| Rice blast disease is one of the most devasting deseases worldwide.Sichuan is the main planting area of hsien rice and blast disease occurred every year. Since the popularization of hybrid rice in China, the loss caused by Magnaporthe oryzae had been aggravated on a unprecedented large scale due to the breakdown of the single genotype of resistance in the varieties. The genotype and spectra to blast disease in NeiHui 99-14 and 134 commercial rice varieties, of which the majority were hybrid rice, were postulated and tested by inoculating 21 differentiated isolates of M. oryzae of different spectra to 24 lines of which each had a single, different, known resistance gene. Combined with field test, the field resistance to blast of those 134 varieties,25 near isogenetic lines (NILs) of rice varieties which contained single, different resistance genes were identified in year 2008 at Pujiang, Xuyong and Ya'an; also rice hybrid combinations whose father was NeiHui99-14 were identified in year 2009 and 2010 at Pujiang, Xuyong,Yanting and Yingshan. Genetic analysis of NeiHui 99-14 to blast disease were carried out by inoculating 04-6-8-2 and other 359 isolates isolated from different samples which were collected from year 2007 to 2009 in Sichuan province. The results were as follows:1. Most of 25 NILs were susceptible to leaf blast in blast disease nurseries located at Pujiang, Ya'an and Jiangyou in Sichuan Province. The lines which contained Pi-km, Pi-kp, Pi-kh, Pi-z5 and Pi-9(t) were resistant or less susceptible to leaf blast than other lines, separately. Those contained Pi-km and Pi-kh were resistant in all nurseries.2. Only 2 out of the tested hybrid rice, Lu You No.1 and Hong You 44 showed the same compatible spectra to the 21 differentiating isolates. The cluster analysis of the compatible spectra of the tested varieties had classified them into 7 groups when the similarity index computed by DPS software was at 0.80. The genotypes of 2 hybrid rice, D Xiang 287 and Q You NO.2 could be clearly postulated. The former probably contained Pi-km, Pi-zt and Pi-7 and the later were considered to contain Pi-k, Pi-i, Pi-t and Pi-19. Unknown resistant genes were found to be present in other tested varieties.■ 3. D You 202 was moderately resistant to leaf and panicle blast disease at Xuyong, Pujiang and Ya'an. D Xiang 287 were found to be resistant or moderately resistant to leaf blast at Xuyong and Ya'an, resistant to panicle disease at Xuyong and Pujiang, whereas Q You NO.2 were susceptible to leaf and panicle blast at all locations, suggesting the accordance to results to the NILs of the same known genes. The differences in rate of panicle blast were significant between cultivars and nurseries and the interaction between of the cultivars and nurseries were also remarkable.98.48% of the 134 tested varieties were susceptible to leaf blast at Xuyong and Pujiang, while that rate was 63.43% at Ya'an.4 out of 126 varieties were resistant to panicle blast in at least one nurseries,27 varieties were highly susceptible to panicle blast in all nurseries, and other varieties were susceptible or moderately susceptible to panicle blast in all nurseries.4. The negative correlation between resistance frequency and average panicle blast rate, as well as leaf blast grade were significant at 0.01 level (two-tail), and the coefficient were-0.257 and -0.403, separately; the positive correlation between panicle blast rate and leaf blast grade were also significant at 0.01 level (two-tail),of which the coefficient was 0.331.That means the higher of the resistance frequency, the lower of the panicle blast rate and leaf blast grade; the higher of the leaf blast grade, the higher of the panicle blast rate.5. Field resistance evaluation to blast disease showed that the blast resistance of those varieties whose father was NeiHui99-14 were different in each nurseries. In year 2010, the resistance of those varieties was poorer than that in year 2009. The blast resistance of GangYou99-14 in Pujiang,Xuyong and Yanting, and NeiXiangYou No.18 in Xuyong and Yanting in 2010 were significantly poorer than that in 2009. The resistance frequency of NeiHui 99-14 was 75.86%,56.10% and 60.83% from year 2007 to 2009, which means the resistance of NeiHui 99-14 in year 2007 was better than that in year 2008 and 2009.The resistant and susceptible single plants of C039/NeiHui 99-14 F2 group were 325 and 111 by inoculating with 04-6-8-2. The chi-square test(χ2<χ20.05=3.84) demonstrated that there was a ratio of 3:1 existing in resistance and susceptible plants (P=0.876). With the result of genotyping, the blast resistance of NeiHui 99-14 to 04-6-8-2 was controlled by a single unknown gene. As the hybrid combinations of NeiHui 99-14 were resistant to blast disease in nurseries at the beginning, the resistant gene of NeiHui99-14 to blast was dominate. |
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