Influence of climatic conditions on infection of sunflower lines by phoma black stem

The purpose of the research was to analyze three year observations (2018–2020) for the climate changes effect on infection of the breeding sunflower lines (Helianthus annuus L.) by a Phoma black stem pathogen Plenodomus lindquistii (Frezzi) Gruyter, Aveskamp & Verkley in the central zone of the Krasnodar region. The disease was monitored on fields of V.S. Pustovoit All-Russian Research Institute of Oil Crops, Krasnodar. Analysis of climatic factors in years of the research resulted that heavy rainfalls (119.2?134.6 mm) exceeding multi-year averages (60.0 mm) by two times and the optimal average daily temperature 23.0?26.4 ?С in July are favorable for stem infection by Plenodomus lindquistii in the second half of the summer, in a phase of sunflower flowering – maturing. In 2018, the moisture deficit in June (11.0 mm) and August (6.8 mm) was a factor suppressing the viability of an infectious matter of a fungus that led to a low frequency of Phoma black stem on the sunflower lines (in average 20.3%). In 2019 and 2020, prevalence (P) and development (R) of Phoma black stem in average on sunflower lines were equal 23.3?29.9% and 21.4?28.1%, respectively. A line L 107 demonstrated a stable resistance to Plenodomus lindquistii infection during three years: amount of infected plants was within 5.7?8.3%, development was 3.8?8.3% at the infection level of 1–2 points. A susceptible line L 116 was selected (P: 47.5?62.8%, and R: 38.0?40.0%). Among the studied breeding lines, the sample VK 900 was the most susceptible to weather conditions of the year: prevalence of the Phoma black stem varied within 21.1?45.5% at the infection level of 1?3 points.