| Rice blast disease, caused by Magnaporthe oryzae, is one of the most fungal diseases in the rice planting region of the world. This disease not only influences the yield and rice quality but also causes serious economic losses. Currently, Breeding and planting disease-resistant cultivars are still the most effective methods to control this disease. Because of pathogenic differentiation of M. oryzae, resistance of rice cultivars is easily overcome in 3-5 years. Thereofore, genetic diversity in the M. oryzae population was studied to facilitate the rice breeding for durable resistance and the disease integrated management.Four sets of differential varieties were used to identify the rice blast fungus, which isolated from Jiangsu and Liaoning in 2011 and 2012. Based on Chinese race differentials varieties,257 Magnaporthe oryzae strains that isolated from Jiangsu and Liaoning Province in 2011 were identified and categorized into 23 physiological races in 7 groups, in which Jiangsu isolates had 12 physiological races in 5 groups and Liaoning isolates had 21 physiological races in 7 groups. The frequency of dominant races ZG1 and ZC15 were 30.84% and 19.63%in Liaoning population; while it was 52.92% for Jiangsu dominant race ZG1. While 197 Magnaporthe oryzae strains that isolated from Jiangsu and Liaoning Province in 2012 were identified and categorized into 14 physiological races in 6 groups, in which Jiangsu isolates had 6 physiological races in 5 groups and Liaoning isolates had 13 physiological races in 6 groups. The frequency of dominant races ZG1 and ZE3 were 25.89%and 10.15% in Liaoning population; while it was 35.03% for Jiangsu dominant race ZG1. The Tsunematru mono-resistance gene lines from Japan differentiated Jiangsu and Liaoning strains in 2011 into 37,46 races respectively. In Jiangsu population the frequencies of dominant races 011,011.2 and 000 were 25.33%,14.67% and 12.67%, respectively; while it was 28.97% for Liaoning dominant race 011.2. While the Tsunematru mono-resistance gene lines from Japan differentiated Jiangsu and Liaoning strains in 2012 into 24,42 races respectively. In Jiangsu population the frequencies of dominant races 011.2 was 28.57%; while it was 34.34% for Liaoning dominant race 011.2. Based on LTH-NILs Jiangsu and Liaoning strains in 2011 can be categorized into 27 and 23 pathogenic types, respectively. While Jiangsu and Liaoning strains in 2012 can be categorized into 15 and 22 pathogenic types, respectively. Evaluation by Pot2-rep-PCR and setting the similarity at 75%, the genetic diversity of the tested strains in 2011 can be categorized into 13 lineages, among which there were 12 in Jiangsu and 6 in Liaoning. The frequencies of dominant lineages L11, L12 and L4 in Jiangsu were 22.67%,16.67%,17.33%, respectively; while it was 55.14% for Liaoning dominant lineage L12. While the genetic diversity of the tested strains in 2012 can be categorized into 6 lineages, among which there were 5 in Jiangsu and 3 in Liaoning. The frequencies of dominant lineages L5 and L6 in Liaoning were 40.40% and 27.92%, respectively; while it was 92.86% for Jiangsu dominant lineage L6. In comparison to Jiangsu, the virulence of Liaoning strains was higher and the virulence diversity showed the opposite trend to the genetic diversity. Taken together, isolates from Jiangsu and Liaoning were similar in both pathogenicity and genetic structure but were significantly different in heterogeneity.The four rice varieties Aichi Asahi, Kusabue, CO39, Suyunuo, were single planted and two mixing planted and four mixing planted, a total of 11 treatments.15 strains of M. oryzae(5 strains from Jiangsu,5 strains from Liaoning,5 strains from indica region) which were significantly different in the fingerprint were mixed inoculated on those treatments, the results showed that:after the mixed inoculation, different strains were screened on the different types of rice varieties.7 strains (strain number:1,5,7,9,10,14,15) were screened under the Aichi Asahi rice varieties and the highest frequency strains were 7(22%), 9(20%),15(18%).8 strains (strain number:2,3,4,7,9,11,14,15) were screened under the Kusabue rice varieties and the highest frequency strains were 7(30%),3(18%),2(14%). Different mixed combinations have different effects on rice blast fungus population structure, compared with the variety of single rice, it is not the simple addition of single plant cases which has its characteristic each.6 strains (strain number:3,4,5,7,9,13) were screened from the mixed planted rice with Aichi Asahi and Kusabue and the highest frequency strains were 7(30%),9(20%),4 (18%).4 strains (strain number:4,7,10,11) were screened from the mixed planted rice with Aichi Asahi and CO39 and the highest frequency strains were 4(45%),7(35%),10 (18%). While 9 strains (strain number:2,3,4,5, 7,9,10,13,15) were screened from the mixed planted rice with Aichi Asahi and Kusabue and CO39 and Suyunuo and the highest frequency strains were 4(22%),7(20%),13 (14%). Different varieties of the rice have different effects on the blast fungus after 2 generation transgenerational infection. On the Aichi Asahi rice, advantage strains in number 7,9 were more apparent and strain number in 10 was disappeared with the emergence of a new strain type 17. On the Kusabue rice, advantage strain in number 7 was still advantaged, strain number in 4,11 rised to new advantage strains, strain number in 9 disappeared with the emergence of a new strain type 22. Different mixed combinations have different effects on the blast fungus after 2 generation transgenerational infection. On the Aichi Asahi and Kusabue rice, strain number in 7 maintained its advantage while strain number in 4 was on the rise with the emergence of new strains type. On the Aichi Asahi and Kusabue and CO39 and Suyunuo mixed planted rice, strain number in 4,7 maintained their advantage. Taken together, the effects on the rice blast fungus which comes from mixed combinations were completely different from the variety of single rice. The mixed combinations produced a new selection pressure, mixed combinations and single planted rice were also completely different on the continuous screening of rice blast fungus. |
