Host resistance responses against Puccinia striiformis f. sp. tritici in wheat cultivars with different resistance levels: molecular, biochemical, and ultrastructural studies

BackgroundYellow (stripe) rust of wheat, caused by Puccinia striiformis, is a serious disease that results in great economic losses. This study aimed to investigate the variation in plant responses in three wheat cultivars with different resistance levels against yellow rust.ResultsThe highest disease severity was recorded for cv. Gemmieza-11 (95%), followed by cv. Shandweel 1 (60%), while the lowest was recorded for cv. Misr-3 (3%). qPCR results of the yellow rust-resistance genes Yr5, Yr10, Yr15, and Yr18 showed that the infection did not affect the expression of Yr5 and Yr15 in the infected Gemmieza-11 plants when compared to the non-infected control. In contrast, the infection significantly overexpressed Yr5 and Yr15 in cvs. Shandweel 1 and Misr-3. However, Misr-3 was superior in this regard, recording 3.85- and 4.07-fold for Yr5 and Yr15, respectively. In addition, the infection significantly upregulated Yr10 and Yr18 in the three tested cultivars, with the superiority for the cultivar Misr-3, followed by Shandweel 1. Activity of the antioxidant enzymes peroxidase, polyphenol oxidase, and catalase was significantly higher in the infected plants of cv. Misr-3 than in cv. Shandweel-1, while the lowest values were recorded in cv. Gemmieza-11. The increment in this activity was associated with a reduction in the lipid peroxidation in the three tested cultivars. The phenolic content considerably increased also upon infection in cv. Misr-3 followed by Shandweel-1 but not in cv. Gemmieza-11, compared to the non-infected plants. Transmission electron microscopy demonstrated that the infected mesophyll cells in cv. Gemmieza-11 showed abnormalities in the chloroplasts and thick-walled haustoria. On the contrary, the mesophyll cells in cv. Misr-3 showed no haustoria and well organized chloroplasts. The mesophyll cells in cv. Shandweel-1 displayed highly degenerated haustoria, a degenerated granulated cytoplasm, and a thick host cell wall, indicating intermediate defense responses against the invading pathogen. Plant growth, yield, and photosynthetic pigments were higher in cv. Misr-3, followed by cv. Shandweel-1, and the lowest values were recorded in cv. Gemmieza-11.ConclusionsThe obtained results displayed that Yr5 and Yr15 were more effective than Yr10 and Yr18, indicating their main roles in regulating multiple defense mechanisms and hypersensitive responses.