Phytopathogenic micromycetes of spring wheat root rot in crop rotations at different fertilization levels

The aim of the study is to assess the occurrence of phytopathogenic micromycetes - causative agents of root rot of spring wheat in the forest-steppe zone of the Irkutsk Region. Experimental design: predecessors - fallow in crop rotation fallow - wheat - oats, pea-oat mixture and corn in the crop rotation pea-oat mixture - wheat - corn - wheat; soil cultivation methods - plowing with a PLN-5-35 plow to a depth of 20-22 cm, disking BDT-3 to a depth of 12-14 cm; fertilization - no fertilizers, complete mineral fertilizer N45P45K45. Fungi from the genera Fusarium, Alternaria dominated on the seeds, and Bipolaris (Helminthosporium Link) was less common. Seed infestation was 2.9-6.7 times higher than the economic threshold of harmfulness. Fungi of the genus Fusarium were predominantly present in the seeds, rhizosphere, roots and basal part of the stem of spring wheat seedlings. Micromycetes of the genus Fusarium in the rhizosphere of wheat seedlings when sown after fallow and maize compared to the pea-oat mixture decreased by 8.1 and 12.8 %, respectively; by 5.9 % when plowing compared to disking; by 2.3 % when fertilized compared to the unfertilized background. Bipolaris sp. was absent in the soil of the wheat rhizosphere (fallow, N45P45К45), its occurrence decreased by 3.5 times when sown after maize compared to the pea-oat mixture predecessor, which led to lesser infection of the roots and basal part of plants with Bipolaris sp. in these variants. The predecessor corn contributed to the accumulation of Alternaria sp. in the rhizosphere by 6.7 times more than after the pea-oat mixture, and by 19.3 times more than after fallow. Alternaria fungi in the rhizosphere were inhibited by plowing compared to disking by 1.4 times. The fertilized background increased the occurrence of Alternaria sp. by 2.3 times. In comparison with the predecessor corn, after the pea-oat mixture, the infection of Alternaria sp. of the root system increased by 8.1 %, and of the basal part of the stem by 8.9 %.