ULTRASTRUCTURAL ANALYSIS OF THE INTERACTION BETWEEN PUCCINIA STRIIFORMIS F.SP. TRITICI AND WHEAT AFTER THERMAL INDUCTION OF RESISTANCE

Abstract

SUMMARY Wheat cultivars with high-temperature resistance shortly exposed to 21°C expressed resistance to stripe rust, Puccinia striiformis f.sp. tritici, after being inoculated with the virulent strain CY29. Observations on the ultrastructural interactions between wheat and the rust fungus demonstrated that marked changes took place in both the fungus and the host mesophyll cells in resistance expression. Hyphae of the fungus were inhibited, and organelles developed vacuoles and disintegrated or collapsed. Development of haustorial mother cells and haustoria was retarded, and these were malformed and necrotized. The extrahaustorial membrane was stained more deeply, wrinkled, and perforated. The extrahaustorial matrix was widened and was coated with large amounts of electron-dense material. Host cells produced defense structures and material related to infection as well as hypersensitive responses. Formation of cell wall appositions, collars or papillae, and encasements of haustoria were essentially observed. In the interaction of the same wheat cultivars with the stripe rust avirulent strain (CY29-mut3) at normal temperature (16°C), the intracellular symptoms of incompatibility were similar to those of thermal induction. In the compatible interaction at 16°C, the pathogen was normal and there were no signs of disorganization or necrosis of infected host cells.