Study On Steady Differential Fungus Strains Of Rice Blast In Sichuan

The rice blast caused by Magnaporthe grisea was one of the epipHyte disease of the most prevailed-wide and big-damaged. Now the best ways of economical and efficient to prevent rice blast is to make use of resisted breeds and make them distribution with reason. When these breeds were been put into use in 3～5years or less time, the fastness of breeds will lose. The reason is that rice blast pathogenicity and special fastness of rice breeds have changed. This passage is about studying on steady differential fungus strains of rice blast in Sichuan. The results are as followes:1. The 105 isolates collected from rice in Sichuan were studied with three sets of differentials. The Chinese race differentials, the CO39 near isogenic lines, the Tsunematru mono-resistance gene lines from Japan could differentiate 105 isolates into 7,19 and 103 pathogenic types respectively. The Tsunematru mono-resistance gene lines from Japan had a evident differentiating ability. Cluster analysis showed that compared with Chinese race differentials, there was no distinctive correlation with pathogenic types.2. From the 105 isolates, we choosed 20 isolates that had good conidia and strong pathog enic ability. With the Chinese race differentials, lots of the population of cultivating subcultu re M.grisea did not change, but the race of M.grisea isolates to some extent had transformed during cultivating subculture M.grisea isolates. The strong pathogenic ability was instability. Virulence of M.grisea gradually died away in the course of cultivating subculture M.grisea isolates. The pathogenic types of most subculture M.griseaisolates of strains had evidently changed on the Tsunematru mono-resistance gene lines from Japan, whose innocuous genes comed forth obviously change. The genes between innocuity and virulence could transforme each other. The innocuous genes of few subculture M.grisea isolates of strains did not vary. So with cultivating subculture, the innocuous genes of most isolates had chaged in different degree.3. After pathogenicity detection, we chosed 10 strains whose pathogenicity was relatively steady to detect biological characteristic and molecule detection. In different temperature, the average speed of mycelial growth of subculture M.grisea did not happen clear change. With cultivatin g subculture, the ability of producing conidia becomed to weaken; In different pH, the average speed of mycelial growth of subculture M.grisea also did not happen clear change, but the growth had imperfect current. The number of conidia happened distinctly transformation and the number of conidia of the later was less than the front; The average speed of mycelial growth of subculture M.grisea was not obviously effected by different illumination and the number of conidia had great change. At molecule detection, the isolates could be divided into different genetic lineages in different resemble lev el. During cultivating subculture, the genetic diversity between subculture M.grisea had little diff erence. With the pathogenicity weakening, the variance of isolates becomed steady; Few strains happend biggish variance, there was no distinctive correlation betwwen pathogenic types and genetic lineages.