ULTRASTRUCTURE OF STRIPE RUST (PUCCINIA STRIIFORMIS f. sp TRITICI) INTERACTING WITH SLOW-RUSTING, HIGHLY RESISTANT, AND SUSCEPTIBLE WHEAT CULTIVARS

Interactions between slow-rusting, highly resistant and Susceptible cultivars of common wheat (Triticum aestivum) with stripe rust (Puccinia striiforms f. sp. tritict) were studied at the ultrastructural level. The rust fungus extensively colonized leaves of the susceptible wheat cv. Mingman 169, but was limited or extremely limited in the leaves of slow-rusting cv. Dongfanghong 3 and of the highly resistant Hybrid 46. Microscopic observations Showed that nearly all haustoria and hyphae were inhibited in the nearly immune cultivar, the majority of them were inhibited in the slow-rusting cultivars but nearly all of them developed normally in the susceptible cultivar. The highly resistant cultivar showed heavily necrotized cells, while in slow-rusting wheat cell necrosis Occurred during the process of hyphal extension. The slow-rusting cultivar has the same hypersensitive response characters as the resistant cultivar, but the host cells necrotized later and were fewer in number. This inhibited only in part the fungal growth, which resulted in lesser inhibition and necrosis of the fungus As in the resistant cultivar, defense structures and materials associated with defense reaction were also produced in slow-rusting wheat, but to a lesser extent. The cytological similarities of slow-rusting With hypersensitive resistance are briefly discussed