Research On Delaying Of Rice Varieties Resistance To Rice Blast And Evaluation Of Resistance Level

Rice blast, which is caused by fungus of Magnaporthe grisea (Hebert) Barr., was one of main diseases that decrease yield in the world. It is also a problem, in Jilin Province, China. At general year, the affected areas almost were 1 million hectares. So, how to prolong varieties resistance and how to evaluating its resistance to guide product, it plays an important role in practice to control rice blast disease, to give suggestion to early-warning. Under this background, we made this research on prolonging rice varieties resistance to rice blast disease and evaluating the level of rice varieties resistance to rice blast disease. The results are as follows.First, the reasons that rice varieties losing their resistance to rice blast disease were clarified.The main reason was from the pathogenic physiological races(lines) which came from the variation of the rice blast disease and became the pathogenic dominant physiological races in proper surroundings .The second reason was there was less diversity in resistant resources. In Northeast of China, the material of resistance to rice blast was less, some materials with resistance to rice blast were utilized as the parents in some area by different breeder at the same time, then the new varieties which came from the same parents owned the same characteristics of resistance to rice blast, this made them to lost their resistance when some no virulent gene disappear (or absent) in virulent strains easily.The third reason was impractical distribution of varieties in fields that resulted in easily losing its resistance. During the course of varieties extending, their distribution were short of united control, then pathogenic physiologic races appeared directly in special environment, and this resulted in varieties losing their resistance to rice blast quickly.The fourth reason was impractical method of planting that decrease a variety resistance. And it mainly embodied on not properly on amount and period of the nitrogenous fertilizer application, and that resulted in plant losing its natural physiological function and decreased resistance.Unfavorable conditions of climate were the objective factors that resulted in rice cultivars losing resistance, and made the rice blast to prevail.Second, based on the characteristics of the North China, four measures to prolonging resistance of rice varieties to rice blast disease were concluded. They were as follows.Based on characteristics of varieties to fertilize nitrogenous fertilizer, through suitable amount applied, rice varieties resistance would be enhanced. Based on the relationship between the potential yield, sensitive degree to nitrogenous fertilizer and degree of susceptible to the rice blast disease, to decide the amount applied was an ideal measure to prolong resistance to rice blast.By planting different varieties, to prolong rice varieties resistance to blast. By using theefficiency of biological diversity to select the varieties with resistance to different races of Pyriculary oryzae, the results indicated it can restrain the directional evolution to some single race, and avoid the dominant races coming into being, thereby it prolonged the resistance to rice blast disease.By understand pathogenicity of the dominant races to some varieties in some areas, the suitable varieties would be plant to prolong the resistance to the rice blast disease.Combined with the monitor of physiological races, the relationship between races and families was researched by RAPD technology, the result was guidance to rice product. Third, by analyzing the main factors that cause the disease, simulated the details, and combined with test in greenhouse, a model to foresee a varieties' resistance was set up.Combined with theory of plant epidemic, the formula of evaluating a variety resistant to rice blast level was constructed, which was based on the ratio of pathogenic strains infected and the compared infected ratio of spores and compared producing spores' quantity, the formula was: CISI (Compared Integrated Susceptibility Index) = 1000xISIr/ISIck, ISI (Integrated Susceptibility Index) = the ratio of pathogenic strains infected * the compared infected ratio of spores x the compared producing spores' quantityx amended coefficient the compared producing spores' quantity.As the pathogenic ratio of strains was varieties' vertical resistance, compared infected ratio and compared producing spores quantity embody varieties' horizontal resistance, so CISI (ISIr/ISIck) was a variety's compared integrated susceptibility level. So if a variety CISI value is smaller, then it has lower susceptible level, and has higher resistance level. On the contrary, if a variety CISI value is bigger, then its resistance is poorer, and it is more susceptible. And veracity of the formula was testified in practice.