Research On Rice Blast Resistance Of Founder Parents Of Early Japonica Rice In Cold Region

The climate of early Japonica rice in cold region is cool, its average temperature is20℃during late July to early August, ten-day sunshine hours are under60h. During this period, therelative humidity is above95%due to the rainfall and easily leading to rice leaf blast. In lateAugust, there is rainfall more than50mm, and the relative humidity is over85%.It isconducive for bacteria to the breeding in this situation, and provides incidence condition forthe later stages of infection. In Heading and flowering stage, the daily mean temperaturecomes to18℃below, causing rice dysplasia, and panicle blast often occurred serious.45early japonica rice standard samples of blast are collected to separate116single spore isolateswhich is used to study the physiological races, disease-resistant identification, distribution ofresistance gene and genetic inheritance in order to solve the above problems and provide atheoretical basis for blast resistance breeding. The main results are as follows:There are7group20different varieties of physiological race obtained by identificationof7group of the national unity.ZA is the dominant microflora, followed by ZD and ZBflora, the frequency of occurrence are47.41%,22.41%,15.52%respectively; ZA49is thepredominance, frequency of occurrence (26.72%), followed by ZD5(10.34%) andZD1(8.62%). Meanwhile, it shows that the physiological races present high disease resistancefrequency to the varieties which carrying the Pi-k, Pi-i, Pi-a gene in frigid area (from65.8%-87.1%). And it also suggests that those varieties which only carrying these gene aresusceptible to the disease. Through the comparative analysis of Early Japonica Rice in coldregion in recent30years of physiological races of evolution, we have found the original weakphysiological race gradually rising to the predominance causing the species are susceptible tothe disease, rather than the emergence of new physiological races led to the loss of resistanceof varieties.According to the resistance identification of bred varieties and backbone parents by7group of20Chinese physiological race in frigid area in2008-2009, Ishikari-shiroge、Shangyu397within8backbone parents are susceptible and others resistant. There is asignificant difference between blast susceptible and resistant among86bred varieties derivedfrom the8backbone parents.76samples present leaf blast resistance,53samples presentpanicle blast resistance. However, poor resistance is reflected in bred varieties derived fromIshikari-shiroge and Shangyu397. Using20physiological races to analysis the backbone ofthe pro-anti-spectra and pedigree, Ishikari-shiroge shows blast susceptible and that of pro-anti-spectra is60%. Hejiang20(Pi-i, Pi-a, Pi-ta) come from20Chinese races showsresistant. WuYou1, the third generation backbone parent derived from Hejiang20(Pi-i, Pi-a,Pi-ta) and SongJing3(Pi-a, Pi-ta), resistant to19Chinese races except ZB25.Rattan138(pro-anti-spectra,10%) is susceptible. Suijing3, the second generation backbone parent ofIshikari-shiroge and Rattan138is susceptible, the remaining19races resistance to ZE1.Kendao10(pro-anti-spectra,20%), the second generation backbone parent originated fromIshikari white-haired and Fushiskari ZA17; ZG1shows sensitivity to rice blast, the remainingshows resistance. The core backbone parent(Ishikari-shiroge) presents blast susceptible.However, its second and third generation parent resistant. There are two possible reasons forthis phenomenon. One is polymerization of multiple resistance genes, the other isintrogression from exogenous resistance genes to the core gene pool.The functional markers Pi-b and Pi-ta which designated from the gene itself are used toidentify Pi-b and Pi-ta for backbone parent and its derivatives in cold region. The resultshows that, Kendao13, Kendao14, Longjing22and Songjing9carry the Pi-b gene,Dongnong428, Longdao5, Longjing18, Longjing28, Suijing4,and Suijing9carry Pi-ta gene.Mixed species inoculation showed that the varieties which carried Pi-b and Pi-ta possess highblast resistance,suggesting that the two genes for resistance have high utilization value forbreeding. By using dominant marker of Pi-ta combined with pedigree analysis, the utilizationof Pi-i gene is accompanied by introduction of the Japanese variety Ishikari-shiroge. The firstbackbone parent Ishikari white (Pi-i) and backbone parent Nonglin11(Pi-ta) hybridsderived from the Hejiang12(Pi-i, Pi-ta), and Hejiang12and backbone parent Xiayi(Pi-a)hybrids derived from new backbone parent Hejiang20(Pi-i, Pi-a, Pi-ta), The high blastresistance of Hejiang20is the result of polymerization of multiple resistance genes（Pi-i、Pi-a、Pi-ta）. The distribution of Pi-ta among derivatives of Hejiang20is identified by usingdominant marker of Pi-ta. The result shows that the frequency of Pi-ta-occurrence in the First,the second, the third generation are63%,33%and9%respectively. The transfer of Pi-taresistance gene and the20derived varieties are consistent. The frequency of Pi-ta geneoccurrence in progeny is positively correlated with derived varieties resistance frequency,which may be associated with resistance gene loss during the offspring selection, is also oneof the main causes of rice blast.