Screening, Evaluation And Utilization Of Rice Germplasm Resources Resistant To Rice Blast (Magnaporthe Grisea)

Rice blast, caused by Magnaporthe grisea (Hebert) Barr, is one of the most devastating plant diseases, infecting rice crops all over the world. It has been proved that breeding and planting disease-resistant cultivars is the most economical and efficient means to control this disease. The pathogenicity variation of rice blast fungus often lead to the loss of resistance in rice plants to different races. Consequently, comprehensive understanding of the composition, distribution and variation tendency of blast fungus races, as well as the resistance variations in main rice cultivars, plays an important role in making breeding strategy for resistance and in arranging appropriately resistant rice cultivars in order to predict and prevent the advent of rice blast disease. Screening and utilization of rice blast resistant germplasm resources is the foundational measure to breed resistant varieties. This study focuses on rice growing area in Sichuan Province, thoroughly analyzing the composition, distribution and variation tendency of blast fungus races, and the resistance variations in main hybrid rice varieties, and systematically investigating, for some of the resistant germplasm resources, the phenotype of blast resistance, main agronomic traits, grain quality, restoring or maintaining characteristics and genetic diversity. Moreover, in order to improve agronomic traits of the resistant germplasm and to produce breakthrough hybrid rice varieties with high-yield, high quality, and comprehensive resistance to blast fungus, the cyto-engineering approaches and conventional hybrid rice breeding techniques, combined resistance identification at early generation with assessment of restoring and combining abilities at advanced generation, have been employed. The main results of this study are as follows:1. From 2002 to 2005, 477 isolates of rice blast fungus collected from Sichuan Province were tested using 7 standard assessing lines. The results showed that the pathogen in Sichuan were composed of 7 groups containing 33 races, in which ZB and ZA group were predominant with a frequency of 74.0% and 19.7% respectively. ZB₁₃ was the predominant race with a frequency of 36.5% and other main races were ZA₁₃ (9.6%), ZB₁₅ (8.2%), ZB₂₉ (7.6%), ZB₃₁ (5.7%) and ZB₅ (5.2%). The composition of pathogen races varies annually and the frequency of ZA group rose from 8.3%-3.4% in 2002 and 2003 to 30.3%-36.7% in 2004 and 2005, reaching the summit. Significantly, the pathogenicity of ZA group is more severe than ZB and ZC, so we have to pay more attention to this trend and make strategies aiming at ZA group. The composition of blast fungus races varies among different ecological regions such as Yaan, Xuyong and Pujiang disease nurseries; as a result it is necessary to assess the resistance in different ecological...