Effect of Chronic Irradiation on Plant Resistance to Biotic Stress in 30-km Chernobyl Nuclear Power Plant Exclusion Zone

It was established in greenhouse experiments that infection with powdery moldew (Erysiphe graminis DC. f. sp. tritici Em. Marchal) and brown rust (Puccinia triticana Erikss. & Henn.) of three wheat (Triticum aestivum L.) cultivars (Mironovskaya 808, Polesskay 70, and Kiyanka) grown from seeds, collected in the Chernobyl exclusion zone, was 1.5-2.0 times higher than of plants grown from control seeds. On field trials in the Chernobyl zone, wheat plant resistance to biotic stress was reduced. At artificial infection with brown rust, the disease development was enhanced on plots with increased radiation background. One of the mechanisms of the declined phytoimmunity potential under the action of low doses of chronic irradiation is evidently a reduced activity of plant proteinase inhibitors. Thus, in wheat and rye (Secale cereale L., cv. Saratovskaya) grains, their activity reduced by 35-60% as compared to control. Active form and race formation in the population of the cereal stem rust causal agent (Puccinia graminis Pers.) was observed in the Chernobyl zone. A "new" population of this fungus with high frequency of more virulent clones than in other Ukraine regions was distinguished. The results obtained independently in greenhouse and field trials performed in the Chernobyl zone demonstrated radiation stress influence on the pathogen-plant interactions. They indicate a necessity of monitoring the microevolutionary processes occurring in both plants and their pathogens under conditions of technogenic stresses.