Physiology Mechanism And The Ultrastructure Studies On The Resistance To Sunflower Rust

Sunflower rust, which is one of the major diseases of sunflower, globally spreads in the sunflower planting area triggering a heavy loss in the production. In this study, in order to reveal the mechanism of host resistance, leaf structure, changes of defense enzymes, several resistant material and accumulation of reactive oxygen species on resistant and susceptible cultivars were detected. Also, the infection process of Puccinia helianthi Schw. by electron microscope was observed. Results were as follows:1. The dynamic changes of defensive enzymes and several resistant materials on sunflower infected Puccinia helianthi Schw. with different compatibilities were studied. The results indicated that PAL, PPO, POD, SOD, CAT, the contents of host soluble sugar, soluble protein, chlorophyll-a, chlorophyll-b and carotenoids changed after infected by the rust. All these physiological indexes except the contents of host soluble sugar and chlorophyll-a had close relationship with host resistance, and could be served as criteria for assessing the resistance of sunflower to Puccinia helianthi Schw.2. Study of the relationship between sunflower rust and the production and accumulation of reactive oxygen in the interaction of rust fungus of sunflower with different resistance showed that the accumulation of H₂O₂ and O₂^-·had a significant positive correlation with plant's resistant performance. In addition, the reaction time of hypersensitive reaction of cell necrosis was later than the initial production time of H₂O₂ and O₂^-·. This showed that the production and accumulation of H₂O₂ and O₂^-·did a great deal with cell necrosis allergies of the host.3. Leaves structure between resistant and susceptible cultivars were different, research on leaves structure included thickness of leaves, number of palisade tissue, thickness of the first line palisade cell, the second line palisade cell, upper epidermal cell and of lower epidermal cell, content of wax and the comparison of stomata density. The result showed that content of wax of resistant varieties leaves was higher than that of the susceptible one,and the palisade tissue arranged closely and in good order, such structure was a good barrier to resist the penetration and extention of hyphae of Puccinia helianthi Schw.. The stomata density was not correlated with the resistance to Puccinia helianthi Schw.4. The observation by electron microscope revealed a significant difference in the fungal development and the host responses between susceptible and resistant sunflower cultivars following infection by the pathogen. Pathogen hyphae grew in the intercellular space between cells or along the cell wall in the susceptible sunflower cultivars. At the early and middle stage of infection process, the host cell became plasmolyzed. The chloroplast was malformed. The thylakoid inside chloroplast became disordered. At the later stage, some chloroplasts collapsed. The main histological manifestation of the pathogen development in the resistant sunflower cultivars includes inhibition of hyphal growth,with no haustorium produced. Host cells'necrosis was closely related with the inhibition of hyphal development. Hypersensitive response (HR) was the main resistance mechanism to this pathogen.