Spread of dangerous walnut diseases in plantations of different ages in the Western Forest Steppe of Ukraine

Abstract

Goal. To investigate the development of the phytopathogenic complex of walnut in the Western Forest Steppe of Ukraine.
 Methods. The research was carried out during 2021—2022 in the agrocenosis of the walnut garden of the Ukrainian Research Plant Quarantine Station of the Institute of Plant Protection of the National Academy of Sciences. For a detailed account of the disease, twenty trees were examined from four sides of the crown and 25 accounting organs (leaves, shoots, fruits) were analyzed and the intensity of their damage was determined according to the scale. Diagnosis of diseases was carried out by selecting affected tissues and placing them in a moist chamber for three days for subsequent identification of the type of pathogen by microscopy and determination of systematically important morphological features of the fungus. Isolation of fungi from living plants was carried out by transferring mycelia or spores from their surface to a new environment.
 Results. A laboratory study of plant material with various symptoms of damage showed the dominance of phytopathogenic fungi: brown spotting Marssonina juglandis (Lieh.) Magn., white spotting Microstroma juglandis Sacc. and bacteriosis Xanthomonas juglandis Sacc. When surveying old tree plantations (more than 40 years old), the frequency of brown spotting of walnut Marssonina juglandis (Lieh.) Magn. accounted for 68.7%, bacterial burn (Xanthomonas juglandis Sacc.) — 31.3%. In stands of 6-year-old trees, the frequency of brown spotting Marssonina juglandis (Lieh.) Magn. was 72.5% and bacterial burn Xanthomonas juglandis Sacc. — 27.5%. When inspecting the plantations in the nursery (trees 2—3 years old), the frequency of brown spotting of the walnut Marssonina juglandis (Lieh.) Magn. accounted for 80.3% of bacterial burn Xanthomonas juglandis Sacc. — 12.1%, white spot Microstroma juglandis Sacc. — 7.6%.
 Conclusions. During the examination of walnut plantations (in trees of different ages), it was found that the high incidence of diseases, in particular, brown spotting Marssonina juglandis (Lieh.) Magn. was noted in nurseries, where on the day of the last record on susceptible forms of culture, damage by brown spot was 100.0%, while the development of the disease was 47.7%.