Značilnosti glive Chalara fraxinea in možnosti zatiranja jesenovega ožiga : doktorska disertacija
Characteristics of the fungus Chalara fraxinea and possibilities for the control of ash dieback : doctoral dissertation

slovenian

doktorska dela

2014

Univerza v Ljubljani, Biotehniška fakulteta

Damage of ash trees caused by Chalara fraxinea was observed in nine ash seed collecting stands and in clonal plantation of narrow-leaved ash. Other harmfulorganisms and factors that influence the ash decline process were also looked for. In clonal plantation, individual resistance of ashes and defence mechanisms, such as early flushing in spring, early leaf shedding and ability to inhibit growth of pathogen in host tissue were also investigated. In laboratory experiments the temperature effect on C. fraxinea was studied, possibilities for thermal control of the pathogen were examined and different products for chemical control of the fungus were tested. Furthermore, within the group of other fungi, which were isolated from diseased ash tissue, antagonist of the pathogen was sought. Mean dead crown share in ash seed collecting stands varied between 7.2 and 38.7%, mean mortality was 1.9%. Big differences in damage between clones were observed in clonal plantation. For example, mean damaged crown share in 2012 varied between 14.2 and 83.3%. Assumed defence mechanisms were not confirmed as a cause of resistance. Fungi from genus Armillaria, namely A. gallica, A. cepistipes and A. mellea proved to be importantly involved in ash decline process. It was discovered that ash bark beetles also represent a growing threat to ashes. Laboratory experiments showed temperature interval of 20-22 °C to be optimal for pathogens growth, while temperatures above 28 °C seem to be too high for the development of the fungus. Hot water treatments of sapling and diseased shoots of common ash demonstrated that proper heat treatment (10 hours at 36-40 °C, for example) can destroy pathogen inside the host tissue without compromising the survival of saplings. Measurements of temperature in and on common ash saplings in nature demonstrated that hot summer weather periods can inhibit ash dieback development. Among eight tested fungicides, growth of C. fraxinea as well as development of Hymenoscyphus pseudoalbidus apothecia was most efficiently inhibited by the products with active ingredients carbendazim and prochloraz. Development of apothecia was successfully prevented also by the 24-hour treatment of diseased leaf petioles in 0.25% urea solution. C. fraxinea colonies in dual cultures were overgrown by 13 out of 19 tested fungi, while two additional fungi formed with C. fraxinea colonies inhibition zones. Among them, Hypocrea sp. seems to be the most suitable for the biological control ofash dieback.

26.08.2014