Septoria blotch epidemic process on spring wheat varieties

The Septoria blotch of spring wheat leaves and ears is one of the most economically significant infections in the Siberian region. In the control systems of Septoria blotch the main ecologically safe element is resistant varieties, which are designed to slow down the pathogens reproduction rate and slow down or stop the development of the epiphytotic process. The purpose of the work was to clarify the species composition of Septoria blotch pathogens for West Siberian regions and spring wheat varieties, to study the epiphytotic process of Septoria differentially on the leaves and ears of varieties, and to evaluate the activity of seed transmission of Parastagonospora nodorum. Studies were carried out in 2016-2018 according to generally accepted methods. Septoria leaf and ear blotch of spring wheat is widespread in West Siberia and the Trans-Urals, causing a decrease in yield by up to 50 % or more with the deterioration in grain quality. The causative agents of the disease are P. nodorum, Septoria tritici, and P. avenae f. sp. triticae, and the species ratio varied across the regions and varieties, and within plant organs. In Novosibirsk Region, P. nodorum completely dominated; S. tritici was 13.8 times less common; and P. avenae f. sp. triticae was a singleton. In Tyumen Region, the dominance of P. nodorum was disrupted in some geographic locations by S. tritici and P. avenae f. sp. triticae. In Altai Krai, P. nodorum predominated at all points studied; S. tritici and P. avenae f. sp. triticae were found everywhere, but 5.6 and 8.6 times less often, respectively. The study of spring wheat varieties of different origins has not revealed any samples immune to Septoria blotch. A differentiated manifestation of resistance to Septoria leaf and ear disease has been established. Some varieties show complex resistance, combining reduced susceptibility to Septoria leaf and ear disease. Seed infection with P. nodorum in the regions of Siberia reached 7 thresholds and was largely (52.5 %) determined by the August weather conditions. The study of the collection of spring wheat varieties from three Siberian regions has revealed the following trend. Transmission of P. nodorum with the seeds of varieties was the most active (7.6 %) in Novosibirsk Region and somewhat weaker in Omsk Region (5.7 %). The most favorable phytosanitary situation was in Kurgan Region, where varieties transmitted P. nodorum to a low degree (2.1 %), below the threshold.