For horticulture in the North Caucasus, and Southern Russia as a whole, root rot of fruit crops is a serious problem, especially in nurseries and young gardens. In recent years, the harmfulness of species of the genus Fusarium Link as pathogens of root rot in the apple tree of domestic Malus domestica Borkh has been increasing. As a result of the studies, 115 samples of seedlings from four examined regions of Southern Russia were studied, 264 fungal isolates were isolated, among which 11 species of the genus Fusarium were found. The composition and occurrence of species were heterogeneous at its various sampling points. So, in the industrial gardens of the Krasnodar Territory and Karachay-Cherkess Republic, species F. sporotrichioides Sherb. and F. oxysporum Schltdl. prevailed, in the Belgorod region – F. sambucinum Fuskel, in the Rostov region -F. sporotrichioides and F. proliferatum Matsush. The most common pathogens of rotting roots of apple seedlings in the entire studied sample were: F. sporotrichioides – 81 isolates, F. proliferatum – 37 isolates and F. oxysporum – 35 isolates. The rare species among the sample were F. avenaceum – isolates, as well as the pathogens that we isolated for the first time in the region as rot pathogens of F. solani (Mart.) Sacc. and F. poae (Peck) Wollenw.

No abstract

As a result of the studies carried out, species-specific reactions of relative sensitivity to chemical fungicides of strains of the genera Fusarium Link, Alternaria Nees and Botrytis (Fr.) in vitro were noted. Fungicide Cidely-Top, DC inhibited the growth of fungi F. sporotrichioides, F. semitectum and A. alternata by 95-96 %, its minimum biological effectiveness was 83 % on the F. oxysporum strain. Fungicide Luna Tranquility, SC showed very high antifungal activity against F. avenacium, F. oxysporum and A. alternata (100 %) and low antifungal activity against F. solani and B. cinerea (73-74 %), other pathogens were suppressed with average activity. The drug Tirada, SC inhibited the growth of all studied micromycetes by 98-100 %, except for B. cinerea, the effectiveness against which was 94 % and lower. In general, against the B. cinerea fungus, the effectiveness of all drugs was average or below average, which may indicate the presence of resistance in the studied strain.

The most serious disease of the apple tree in all areas of its growth is scab. In the integrated apple tree protection system, the main method is chemical. However, the use of chemical fungicides is characterized by the risk of developing resistance to them by pathogen. The sensitivity of 118 monospore isolates of Venturia inaequalis was studied from three orchards of Jeromine, Reinette Simirenko and Gala cultivars, differing in the frequency of application of difenoconazole. Sensitivity was determined using the discriminatory dose technique (0.01 mg/l of active substance) in terms of RG, the relative growth of the mycelium. RG was expressed as the degree of change in mycelium growth in a nutrient medium with fungicide relative to the control variant in percent. All pathogen populations studied differed significantly in mean RG values. Populations treated three times per season with difenoconazole had higher RG values compared to populations treated two times. From Gala orchard, for some isolates, a stimulating effect of a discriminatory dose of difenoconazole on their growth was observed, that is, a hormesis effect was manifested. The proportion of isolates with RG values above the cutoff value, which was 84 and 100 % for the Reinette Simirenko and Gala orchards, may indicate that the pathogen populations studied are resistant, and in these orchards, there may be a decrease in the effectiveness of protection against apple scab. The discriminatory dose technique allowed us to objectively and promptly assess the sensitivity of V. inaequalis populations from orchards with varying intensity use of difenoconazole.

No abstract