Studies On The Dormancy Characteristic Of Rice False Smut Ball And Chlamydospores Of Ustilaginoidea Virens

Rice false smut is a fungal disease caused by Ustilaginoidea virens (Cke)Tak, which harmed the panicles of rice. Rice false smut is a worldwide disease, and became more and more seriously in recently years, which not only influence greatly on the yield and quality of rice, but ustiloxins also cause poisoning to human and animals.This study observed the structure of different color rice false smut ball by using paraffin section, and found that the rice false smut balls was divided into three layers: Chlamydospore mound;endosperm layer; subiculum, and there was no crossed interface between the subiculum and endosperm layer. In yellow rice false smut balls, an anther with complete pollen sac and pollen grain; in black one there was only part of the outer wall of anther (mainly contained cellulose and lignin), other parts has been infected. The surface and internal structural differences of yellow and black dormant chlamydospores of Ustilaginoidea virens on mid-and late-season rice were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM revealed that the spherical yellow and black chlamydospores had prominent spines, with diameters from 3 to 6μrn and 4 to 6μm, respectively. The spines were 200-700 nm and 400-1100 nm long in yellow and black chlamydospores, respectively. TEM revealed that the cell wall of both color chlamydospores were composed of two layers, the thick endosporium and thin exosporium, and the thickness of the former layer of the black chlamydospores was nearly two times more than that of the yellow ones. The organelles in yellow chlamydospores such as the nucleus were obviously visible, but invisible in black chlamydospores. The cytoplasm of black chlamydospores was occupied by a big lipid globule.To explore the optimum method to wall-breaking of chlamydospores of the rice false smut fungus, Four wall-breaking methods and two enzymes (lysozyme and snailase) were been used. Results showed that Liquid nitrogen grinding plus ultrasonic crushing technique was the best one, its wall-breaking rates on yellow and black chlamydospores could all reached over 98%, and the soluble protein content also achieved the highest values. Therefore, liquid nitrogen grinding plus ultrasonic crushing method is an effective, economic, convenient wall-breaking method for U. virens in the laboratory.Alkali extract was used to extract the cell wall protein and polysaccharides, and studied with Coomassie Brilliant Blue(CBB G-250)method and the method of anthrone, respectively. Result revealed that the cell wall of yellow chlamydospores with protein 9.698% and polysaccharide 73.867%, and cell wall of black chlamydospores with protein 14.187% and polysaccharide 81.207%.