa (P5) had the highest mean value for nutritional and physic- ochemical quality, but with the lowest mean values for most of the morphological traits. Although crosses made to Kerewa (P5) which includes: FDT4 × Kerewa, FDT2 × Kerewa, UC-OP × Kerewa and Ib-local × Kerewa had the highest mean value for number of secondary branches, number of flower per cluster, vitamin C content, number of locules per fruit, cluster per plant, early flowering and stem width. The parental cultivar, FDT4 (P1) was the tall- est with the earliest flowers. Crosses involving of FDT4 (P1) such as: FDT4 × FDT2, FDT4 × Ib-local and FDT4 × Kerewa; had the highest mean value for number of leaves per plant, number of fruits per plant, number of secondary branches and number of flower per cluster. The parental cultivar, FDT2 (P2) had highest mean value only for number of leaves per plant. However Crosses of FDT4 × FDT2, FDT2 × UC-OP, FDT2 × Kerewa and FDT2 × Ib-local; had the highest number of leaves per plant and early flowering. The F1 hybrids morphological traits, nutritional and physicochemical parameters mean val- SOURCE OF VARIATION df PH (cm) SW (mm) NLPP DTF NSB CLPP NFPC REPLICATION 2 0.07 0.01 580.96 0.47 0.07 1.49 0.16 GENOTYPE 14 3.83*** 0.01*** 1688.42 17.37*** 16.99*** 16.31*** 0.85* GCA 4 5.62*** 0.004 4221.20*** 38.49*** 18.82*** 20.44*** 0.15 SCA 10 3.11*** 0.012*** 675.31 8.92 16.26*** 14.65*** 1.13** ERROR 28 0.59 0.003 889.72 4.75 0.76 1.44 0.37 CV (%) 1.45 19.89 13.13 6.44 13.32 15.18 11.31 GCA/SCA 0.78 0.41 0.93 0.90 0.70 0.74 0.21 MEAN 52.88 0.31 227.16 33.87 6.53 7.91 5.38 MINIMUM 50.30 0.16 197.33 31.33 4.67 5.33 4.67 MAXIMUM 54.50 0.42 262.00 40.33 14.33 12.67 6.33 df NFP PCAP (mm) NLOBE FMP (g) LPEN (mg kg-1) VIT C (mg kg-1) TSS (oBrix) REPLICATION 2 29.4 0.00 0.03 1024.21 0.12 0.03 0.01 GENOTYPE 14 452.00*** 0.02*** 2.82*** 2328.83* 1836.91*** 4773.07*** 3.83*** GCA 4 111.48** 0.02*** 3.57*** 5191.15** 664.32*** 5783.25*** 1.56*** SCA 10 588.21*** 0.02*** 2.53*** 1183.91 2305.95*** 4368.99*** 4.74*** ERROR 28 27.76 0.00 0.05 932.38 0.23 0.11 0.02 CV (%) 25.91 3.06 8.63 5.90 0.88 0.21 3.32 GCA/SCA 0.27 0.67 0.74 0.90 0.37 0.73 0.40 MEAN 20.33 0.55 2.67 517.47 54.05 160.23 4.61 MINIMUM 11.67 0.46 1.00 466.85 13.54 98.43 1.92 MAXIMUM   61.00 0.71 5.00 573.22 91.60 231.25 6.10 Table 2: Mean squares, general and specific combining ability for morphological traits, nutritional and physicochemical param- eters of five tomato parents and their 10 crosses *, **, *** indicates significance at 0.05, 0.01, and 0.001 probability levels, respectively GCA = general combining ability; SCA = specific combining ability; CV = Coefficient of variation PH = plant height; SW = stem width; NLPP = number of leaves per plant; DTF = number of days to 50 % flowering; NSB = number of secondary branches; CLPP = cluster per plant; NFPC = number of flower per cluster; NFP = number of fruits per plant; PCAP = pericarp thickness; NLOBE = number of locules per fruit; FMP = fruit mass per plant; LPEN= lycopene; VIT C = vitamin C; TSS= total soluble solid Acta agriculturae Slovenica, 118/4 – 20226 O. L. OLADOKUN et al. G en ot yp e PH (c m ) SW (m m ) N LP P D TF N SB C LP P N FP C N FP PC A P (m m ) N LO BE FM P (g ) LP EN V IT C TS S (o B rix ) Pa re nt s FD T 4 (P 1) 53 .0 3 0. 32 20 9. 33 31 .3 3 5. 00 5. 33 5. 67 11 .6 7 5. 20 2. 10 48 7. 51 24 .1 9 18 4. 74 5. 34 FD T 2 (P 2) 50 .3 0 0. 27 21 7. 67 34 .0 0 5. 33 5. 33 5. 00 12 .6 7 4. 80 1. 00 49 9. 26 88 .7 5 16 6. 64 1. 92 U C -O P (P 3) 52 .8 7 0. 35 20 6. 67 33 .3 3 5. 67 5. 33 5. 67 61 .0 0 5. 30 2. 00 49 4. 29 14 .2 6 20 4. 18 5. 10 Ib -lo ca l ( P 4 ) 52 .0 7 0. 42 20 7. 67 34 .0 0 4. 67 8. 00 6. 00 15 .6 7 4. 80 5. 00 51 8. 02 51 .7 8 12 7. 54 4. 22 Ke re w a (P 5) 51 .0 3 0. 20 20 1. 00 34 .6 7 5. 33 6. 00 4. 67 14 .3 3 5. 20 2. 83 46 6. 85 91 .6 0 23 1. 25 5. 82 M ea n 51 .8 6 0. 31 20 8. 47 33 .4 7 5. 20 6. 00 5. 40 23 .0 7 5. 06 2. 59 49 3. 18 54 .1 1 18 2. 87 4. 48 C ro ss es P 1 ×P 2 53 .3 3 0. 30 26 2. 00 33 .3 3 6. 00 8. 00 5. 00 16 .6 7 5. 30 2. 33 51 7. 67 57 .7 5 11 0. 69 5. 32 P 1 ×P 3 53 .1 3 0. 31 25 9. 33 33 .3 3 6. 00 11 .0 0 6. 00 17 .3 3 6. 10 2. 00 51 6. 16 42 .7 3 16 4. 67 3. 69 P 1 ×P 4 54 .0 7 0. 23 25 0. 00 33 .6 7 5. 67 9. 67 5. 33 33 .3 3 5. 60 3. 17 57 0. 95 83 .4 0 17 6. 45 5. 25 P 1 ×P 5 52 .7 0 0. 31 25 7. 33 31 .6 7 14 .3 3 8. 67 6. 33 15 .0 0 6. 60 3. 10 51 2. 35 54 .5 1 98 .4 3 4. 81 P 2 ×P 3 53 .0 0 0. 37 25 3. 00 32 .3 3 7. 67 8. 33 5. 00 15 .6 7 7. 10 2. 00 51 8. 69 57 .3 9 12 3. 66 6. 10 P 2 ×P 4 52 .8 7 0. 16 22 3. 00 33 .3 3 5. 00 11 .0 0 4. 67 17 .3 3 5. 20 2. 00 50 9. 04 76 .1 2 18 8. 44 4. 81 P 2 ×P 5 53 .4 0 0. 33 21 6. 67 31 .3 3 6. 00 6. 33 5. 00 18 .6 7 4. 60 3. 00 52 4. 84 37 .5 0 20 0. 43 3. 83 P 3 ×P 4 54 .5 0 0. 29 19 7. 33 40 .3 3 6. 00 7. 00 5. 00 18 .3 3 5. 80 2. 33 57 3. 22 55 .4 3 11 5. 13 2. 84 P 3 ×P 5 54 .4 0 0. 34 24 0. 33 38 .0 0 8. 33 6. 00 6. 00 19 .3 3 4. 90 4. 00 51 5. 43 13 .5 4 13 1. 07 5. 26 P 4 ×P 5 52 .4 7 0. 38 20 6. 00 33 .3 3 7. 00 12 .6 7 5. 33 18 .0 0 6. 30 3. 20 53 7. 75 61 .7 5 18 0. 17 4. 