To artificial inoculation of sunflower plants with modern pathotypes of rust for breeding on immunity

Under global warming of the last decade, there is observed an intensive spread of rust in sunflower fields in the Russian Federation, due to the emergence of new races of the pathogen. It is obvious that there is a need to breed sunflower for resistance to new pathotypes and to correct the technique of artificial inoculation of plants in relation to them. Sunflower breeding for rust resistance has not been carried out since the 1980s. Objective of the study is determining the optimal temperature range for artificial inoculation of sunflower leaves with modern pathotypes (300 and 700) of the rust pathogen. The work was performed in the laboratory of immunity of the V.S. Pustovoit All-Russian Research Institute of Oil Crops in 2020–2021 using monopustular isolates of Puccinia helianthi with virulence codes 300 and 700. The germination of mature urediniospores, the duration of the incubation period and the degree of damage to sunflower plants at different temperatures were studied. The incubation period of pathotypes 300 and 700 of P. helianthi at a temperature of 26–28 °C is reduced by 2–3 days, which is essential both for the rapid identification of the racial identity of the pathogen isolates and for shortening the period for assessing sunflower genotypes when breeding for immunity. To speed up this work, the infection of sunflower plants should be carried out in the phase of the first pair of true leaves at a temperature of 22 °C, followed by a 24-hour stay in a humid chamber at 20 °C and a further increase in the growing temperature to 26–28 °C.