| Abstract: | The incompatible combinations between races of Puccinia striiformis and wheat cuitivars withlow reaction type resistance were examined by means of fluorescent microscopy, differential interference con-trast microscopy and electron microscopy. The incompatible combinations consisted of wheat cultivar Niuzhuteplus CY28, Hybrid46 plus CY29 and Tianxuan882 plus CY29, while the compatible combination was wheatcultivar Huixianhong plus CY28. The observation revealed a striking difference in the fungal development andthe host responses between susceptible and resistant wheat cuitivars following infection by the pathogen. Themain histological manifestation of the pathogen development in the resistant wheat cultivars include inhibitionof hyphal growth, delay of hyphal branching and colony formation, decrease of formation of haustorial mothercells and haustoria, and occurrence of host cell necrosis. The observation by electron microscopy demonstratedthat a series of abnormal changes occurred in intercellular hyphae, haustorial mother cells and haustoria dur-ing pathogen development in the resistant wheat cultivars. The cytoplasm became more electron-dense and vac-uoles in the cytoplasm increased in number and size. The cell walls of hyphae, haustorial mother cells werethickened irregularly. The organeiles were disorderly distributed in the cytoplasm and the haustorial mothercells and haustoria lost their physiological function. In the final stage of the pathogen development, the inter-cellular hyphae, haustorial mother cells and haustoria became necrotic and collapsed. The structural defensereactions such as formation of cell wall apposition, collar and encasement of haustorium were essentially morepronounced in the infected wheat leaves of the resistant cultivars than in the susceptible one. In addition, therelationship between the host resistance expression and the histological and cytological features occurred in theincompatible combination was discussed in this paper. |
