Study On The Control Effects Of Rice Mixture On Rice Blast And Population Structure

Rice blast, caused by Magnaporthe grisea (Hebert) Barr., is the most devastating fungal disease in the world, and has important effect on the yields. It's a hotspot and focus to using rice mixture to control the rice blast, and it was generalized and application all the country. An epidemic of rice blast occurred in Sichuan province in 2005, and the rice mixture didn't control it effectively. In order to find out the effect of rice mixture on rice blast, we studied on the effects of rice mixture on rice blast, and the difference of race composition and genetic structure of Magnaporthe grisea in rice mixture fields and pure-cropping field. The experimentation was carried out in Xuyong, Zizhong, Yinshan, Pujiang, and Yaan County; the main results of this study are as follows.1. The effects of rice mixture on rice blast were different in different ecological zones. There was no significant difference between rice mixture and monoculture in disease severity of rice blast in severe occurrence region, its disease incidence was 86.46% and disease index was 53.61 in Xuyong County. In Yinshan County, its disease incidence was 6.90% and disease index was 1.08, the disease severities of glutinous rice in many of inter-cropping treatments were highly significant lower than pure-cropping treatment. The control effect of rice mixture on leaf blast of glutinous rice was 12% to 26%, and 0% on panicle blast in Xuyong County. The control effect was 46% to 88% on leaf blast and 11% to 76% on panicle blast in Yaan and Yinshan County. In a word, the control effect of rice mixture on rice blast of glutinous rice was higher in lower disease severity plasce.2. The effects of rice mixture planted with different resistance Hybrid varieties on rice blast were different. The higher resistance the main variety has the higher effect of rice mixture has on rice blast of glutinous rice. When the main variety infected seriously rice blast, there is no significant difference in disease severity between glutinous rices in mixture and monoculture fields.3. The effects of rice mixture planted with different modes on rice blast were different. The effective modes of rice mixture were "4+1" and "6+1", and "1+1" mode can not contol rice blast. The effects of "1+1" mode on rice blast was significant lower than "4+1" and "6+1" modes. When the main variety was susceptible, the effects of all the modes on rice blast were low.4. The virulence of these isolates from pure-cropping and inter-cropping fields was assayed with a standard set of 7 differential rice varieties commonly used in China, the results showed that there was no significant difference of M. gresea race composition between rice mixture and monoculture. The dominant groups both were ZB and ZG group. The proportion of ZB group in mixture fields is about 45%, corresponded with ones in monoculture fields. The types of ZB group was abundant than the others, and a majority of races types in mixture fields were the same as ones in monoculture fields. The avirulence gene of these isolates from pure-cropping and inter-cropping fields was assayed with Tsunematru mono-resistance-gene lines from Japan, the results showed that the type of avirulence gene were the same, and there was no significant difference of frequency between mixture and monoculture. The cross infection of M. gresea from pure-cropping and inter-cropping fields was assayed with 9 commonly planted in Sichuan, the results showed that there was cross infection between isolates of M. grisea in mixture and monoculture, the frequencies of cross infection isolates were 70% to 90%.5. The genetic dicersity of M. grisea from pure-cropping and inter-cropping fields was assayed with 6 pair of SSR primers; the results showed that there was no significant difference of genetic structure between mixture and monoculture. And the genetic lineages of M. grisea in pure-cropping hybrid varieties were abundant than ones in pure-cropping glutinous variety. There was no significant difference of genetic structure between pure-cropping hybrid varieties and inter-cropping hybrid varieties. The genetic lineages of M. grisea in inter-cropping glutinous variey were abundant than ones in pure-cropping glutinous variety, but the dominant lineage both were lineageâ…¦. There was dominant lineage both in mixture fields and monoculture fields, the frequency of dominant lineage were 30% to 80%, and the frequencies of dominant lineage in mixture fields were lower than ones in monoculture fields.