Abstract only

Scientific literature provides the data sug- gecting that increased radiation can considerably change the level oí virulence oí phytopathogenic organisms and consequently alter the host range of pathogens. Thus, we focused at investigation of the influence of gamma-radiation on pathogenicity of wheat rust. Inoculum propagules of brown rust (Puccinia recondita) and stem rust (Puccinia graminis) were used for the experiment. Their uredospores were irradiated with gamma-radiation at the different rates of 500to 3500 grey. The effect of irradiation on pathogenicity of the parasites was assessed based on the appearance and intensity of growth of hyphas of uredospores as well as bythe artificial inoculation of tetraploid (Dika 9-14, Shavpha) and hexaploid (Bezostaya 1, Doli 35-4, Mostinave) varieties of wheat at the stage of 3-4leaves. The results were observed on the second and the tenth days of irradiation. It has been observed that on the second day Of irradiation the same radiation rate has the similar effect on the both types of rust. The dose of 500 grey does not cause considerable changes in growth of uredospores. Namely, germination of spores of brown rust increased by 2-3% and of stem rust only by 0.5% as compared to unirradiated check. Stimulation effect was observed at 1000 grey. The spores of both brown and stem rusts germinated more intensively then in case of the check, showing increase by 9.3% and 7.7% respectively. At 1500 grey and above rates the growth of the spores gradually declined. At 3500 grey it decreased in brown rust by 7,4% and in stem rust by 12,9%. On the tenth day of irradiation the major part of the spores of both species have lost vitality. Pathogenicity and germination of the survived spores was the same as on the second day of irradiation proportionally to the radiation rates. Inf1uence of irradiation on pathogenicity of the spores of wheat rust was investigated also using the artificial inoculation of plants. The spores irradiated by the 500 and 1000 grey doses proved to be more infectious than the unirradiated ones. Pathogenic effect decreased at the rate of 1500 grey. This dose proved to be semilethal for parasites. The spores irradiated by the 2000 grey dose fail to infect tetraploid varieties, while for hexaploid varieties very low infection intensity was recorded. The parasites maintained certain level of pathogenicity even after ten days from irradiation proportionally to the radiation rates. Based on the test results we arrived at the conclusion that irradiation resistance of the wheat stem rust pathogen is higher than that of the brown rust pathogen. At the same time the certain rates of irradiation considerably increase the level of pat- hogenicity.

English

0409|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

CIMMYT Publications Collection