82 M ea n 53 .3 9 0. 30 23 6. 50 34 .0 7 7. 20 8. 87 5. 37 18 .9 7 5. 75 2. 71 52 9. 61 54 .0 1 14 8. 91 4. 67 LS D (0 .0 5) 1. 28 0. 10 49 .8 9 3. 65 1. 46 2. 01 1. 02 8. 81 0. 30 0. 39 51 .0 7 0. 80 0. 55 0. 26 Ta bl e 3: M ea n pe rf or m an ce o f p ar en ts a nd th ei r h yb rid s f or m or ph ol og ic al tr ai ts , n ut rit io na l a nd p hy sic oc he m ic al p ar am et er s PH = p la nt h ei gh t; SW = st em w id th ; N LP P = nu m be r o f l ea ve s p er p la nt ; D TF = n um be r o f d ay s t o 50 % fl ow er in g; N SB = n um be r o f s ec on da ry b ra nc he s; C LP P = cl us te r p er p la nt ; N FP C = n um be r o f flo w er p er cl us te r; N FP = n um be r o f f ru its p er p la nt ; P C A P = pe ric ar p th ic kn es s; N LO BE = n um be r o f l oc ul es p er fr ui t; FM P = fr ui t m as s p er p la nt ; L PE N = ly co pe ne (m g kg -1 ); V IT C = v ita m in C (m g kg -1 ); TS S= to ta l s ol ub le so lid Acta agriculturae Slovenica, 118/4 – 2022 7 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) ues tended to be either more than their respective mid-or better parental values with few exceptions. 3.2 ESTIMATES OF GENERAL AND SPECIFIC COMBINING ABILITIES EFFECTS The estimates of GCA effects varied among the five parental cultivar and they all showed good general com- bining abilities for diverse traits. The parental cultivars FDT4 with highly significant (p < 0.001) and positive GCA effects was considered as good general combiner only for fruit vitamin C content (Table 4). Although, two other parents viz. Kerewa and UC-OP showed highly sig- nificant (p < 0.001) and positive GCA effect for this trait as well. Moreover, for number of flower per cluster, UC-OP parental cultivar showed highly significant (p < 0.001) and positive GCA effect. Similarly, parental cultivar FDT2 showed highly significant (p < 0.001) and positive GCA effect for number of leaves per plant and fruit ly- copene content. The parental cultivar Ib-local showed highly significant (p < 0.001) and positive GCA effect for plant height, fruit mass per plant and fruit lycopene con- tent. Parental cultivar Kerewa showed highly significant (p < 0.001) and positive GCA effects for number of sec- ondary branches, cluster per plant and total soluble solid. On the other hand, considering number of days to 50 % flowering, UC-OP parental cultivar with significant (p < 0.05) and negative GCA effects was considered as good general combiner because desirable GCA effects for this trait must be negative for the development of early to- mato hybrid. Likewise, parental cultivars UC-OP, FDT2 and FDT4 with significant (p < 0.001) and negative GCA effects for number of locules per fruit were considered as good general combiners. This is because a minimal num- ber of fruit locules are desired for attractive shape and ease of processing in tomato. None of the SCA effects were significant for number of leaves per plant and fruit mass per plant (Table 5). For plant height only the cross between Ib-local × Kerewa had positive and significant (p < 0.01) SCA effect. Like- wise, only FDT4 × Ib-local had positive and highly sig- nificant (p < 0.001) SCA effect for stem width, only the F1 hybrid (FDT2 × UC-OP) had positive and significant (p < 0.05) SCA effect for number of flower per cluster and only FDT4 × UC-OP had positive and highly signifi- cant (p < 0.001) SCA effect for number of fruits per plant. Also, from the 10 F1 hybrids, two crosses (FDT2 × Kerewa and Ib-local × Kerewa) exhibited positive and highly sig- nificant (p < 0.001) SCA effects for number of secondary branches and the former reflected higher positive val- ues for SCA effect. Similarly, the crosses between FDT4 × Kerewa and FDT2 × Kerewa had positive and highly significant (p < 0.001) SCA effect for pericarp thickness and the later reflected higher positive values for SCA ef- fect. For cluster per plant, three crosses (FDT4 × Ib-local, FDT2 × UC-OP and UC-OP × Ib-local) showed positive and significant (p < 0.001) SCA effects whereas, the later reflected the highest positive values for SCA effect. The crosses FDT4 × FDT2, FDT4 × Kerewa, UC-OP × Ib-lo- cal and Ib-local × Kerewa exhibited negative and highly significant (p < 0.001) SCA effects for number of locules per fruit but FDT4 × FDT2 had the highest negative value for SCA effect. Five out of the ten F1 hybrids reflected positive and highly significant (p < 0.001) SCA effects for nutritional and physicochemical parameters. With re- spect to fruit lycopene content the best hybrid combina- tion was found to be the cross FDT4 × FDT2, which gave the highest positive value for SCA effect. Comparing the estimated SCA effects for all crosses, the cross between FDT2 × Ib-local could be considered as the best hybrid combination for vitamin C and total soluble solid since; it showed the highest and highly significant (p < 0.001) positive values for the SCA effects.   