The resistance of more than 700 rice parents to rice sheath blight in different regions of China was identified indoor by the method of inoculation.The indices resistance level and significance were analyzed in the experiments.Disease resistance identification analysis indicated that the disease resistances among the parents were significantly different.700 parents were classified into 4 types:resistance,moderate resistance,moderate susceptibility and susceptibility.25 resistance parents and 21 moderate resistance parents were screened from all the parents in this study.Others were moderate susceptibility and susceptibility parents.Finally,the results would provide reference to select the high resistance to rice sheath blight breeding samples and gene resources.

Fifty-five rice sheath blight samples were collected in rice from five distinctive ecological regions of Sichuan province. The 55 representative samples were isolated and purified,and field pathogenicity identification were analyzed. Pathogenicity identification analysis indicated that the pathogenicity among the strains were significantly different. Different pathogenic fungi and different resistance rice race had the pathogenicity significant different from the 55 counties.The results showed that we would find rice sheath blight and pathogenicity distribution characteristics,in order to control the rice sheath blight epidemic and reduce the infection to rice or maize. Finally, it would provide reference to select the high resistance to rice sheath blight breeding samples and gene resoures.

Fifty-five representative samples of Rhizoctonia solani isolates, which were collected and isolated from five different ecological regions in Sichuan Province, China, were purified and analyzed for the pathogenicity and molecular genetic variation. The hyphal fusion test revealed that almost all the isolates belonged to the AG-IIA group except the isolate D42. In addition, some of the isolates were 'bridging isolates', which could fuse with several groups simultaneously. The pathogenicity analysis on in vitro leaves confirmed a significant pathogenicity variation in the tested isolates. The 55 isolates were then classified into 8 groups by further RAPD (randomly amplified polymorphic DNA) cluster analysis at the similarity coefficient of 0.941. The results suggest that under the certain ecological conditions in Sichuan Province, China, most of the R. solani strains were genetically stable, but a few changed drastically.

A G protein β-subunit gene in Rhizoctonia solani AG-1IA of rice which causes rice sheath blight disease was isolated. A 1958-bp PCR fragment was obtained by using the specific primers designed from the conserved region in G protein β-subunit homologues from Thanatephorus cucumeris. Amino acid sequence analysis showed that the sequence involved 366 deduced amino acid,encoded a putative peptide which shared significant identity (57.34%-88.14%) with G protein β-subunit homologues from other species. The full-length of the PCR fragment was 1.9 kb with a 1.7-kb open reading frame of the G protein β-subunit gene in R.solani AG-1IA. The results of RT-PCR showed that the G protein β-subunit gene transcript was greatly expressed in all growth period especially at the exponential phase,which indicated that the expression of the G protein β-subunit gene in R.solani AG-1IA might be regulated temporally and spatially.

Based upon the genomic sequence difference between the indica rice variety 93-11 and the japonica rice variety Nipponbare,a total of nine molecular markers for starch branching enzyme gene(Sbe)were successfully developed.All the markers were utilized for genotypic screening and further analysis of the correlation between genetic polymorphisms of Sbe1 and Sbe3 genes and the rice starch characteristics.The genetic polymorphism of the markers had no influence on starch physiochemical traits,that is these allelomorphism variation sites of Sbe gene had no influence on the starch traits of non-glutinous rice.There were six markers which could be used to accurately identify indica rice varieties with a reliability over 80%.Meaning of marker development and molecular marker assisted selection were also discussed.