Effect of agrotechnical treatment on the health condition of the clonal seed ash plantation (Fraxinus excelsior L.) in the context of its infection by Hymenoscyphus fraxineus (T. Kowalski)

Ash is an important component of European forest ecosystems. In recent years the stability of the species has been threatened by the fungus Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz & Hosoya 2014 (anamorph Chalara fraxinea). Infested stands die out dynamically, and forest management does not have the seeds to restore future populations. Seed orchards may be a suitable place, where the seed can be obtained, and through which the results of immunological selection can be implemented. To reduce the infestation of seed orchards by H. fraxineus, autumn leaves that are the source of inoculum can be removed. Hence, the main aim of the study was to assess the impact of the removal of fallen leaves on the health status of clonal seed orchard of ash. The studied seed orchard is located in the Łomża Forest District (N 22.06, E 53.31), observations were made on 237 strains of 31 clones of parents. The health of ash trees based on the defoliation of crowns was assessed in August, in years 2018−2019. In order to reduce the source of H. fraxineus inoculum in the next vegetation season, an agrotechnical procedure was carried out on the orchard site to completely remove fallen ash leaves. ANOVA was used to determine the effect of this procedure on the health of ash crowns. A significant reduction in the level of defoliation (F=12.89) was demonstrated over the years of observation. The reaction of individual clones to the procedure was not uniform. The best result was obtained for clones with low and stable defoliation levels in strains. This result confirms that systematic application of agrotechnical treatment has a beneficial effect on the health and regeneration capabilities of selected clones. This result is as expected and shows the potential to carry out immunological selection of ash