Parents TRAITS FDT4 FDT2 UC-OP Ib-local Kerewa PH (cm) -0.70*** -0.06 0.14 0.73*** -0.11 SW (mm) 0.01 -0.02 0.01 -0.01 0.01 NLPP -15.90** 20.77*** 6.96 -6.75 -5.09 DTF -0.65 -0.55 -1.03* 2.35*** -0.12 NSB -1.17*** 0.59*** -0.17 -0.50** 1.26*** CLPP -1.73*** 0.46 0.41 0.17 0.70** NFPC 0.06 0.06 -0.13 -0.04 0.06 NFP 0.71 -1.48 3.38*** 0.05 -2.67** PCAP (mm) -0.04*** 0.01** 0.03*** -0.02*** 0.01*** NLOBE -0.14*** -0.30*** -0.43*** 0.40*** 0.47*** FMP (g) -21.63*** 4.18 -3.30 22.15*** -1.41 LPEN (mg kg-1) -4.22*** 8.66*** -5.56*** 1.63*** -0.52*** VIT C (mg kg-1) 19.67*** -19.12*** 6.24*** -15.38*** 8.59*** TSS (oBrix) 0.01 -0.19*** 0.28*** -0.35*** 0.24*** Table 4: Estimates of the GCA effects of five tomato parents for morphological traits, nutritional and physicochemical parameters *, **, *** indicates significance at 0.05, 0.01, and 0.001 probability levels, respectively PH = plant height; SW = stem width; NLPP = number of leaves per plant; DTF = number of days to 50 % flowering; NSB = number of secondary branches; CLPP = cluster per plant; NFPC = number of flower per cluster; NFP = number of fruits per plant; PCAP = pericarp thickness; NLOBE = number of locules per fruit; FMP = fruit mass per plant; LPEN= lycopene; VIT C = vitamin C; TSS= total soluble solid Acta agriculturae Slovenica, 118/4 – 20228 O. L. OLADOKUN et al. 3.3 BROAD-SENSE (H2) AND NARROW-SENSE (h2) HERITABILITIES ESTIMATES Broad sense heritability estimates ranged from 0.28 for number of leaves per plant to 1.00 for lycopene and vitamin C (Table 6). The estimates were high for plant height, stem width, number of secondary branches, clus- ter per plant, number of fruits per plant, pericarp thick- ness, lycopene, vitamin C and total soluble solid, indi- cating low environmental influence. The remaining five traits had low broad sense heritability estimates. Narrow sense heritability estimates ranged from 0.04 for number of secondary branches to 0.50 for pericarp thickness. The estimates were relatively low for number of leaves per plant, number of secondary branches, cluster per plant, number of flower per cluster and vitamin C whereas, stem width, number of days to 50 % flowering, pericarp thickness, lycopene and total soluble solid had moderate narrow sense heritability estimates, suggesting their importance in enhancing selection. 3.4 HETEROSIS AND POTENCE RATIO ESTI- MATES OF TOMATO F1 HYBRIDS All the traits showed either or both significant posi- tive or negative heterosis in different crosses, thereby reflecting that the parental cultivars are genetically di- verse for traits measured except for number of secondary branches and pericarp thickness (Table 7). Mid-parent heterosis estimates for plant height were significant and positive for the ten tomato F1 hybrids, and the highest (5.4 %) was observed for FDT2 × Kerewa. The potence ratios for plant height ranged from 0.7 to 7.5, with nine crosses indicating overdominance and one indicating partial dominance in the inheritance of this trait. Simi- CROSS PH (cm) SW (mm) NLPP DTF NSB CLPP NFPC   FDT4 × FDT2 -1.82 *** -0.03 -14.37 1.33 -0.62 -1.30* -0.49 FDT4 × UC-OP 0.55 0.03 -11.56 1.14 0.48 -1.25 * 0.37 FDT4 × Ib-local -0.84 * 0.12*** 3.16 -1.57 -0.19 1.65** 0.60 FDT4 × Kerewa 0.54 -0.13 *** 8.79 0.33 -0.48 0.02 -0.65* FDT2 × UC-OP 0.17 0.01 4.44 1.05 -0.95 * 2.22*** 0.70* FDT2 × Ib-local 0.51 -0.04 8.83 -2.00 -0.95 * 1.13 -0.06 FDT2 × Kerewa 0.56 0.03 7.79 -0.95 4.24 *** -1.22* 0.35 UC-OP × Ib-local -0.89* -0.14*** -4.37 -1.86 -0.86 2.51*** -0.54 UC-OP × Kerewa 0.33 0.05 -0.44 -0.86 -0.14 -3.08*** -0.41 Ib-local × Kerewa 1.06** 0.05 8.70 3.67** 1.52*** -4.03*** 0.30 NFP PCAP (mm) NLOBE FMP (g) LPEN (mg kg-1) VIT C (mg kg-1) TSS (oBrix) FDT4 × FDT2 -6.90 *** -0.04*** -1.23*** -0.76 30.27*** 5.85*** -2.51*** FDT4 × UC-OP 36.57 *** -0.02* -0.10 1.75 -30.02*** 18.04*** 0.20* FDT4 × Ib-local -5.43 * -0.02** 2.07*** 0.02 0.32 -36.99*** -0.05 FDT4 × Kerewa -14.14 *** 0.04*** -0.46*** -14.30 20.86*** 27.92*** 1.66*** FDT2 × UC-OP -0.71 0.02 0.06 -2.19 -14.42 *** 17.32*** -1.01*** FDT2 × Ib-local -4.90 0.01 0.39 *** 27.15 19.06*** 50.71*** 1.18*** FDT2 × Kerewa -1.90 0.05 *** 0.52*** -16.04 -21.29*** -62.58*** 1.24*** UC-OP × Ib-local -6.43* -0.05*** -0.64*** -27.28 26.00*** 37.35*** 0.27*** UC-OP × Kerewa -13.81*** -0.04*** 0.48*** 19.90 3.98*** -23.67*** -0.38*** Ib-local × Kerewa -0.48 -0.003 -0.68*** -11.34 -43.51*** -36.72*** -0.32***   Table 5: Estimates of the SCA effects involving morphological traits, nutritional and physicochemical parameters of 10 tomato crosses derived from a 5 × 5 half diallel *, **, *** indicates significance at 0.05, 0.01, and 0.001 probability levels, respectively PH = plant height; SW = stem width; NLPP = number of leaves per plant; DTF = number of days to 50 % flowering; NSB = number of secondary branches; CLPP = cluster per plant; NFPC = number of flower per cluster; NFP = number of fruits per plant; PCAP = pericarp thickness; NLOBE = number of locules per fruit; FMP = fruit mass per plant; LPEN= lycopene; VIT C = vitamin C; TSS= total soluble solid Acta agriculturae Slovenica, 118/4 – 2022 9 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) Traits Narrow-sense Heritability Broad-sense Heritability PH (cm) 0.14 0.66 SW (mm) 0.21 0.57 NLPP 0.08 0.28 DTF 0.25 0.49 NSB 0.04 0.88 CLPP 0.08 0.77 NFPC 0.09 0.42 NFP 0.15 0.87 PCAP (mm) 0.50 0.95 NLOBE 0.10 0.33 FMP (g) 0.13 0.33 LPEN (mg kg-1) 0.22 1.00 VIT C (mg kg-1) 0.09 1.00 TSS (oBrix) 0.25 0.99 Table 6: Narrow and broad sense heritability for morpho- logical traits, nutritional and physicochemical parameters of tomato PH = plant height; SW = stem width; NLPP = number of leaves per plant; DTF = number of days to 50 % flowering; NSB = number of sec- ondary branches; CLPP = cluster per plant; NFPC = number of flower per cluster; NFP = number of fruits per plant; PCAP = pericarp thick- ness; NLOBE = number of locules per fruit; FMP = fruit mass per plant; LPEN= lycopene; VIT C = vitamin C; TSS= total soluble solid larly, fruit mass per plant reflected desirable positive mid parent heterosis for the ten tomato F1 hybrids, and the highest (13.7 %) was observed for FDT4 × Ib-local. The potence ratios for fruit mass per plant ranged from -8.8 to 3.4 with nine crosses indicating overdominance and one cross combination (FDT2 × Ib-local) indicating no dominance in the inheritance of this trait. For number of leaves per plant, a positive heterosis is desirable and was estimated for nine F1 hybrids, and the highest (25.7 %) was observed for FDT4 × UC-OP. These results were also confirmed by potence ratios, which had positive/negative values, indicating the presence of partial to over domi- nance effects. Regarding number of leaves per plant, 9 F1 hybrids exhibited significant positive heterosis over mid parent and only the cross between UC-OP × Ib-local had significant negative heterosis but was also the only hybrid with significant positive heterosis over mid parent for cluster per plant. The potence ratios for number of leaves per plant ranged from -11.6 to 49.8 with eight crosses indicating overdominance and two indicating partial dominance in the inheritance of this trait whereas, the potence ratios for cluster per plant indicates partial dom- inance. For number of days to 50 % flowering, a negative heterosis is desirable and was estimated for half of the tomato F1 hybrids, and the lowest (-8.7 %) was observed for FDT2 × Kerewa indicating earliness, supported by the potence ratios signifying partial to over dominance ef- fects. The estimates of heterosis, relative to mid parental values reflected significant mid parent heterosis but with only negative signs, on five and four tomato F1 hybrids for number of flower per cluster and number of fruits per plant respectively, indicating the presence of the various degree of recessiveness involved in the inheritance of the two traits. This result was also confirmed by the potence ratios, which appeared with negative values for most of the hybrids. The range of significant mid parent heterosis in the desired direction for nutritional parameters var- ied from 2.3 to 28.1 % with the maximum (11.4 %) for lycopene content being found in FDT2 × UC-OP while the best hybrid for tomato vitamin C content was FDT2 × Ib-local with mid parent heterosis estimate of 28.1 %. These results were further confirmed with the potence ratios which were majorly described by partial to over dominance effects. 3.5 PHENOTYPIC CORRELATIONS BETWEEN TRAITS Fruit mass per plant was significant (p < 0.01) and positively correlated with plant height (r = 0.46), number of days to 50 % flowering (r = 0.34) and cluster per plant (0.34) (Table 8). Number of flower per cluster had a sig- nificant (p < 0.01) positive association with stem width (r = 0.45) and number of secondary branches (r = 0.38). A positive and significant (p < 0.01) correlation was observed between number of secondary branches and number of leaves per plant (r = 0.39). Number of locules per fruit also showed significant (p < 0.05) and positive correlation with stem width (r = 0.30) and number of flower per cluster (r = 0.33). On the other hand, corre- lation between the nutritional parameters and morpho- logical traits were significant (p < 0.01) but negative, with correlation coefficient ranging from -0.30 to -0.51. 4 DISCUSSION The significant variation among the tomato paren- tal lines and their F1 hybrids for all traits except number of leaves per plant shows inherent variability among the parental cultivars which support the report of Saleem et al. (2013b) and Kumar et al. (2018). These variations al- lowed combining ability analysis (Singh & Chaudhary, 1977). Considering all the traits measured in this study, Acta agriculturae Slovenica, 118/4 – 202210 O. L. OLADOKUN et al.   