The conidia Bipolaris sorokiniana Sacc. Shoem. distribution in the soil of Altai and Kazakhstan arid regions

The purpose of the study was to assess the number and state of populations of B. sorokiniana conidia in the soil of agrocenoses and virgin areas. Studies were carried out in 2017-2021 in dry steppe regions of the Altai Territory (Russia) and Pavlodar Region (Kazakhstan) by conventional methods. For the experimental data analysis variance and correlation analytical methods were used. A comparative analysis of Bipolaris sorokiniana conidia populations in agrocenoses and virgin soils of arid areas was carried out. A significant phytopathogen conidia population in agrocenosis soils has been established, reaching 10.8 regional economic harmfulness thresholds in Altai and 16.6 thresholds in Kazakhstan. A lower population number in virgin soils was revealed in comparison with agrocenoses’ ones, which is associated with more active resting structures degradation. A clear tendency towards a decrease in the number of conidia with increasing depth was revealed, which manifests itself to different degrees in the regions and tillage systems, but has the same orientation: the upper layer (0-5 cm) is populated several times stronger than the lower (10-15 cm) one. The phytosanitary precursors in both regions (fallow, sunflower, pees, oat with vetch, sweet clover) reduced the conidia number in the soil on average 59%; they significantly increased the conidia proportion with the degradation signs-average by 27.1%. Soil suppressive activity against B. sorokiniana increased significantly (on 19.8-38.3%) after cultivation of phytosanitary predecessors, especially rape.