This study analyzed the species composition and population structure of phytopathogenic fungi in short-rotation sugar beet agrocenoses of the Western Forest-Steppe of Ukraine. Based on 150 samples (90 roots and 60 rhizosphere soil samples) collected from fields of PE “Zakhidnyi Buh”, a total of 240 fungal isolates were identified. The dominant taxa included Fusarium oxysporum, F. solani, Phoma betae, Rhizoctonia solani, and Botrytis cinerea, accounting for more than 90% of the rhizosphere mycobiota. The genus Fusarium was the most abundant (48 ± 3.5%), forming a stable infectious core of the agroecosystem. Short-rotation crop sequences (wheat-soybean-beet and maize-soybean-beet) were found to increase the isolation frequency of F. oxysporum by 25–30% and Phoma betae by 18–22% compared with other systems, while the share of Rhizoctonia solani in rotations with maize reached 16%. Soil type significantly influenced the species profile: F. oxysporum predominated in calcareous sandy soils (≈35%), whereas F. solani and P. betae were dominant in chernozems. Morphological variability of Fusarium isolates (pigmentation and sporulation level of 2.5×10⁵–1.8×10⁶ spores mL⁻¹) indicated high adaptability and potential for the formation of virulent races. Ecological analysis revealed a low alpha-diversity level (H′ = 1.13–1.32) and a high dominance index (D = 0.42–0.51), indicating structural simplification and increased pathogen specialization. Three functional fungal groups were distinguished – primary pathogens (Fusarium spp.), opportunists (Phoma betae), and necrotrophs (Rhizoctonia, Botrytis) – which form a hierarchical model of the parasitic complex. The results confirm the cumulative effect of short crop rotations and demonstrate the necessity of integrating biocontrol agents (Trichoderma, Gliocladium) and ecological soil sanitation measures to restore microbial balance and reduce infection pressure in short-rotation systems of the Western Forest-Steppe.
Kyselov et al. (Thu,) studied this question.