Crosses FDT4 × FDT2 FDT4 × UC-OP FDT4 × Ib-local FDT4 × Kerewa FDT2 × UC-OP Parameters TRAITS MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio PH (cm) 3.2** 1.2 0.3** 2.2 2.9** 3.1 1.3** 0.7 2.8** 1.1 SW (mm) -0.6 -0.1 -7.4 1.7 -37.5** 2.8 20.5 0.8 18.1 1.4 NLPP 22.7** -11.6 24.7** 38.5 19.9** 49.8 25.4** 12.5 19.3** -7.4 DTF 2.0** -0.5 3.1** -1.0 3.1** -0.8 -4.0** 0.8 -4.0** 4.0 NSB 16.1 -5.0 12.5 -2.0 17.2 5.0 177.4 -55.0 39.4 13.0 CLPP 50.0 0.0 106.3 0.0 45.0 -2.3 52.9 -9.0 56.3 0.0 NFPC -6.3** -1.0 5.9 0.0 -8.6** 3.0 22.6 2.3 -6.3** -1.0 NFP 36.9 -9.0 -52.3** 0.8 143.9 -9.8 15.4 -1.5 -57.5** -0.9 PCAP (mm) 5.9 1.5 15.8 -25.0 12.0 2.6 27.6 43.0 39.5 8.6 NLOBE 50.5 1.4 -2.4 -1.0 -10.8** 0.3 25.7 -1.7 33.3 1.0 FMP (g) 4.9** -4.1 5.2** -7.5 13.7** -4.5 7.4** 3.4 4.4** -8.8 LPEN (mg kg-1) 2.3** -0.1 122.3 4.7 119.6 -3.3 -5.9** 0.1 11.4** -0.2 VIT C (mg kg-1) -37.0** -7.2 -15.3** 3.1 13.0** 0.7 -52.7** 4.7 -33.3** -3.3 TSS ( oBrix ) 46.7 1.0 -29.3** -12.7 9.9 0.9 -13.8** 3.2 74.0 1.6 Crosses FDT2 × Ib-local FDT2 × Kerewa UC-OP × Ib-local UC-OP × Kerewa Ib-local × Kerewa Parameters TRAITS MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio MPH (%) Potence ratio PH (cm) 3.3** 1.9 5.4** 7.5 3.9** 5.1 4.7** 2.7 1.8** 1.8 SW (mm) -54.1** -2.5 39.0 -2.4 -26.2* 2.9 23.6 0.8 21.5 0.6 NLPP 4.9** -2.1 3.5** -0.9 -4.8** 19.7 17.9** 12.9 0.8** 0.5 DTF -2.0** 0.0 -8.7** -9.0 19.8** -20.0 11.8** -6.0 -2.9** 3.0 NSB 0.0** 0.0 12.5 0.0 16.1 1.7 51.5 17.0 40.0 -6.0 CLPP 65.0 3.3 11.8 2.0 5.0** -0.3 5.9 -1.0 81.0 5.7 NFPC -15.2** -1.7 3.5 -1.0 -14.3** 5.0 16.1 1.7 0.0 0.0 NFP 22.4 2.1 38.3 6.2 -52.2** -0.9 -48.7** -0.80 20.0 4.5 PCAP (mm) 9.0 -13.0 -7.3 -2.2 15.2 2.9 -7.0 -5.5 26.9 -6.7 NLOBE -33.3** -0.5 56.5 1.2 -33.3** 0.8 65.5 -3.8 -18.3** -0.7 FMP (g) 0.1** 0.0 8.7** -2.6 13.3** -5.7 7.3** 2.5 9.2** 1.8 LPEN ( mg kg-1) 8.3** -0.3 -58.4** -37.1 67.9 -1.2 -74.4** 1.0 -13.9** 0.5 VIT C ( mg kg-1) 28.1** -2.1 0.8** 0.1 -30.6** -1.3 -39.8** 6.4 0.4** -0.0 TSS ( oBrix ) 56.9 1.5 -1.0 -0.0 -39.0** -4.1 -3.7 0.6 -3.9 0.3 Table 7:Estimates of percent mid-parent heterosis and potence ratios for morphological traits, nutritional and physicochemical parameters of 10 tomato crosses MPH = Mid-parent heterosis *, **Significantly different from mid-parent at 0.05 and 0.01 probability levels, respectively, using t-test Acta agriculturae Slovenica, 118/4 – 2022 11 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) the significant differences exhibited by GCA variance for number of leaves per plant, number of days to 50 % flowering and fruit mass per plant implies that only these three traits are controlled solely by additive gene action and the decision to improve those traits would be effec- tive in early generations (Avdikos et al., 2021). The pre- ponderance of additive variance in expression of mor- phological traits has been reported by Singh et al. (2010), Farzane et al. (2012), Shalaby (2013) and Vekariya et al. (2019). On the other hand, the exclusive significance of SCA variance for stem width and number of flower per cluster showed supremacy of nonadditive gene action the main cause of heterosis (Burdick, 1954) in the inherit- ance of these traits in agreement with the reports of (Go- vindarasu et al., 1981; Shankar et al., 2013). The significance of both GCA and SCA variances for plant height, number of secondary branches, cluster per plant; number of fruits per plant, pericarp thick- ness, number of locules per fruit, lycopene, vitamin C and total soluble solid indicate the joint role of both ad- ditive and non-additive gene action which corroborate the report of Singh et al. (2010), Kumar et al. (2018) and Dufera et al. (2018). The magnitudes of GCA variances were higher than those of SCA variance for seven traits. Also, the ratio of GCA: SCA was greater than unity for those traits, indicating the preponderance of additive gene action in their inheritance (Christie & Shattuck, 1992). This is in agreement with Bakers’ predictability ratio as the ratios for these traits were greater than 0.50. Therefore, selection for these traits could be an effective breeding approach in tomato improvement programmes.   PH (cm) SW (mm) NLPP DTF NSB CLPP NFPC NFP NLOBE FMP (g) LPEN (mg kg-1) SW 0.10                     NLPP 0.26 -0.08                   DTF 0.11 -0.13 -0.18                 NSB 0.11 0.18 0.39** -0.08               CLPP 0.12 -0.11 0.29* -0.06 0.11             NFPC 0.10 0.45*** 0.14 -0.09 0.38** 0.01           NFP 0.13 0.07 -0.17 0.06 -0.15 -0.12 0.09         NLOBE 0.18 0.30* -0.06 0.15 0.16 0.13 0.33* -0.06       FWP 0.46*** 0.09 0.17 0.34* 0.10 0.34* 0.00 -0.01 0.15     LPEN -0.44*** -0.47*** 0.00 -0.01 -0.13 0.28 -0.42*** -0.33* -0.19 0.07   VIT C -0.30* -0.30* -0.35* -0.22 -0.51*** -0.10 -0.28 0.28 -0.21 -0.30* 0.13 Table 8: Pearson’s correlation coefficients (r) between tomato morphological traits and nutritional parameters *, **, *** indicates significance at 0.05, 0.01, and 0.001 probability levels, respectively PH = plant height; SW = stem width; NLPP = number of leaves per plant; DTF = number of days to 50 % flowering; NSB = number of secondary branches; CLPP = cluster per plant; NFPC = number of flower per cluster; NFP = number of fruits per plant; NLOBE = number of locules per fruit; FMP = fruit mass per plant; LPEN= lycopene; VIT C = vitamin C (mg kg-1) In addition, since GCA variances are higher than SCA variances, early generation selection of genotypes based on those traits becomes more efficient and promising hy- brids can be identified (Smith et al., 2008). Conversely, the magnitude