Researching On Effects Of A Resistance QTL (qSB-11～(Le)) Against Rice Sheath Blight And Its Fine Mapping And Candidate Gene Analysis

Sheath blight, caused by Rhizoctonia solani k¨1hn, is one of the major diseases of rice worldwide, and causes severe loss in yield and quality under favorable environmental conditions. Rhizoctonia solani is a semi-necrotrophic pathogen fungus and has a very wide host range including rice, wheat, soybean, corn and so on. In many regions of southern China, sheath blight has become the most destructive disease in rice. However, comparing with the other two rice diseases, bacterial blight and blast, the resistance to sheath blight is a typical quantitative trait, and strong sources of resistance with major genes in rice against this disease are not available. Consequently, identifying the quantitative trait loci (QTL) conferring the resistance to this disease in some rice cultivars not only presents the significance in practical breeding use but also provides the insights into the mechanism for quantitative resistance.So far, up to 30 QTLs that confer the resistance to rice sheath blight were detected to scatter on all 12 rice chromosomes from several mapping populations. Among them, one QTL as qSB-11 was identified in several populations and/or environments. The resistant allele as qSB-11Le underlying the qSB-11 came from a relatively susceptible japonica rice cultivar, Lemont, while the relatively resistant indica rice cultivars, Teqing, possessed the susceptible allele as qSB-11Tq. From the previous studies,the longest probability interval of qSB-11 was estimated from the molecular marker RM167 to G44, covering the positions of the markers, RG118 and RM202. Notably, in this probability interval, no QTLs conditioning the other traits, such as the plant height and heading time, which were regarded as the important affection factors for the development of SB, were identified. All above results indicated that the qSB-11 was a veritable QTL conferring the resistance to sheath blight. Consequently, the qSB-11 was further investigated in the present study.By marker-assisted selection (MAS), one BC4F1 backcross plant was selected in BC4F1 population derived from the Lemont (recurrent parent) and Teqing (donor parent).