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Changes of epidemiological components and histopathology in infection process of UV-B induced mutant strains of Puccinia striiformis f. sp. tritici

Yaqiong Zhao: Department of Plant Pathology, China Agricultural University

<div>Planting resistant cultivars is one of the key measures to control wheat stripe rust caused by <em>Puccinia striiformis</em> f. sp. <em>tritici </em>(<em>Pst</em>), while their resistances are often lost because of the virulence variation of <em>Pst</em>. In this study, the urediospores of a Chinese major physiological race CYR32 were irradiated under the UV-B intensity of 250 μw/cm<sup>2</sup> (at which the relative lethal rate of urediospores was 90%) to screen virulent mutants on a wheat cultivar Guinong 22 that cannot be infected by CYR32. Radiation times of the UV-B radiation doses (LD<sub>50</sub> and LD<sub>90</sub>) for which the relative lethal rates of urediospores were 50% and 90% under the intensity of 150 μw/cm<sup>2</sup> were determined. The effects of UV-B radiation of LD<sub>50</sub> and LD<sub>90</sub> on the epidemiological components and the changes of histopathology under 1-h UV-B radiation (150 μw/cm<sup>2</sup>) of virulent mutant strains were investigated. Two virulent mutant strains were obtained and named as CYR32-5 and CYR32-61. The radiation times of LD<sub>50</sub> for CYR32, CYR32-5 and CYR32-61 were 90, 180 and 120 min, respectively, and that of LD<sub>90</sub> were 200, 300 and 230 min, respectively. The results showed that the incubation period was prolonged and that the infection efficiency, lesion expansion rate and area under disease progress curve decreased after UV-B radiation. It was demonstrated that UV-B radiation reduced the germination rate of urediospores, the numbers of hyphal branches, haustorial mother cells and haustoria, and the linear lengths of hyphae.</div>