of SCA variances were higher than those of GCA variance for stem width, number of flower per cluster, number of fruits per plant, lycopene and total sol- uble solid as reported earlier (Farzane et al., 2012; Shende et al., 2012; de Souza et al., 2012; Yadav et al., 2013). Be- sides, the bakers’ ratios were below 0.50 for these traits indicating the preponderance of nonadditive gene action in their inheritance (Christie & Shattuck, 1992). Thus, hybrid vigour can be exploited considering these traits in a tomato breeding programme but selection of superior genotypes may be delayed till later generations when the genes are fixed in the homozygous lines (Geleta & La- buschagne, 2006). Out of the 14 traits measured, the overall parental mean value were significantly lower than the hybrids mean value for number of leaves per plant, number of secondary branches, cluster per plant, number of fruits per plant, fruit mass per plant and vitamin C which re- vealed an overall improvement in those traits through hybridization. It is important to mention that the paren- tal lines and their offspring had similar gene for plant height which varied only by 2.9 %, as they both displayed the determinate growth habit. Additionally, the observed high number of leaves per plant was mainly because the data was collected at maturity which corroborates the re- port of Ibitoye et al. (2000). On the other hand, Ngosong et al. (2017) reported between 15 and 30 leaves per plant Acta agriculturae Slovenica, 118/4 – 202212 O. L. OLADOKUN et al. but at three weeks after planting which implies that the stage of plant maturity determines the number of leaves. Thakur et al. (2017) and Vieira et al. (2019) previously described pericarp mean thickness for ripe tomatoes ranging between 4.1mm and 7.6mm, correlating with the value obtained in this study. The wide range for vitamin C observed in this study was in consonance with the report of Rivero et al. (2022) who reported 115.7 to 178.5 mg kg−1 in tomato cultivars commercialized in Cuba. With the exception of stem width, comparing the mean per- formance of the ten F1 hybrids and their parental cultivar for other measured traits shows that more than eight of the hybrids tended to be either higher than their respec- tive lower parent or deviated towards the higher parent. Superiority reflected by these hybrids was in agreement with the report of Pradeepkumar et al. (2001) and Han- nan et al. (2007). The estimations of general and specific combining abilities provided information on the breeding potential of the five tomato parents and their F1 crosses. In crop im- provement programmes, an astute selection of parental lines promotes a well-planned hybridization programme, and a parent with higher positive significant GCA effects (depending on the desired direction per trait) is consid- ered a good general combiner. The estimates of significant GCA effects in the desired direction shows the reflection of the parental cultivars potential to transfer the traits to their progeny (Gayosso-Barragán et al., 2019). The pa- rental cultivar UC-OP had the most significant GCA ef- fects, with 5 traits in the desired direction, followed by FDT2 and Kerewa with 4 traits each. By ranking the five parents according to the GCA effects, only Ib-local can be identified as promising general combiners for fruit mass per plant and plant height. Likewise, only FDT2 was identified as general combiner for number of leaves per plant. Also, only Kerewa was superior general combiners for secondary branches and cluster per plant and UC-OP combines well for early flowering, number of fruits per plant and number of locules per fruit. Considering more than a parent with significant GCA effects in the desired direction for some traits; the parental cultivars FDT2 and Ib-local seems to be better general combiners for lyco- pene. The parental cultivars, FDT4, Kerewa and UC-OP were promising general combiners for vitamin C, Kerewa and UC-OP were identified as superior general combin- ers for total soluble solid while FDT2, UC-OP and Kerewa are good combiner for pericarp thickness which makes them suitable for industrial use. These two parents (FDT2 and FDT4) also combine well for number of locules per fruit. Hence, the five parents were general combiners for diverse traits. Parents with high GCA effects for multiple traits could be used in breeding programmes to develop tomatoes with different combinations of traits because favourable additive genes would have accumulated (Ba- hari et al., 2012). Previous studies have reported signifi- cantly positive GCA effects for number of branches per plant (Singh and Nandapuri, 1974), number of fruits per plant (Dharmatti, 1996), plant height (Patil, 2013), fruit mass (Singh et al., 2014) and total soluble solid (Kumar et al., 2018) in tomato in spite of the different parents and environments used in their studies. High and positive SCA effect estimates reveal the best combiner among the parental cultivars for the de- velopment of hybrids with specific target traits (Peña et