| Rice sheath blight (SB) caused by Rhizoclonia solani (R. solani) is one of the most serious diseases worldwide, causing bad quality and serious yield loss under SB disease severely development. In the present study, we firstly investigated the effects of different SB disease development levels on grain yield and lodging resistance, and then analyzed the prospect of using resistance QTL to improve Japonica rice resistance to SB and ultimately to reduce yield loss from SB disease. The main results were as follows:1. Effects of different SB disease development levels on some yield-associated traits and lodging(1) By using 16 Japonica rice varieties widely planted in Jiangsu province, we measured the plant yield and its components were measured under differently diseased levels after artificial inoculation. Results indicated that, the grain yield of plants/tillers with SB rating scores ranged from 5.0 to 6.0 was apparently lower than that of plants with SB scores less than 3.0, which was reflected by the decrease of two yield components,1000-grain weight and seed set ratio. The same trend was found among varieties tested.(2) Three Japonica rice varieties with different heading date were planted in large scale in field, and two of them were artificially inoculated and the other was planted in SB disease heavily developed field. The plant yield and its components with SB disease scores from 0 to 7 were measured, respectively. Results indicated that the seed set ratio,1000-grain weight and panicle weight were all found decrease with the rise of SB scores except for the seed number per panicle. No significant difference was found among the plants with SB disease scores less than 4; while, significant difference was found between the plants with SB scores of 5 and of 4. Once the SB scores exceeded 5, the grain yield was found apparently decrease with the rise of SB scores.(3) The stem lodging resistance of 4 Japonica rice varieties was measured under three disease conditions, SB disease of 0,5 and 7. Results indicated that, for all varieties, the stem lodging resistance of plants with SB scores of 5 significantly stronger than that of plants without disease; and for 3.0 of 4.0 varieties, the plants with SB scores of 5.0 showed significantly stronger lodging resistance than that of plants with SB scores of 7.0. These results demonstrated that, for most varieties once the SB disease developed more than scores of 5.0, their lodging resistance would decrease significantly. Undoubtedly, under this condition if the rice plants meet disadvantage weather condition they would fall easily and cause serious yield loss.2. Improve of Japonica rice resistance to SB disease by QTLs via marker assisted selection (MAS)Two SB resistance QTLs, were introduced into Nangjing5055 (NJ5055), Nangjing44 (NJ44) and Nangjing9108 (NJ9108), respectively, through MAS. Results indicated that:(1) in the genetic background of NJ44 and NJ9108, the homozygous qSB-9TQ gene was able to reduce SB disease score of around 1.0; (2) in the genetic background of NJ5055 and NJ9108, the homozygous qSB-11HJX74 gene was also able to reduce SB disease score of around 1.0, while no clearly resistance effect was observed in heterozygous status of qSB-11HJX74, suggesting the recessive genetic mode of qSB-11HJX74; (3) the two genes were pyramided in the genetic background of NJ9108, which was found to reduce SB disease scores of 1.83, significantly larger than that of harboring either of them. Currently, most Japonica rice varieties showed susceptible to SB disease with SB scores of more than 6.0, which indicated that we can employ SB resistance QTLs to control the disease severity less than SB scores of 5.0. Consequently, in the current status, we believe that it is feasible to improve SB resistance of Japonica rice variety and reduce the yield loss from SB disease by pyramiding SB resistance QTLs.Taken together, these results allowed us to further understand the effect of SB disease on rice and to set an appropriate breeding effort for SB resistance in the current stage. |
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