al., 1998). All the hybrid combinations were found to be good specific combiners for a minimum of two traits, indi- cating the significant role of nonadditive gene action in the inheritance of these traits. Tomato is a self-polli- nated crop; hence SCA effect may not contribute much to improvement of traits but cross combinations with SCA in the desired direction coupled with good GCA may be utilized in breeding programmes (Wamm et al., 2010; Rewale et al., 2003). In this study, all cross com- binations showed at least one desirable SCA effect, and none of the hybrids showed significant SCA effects for all traits. Tomato F1 hybrids viz. UC-OP × Ib-local was the best specific combiners with the highest number of traits. The cross combinations between FDT4 × FDT2, FDT4 × UC-OP, FDT4 × Kerewa and UC-OP × Ib-local exhibited highly significant positive SCA effects for some morphological traits, nutritional and physicochemical parameters. According to Singh & Narayanan (1993) SCA effect refers to non-additive gene action which has positive relationship with heterosis. Therefore, hybrids FDT4 × UC-OP, FDT2 × Ib-local and UC-OP × Ib-local which involves one parent with a high GCA effect for number of fruits per plant and fruit mass per plant may be considered useful for the improvement of fruit yield, lycopene, vitamin C and total soluble solid and heterosis breeding may be recommended (Saleem et al., 2013a). These hybrids would be expected to produce segregants of a fixable nature in segregating generations through the simple pedigree method (Pandiarana et al., 2015). Heritability estimates indicate the reliability with which traits can be passed down from one generation to the next. Estimates of broad-sense heritability were high for most of the traits measured indicating that the varia- tion observed for those traits are genetically determined and the effect of environment on them were low, hence selection based on phenotypic expression will be effi- cient for genetic improvement of these traits. Moreover, selection for these traits at early segregating generation could lead to selection of elite genotypes (Bozokalfa et al., 2010). The broad-sense heritability estimates obtained in this study are in agreement with earlier reports (Haydar Acta agriculturae Slovenica, 118/4 – 2022 13 Combining ability for morphological and nutritional traits in a diallel cross of tomato (Solanum lycopersicum L.) et al., 2007; Sanjeev, 2010; Osekita & Ademiluyi, 2014; Kumar et al., 2018; Mohamed et al., 2018). Low narrow- sense heritability estimates for plant height, number of leaves per plant, number of secondary branches, clus- ter per plant, number of flower per cluster, number of fruits per plant, number of locules per fruit, fruit mass and vitamin C showed that they are primarily controlled by non-additive genes, and that selection for these traits may be ineffective. The nature and magnitude of heterosis estimates help in the identification of promising hybrids (Pandi- arana et al., 2015). The entire cross combinations were prominent for displaying highly significant heterosis over mid parent for only plant height and fruit mass per plant with the presence of various degrees of over domi- nance effects indicating the inherent genetic diversity between the parental cultivars and the newly developed hybrids that can be exploited through selection. This cor- roborates the report of previous researcher who found positive and significant heterosis for plant height and fruit mass per plant (Mageswari et al., 1999; Kurian et al., 2006; Shende et al., 2012; Agarwal et al., 2014). Thus, the best hybrid for plant height was FDT2 × Kerewa (5.4 %) and superior hybrids for fruit mass per plant were FDT4 × Ib-local (13.7 %) and UC-OP × Ib-local. Number of leaves per plant had mostly significant positive heterosis over mid parent with partial to over dominance effects. Out of 10 tomato F1’s, only one cross (UC-OP × Ib-local) expressed significant and positive heterosis with partial dominance for cluster per plant. The fewer the number of tomato locules the better for proper shape, firmness, pro- cessing, concentrations of solids and ascorbic acid (Dun- di & Madalageri, 1991; Thamburaj, 1998). Heterosis in the negative direction with partial dominance effect with cross combinations FDT2 × Ib-local and UC-OP × Ib- local (-33.3 %) are desirable hybrids for number locules per fruit. Considering the nutritional parameters, high lycopene and vitamin C are essential in the development of quality tomato because they add value to processed products as quality requirements desired by the consum- ers. Positive mid-parent heterosis estimates on few F1 hy- brids for lycopene and vitamin C found in this study were higher than the report of Pandiarana et al. (2015). These results were further confirmed with the potence ratios indicating partial to over dominance effects in the inher- itance these parameters. Previous studies have reported significant positive heterosis for lycopene (YongFei et al., 1998), vitamin C (Makesh, 2002) and significant nega- tive heterosis for number of locules per fruit (Sekhar et al., 2010). Early flowering in tomato is a desirable char- acter; therefore negative heterosis is preferred over posi- tive heterosis. Half of the cross combinations displayed significant negative heterosis over mid parent and the hybrids; FDT2 × Kerewa depicted maximum significant negative heterosis. These results were strongly supported by the potence ratios, with two crosses each indicating partial to over-dominance effects, coupled with one cross combination signifying no dominance in the inheritance of this trait. Significant negative heterosis estimates were observed in the hybrids for number of fruits per plant and number of flower per cluster contrary to previous reports of Hannan et al. (2007). Various degrees of domi- nance were involved in the inheritance of the morpho- logical and nutritional traits of tomato measured in this study and the negative values of potence ratio illustrated the presence of various degrees of recessiveness. Based on the significant percent mid parent heterosis estimate there is a potential to develop hybrids that are taller, early flowering, with fewer lobes, more number of leaves per plant, increased fruit mass per plant, higher lycopene and vitamin C content. In agreement with these findings, previous studies have reported significant performance of tomato hybrids above the parental lines (Singh et al., 2006; Dar et al., 2011; Singh et al., 2014; Pandey et al., 2015; Senapati & Kumar 2015). Correlations between traits are critical in improving the efficiency of breeding programmes and assisting with appropriate selection indices (Nzuve et al., 2014). The positive relationship between fruit mass per plant, plant height, number of days to 50 % flowering, and cluster per plant is desirable, and it suggests that selecting taller to- mato plants may result in larger fruits due to the stem re- serve mobilization mechanism (Al-Tabbal & Al-Fraihat, 2012). Also, late flowering selection results in higher fruit yield and an increased number of tomato fruits due to a higher number of clusters per plant. Furthermore, the correlation between the number of flowers per cluster and the stem width and number of secondary branches, as well as the correlation between the number of leaves per plant and the number of secondary branches, show that traits with similar physiology were correlated and may be used for indirect selection. The relationship be- tween the number of locules per fruit and stem width and the number of flowers per cluster suggests that se- lecting for a wider stem and flower cluster improves the capacity to support tomato fruits with many locules. According to Mitchel et al. (1991) and Agong et al. (1997) nutritional and physicochemical properties are used as criteria to judge the organoleptic and process- ing qualities of tomato. Highly significant and negative correlations found between morphological traits and lycopene and even vitamin C corroborate the report of Agong et al. (2001) indicating that breeding programme would have to compromise some morphological traits to obtain better quality, particularly when nutrition is included as objectives in breeding programmes. On the Acta agriculturae Slovenica, 118/4 – 202214 O. L. OLADOKUN et al. contrary, Kaushik & Dhaliwal (2018) reported lack of significant correlations between morphological traits and biochemical traits. 5 CONCLUSION The half diallel analysis technique revealed the relative breeding potential of the parental cultivars and superior good combiner parents. The results from this study clarifies the nature and magnitude of gene action involved in the inheritance of the traits measured, pro- vided information on the genetic worth of parental lines and possibility of selecting superior hybrids for further exploitation. The combining ability study confirms the presence of high variation among the genotypes with the preponderance of both additive and nonadditive gene ac- tions influencing the inheritance of morphological traits, nutritional and physicochemical parameters measured. Parental line Ib-local was identified as potential donor for plant height, fruit mass, fruit lycopene content and UC-OP was superior for earliness, fruits per plant, num- ber of locules per fruit, fruit vitamin C content. These two parents may be useful in tomato improvement pro- grammes. Three promising hybrids (FDT4 × UC-OP, FDT2 × Ib-local and UC-OP × Ib-local) were selected on the basis of involvement of one parent with a high GCA effect for number of fruits per plant and fruit mass per plant, relevance of SCA effects and heterosis. These cross combinations may be considered useful for the improve- ment of fruit yield, lycopene, vitamin C and total solu- ble solid contents. The selected superior tomato hybrid may be released as varieties to growers for commercial cultivation. The findings of this study could be used to determine the best approach for tomato improvement in a breeding programme. 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