[Identification and marker-assisted selection of two major quantitative genes controlling rice sheath blight resistance in backcross generations].

We constructed an F2 clonal population of intercross,Teqing/Lemont, and identified two quantitative trait loci (QTLs) contributing to rice sheath blight resistance on chromosome 9 and 11. The two QTLs were qSB-9 and qSB-11, respectively. From the population, three clonal lines were selected by markers' band types on both sides of these two QTLs, qSB-9 and qSB-11. Two were double-susceptible parent with homozygous susceptible alleles of these two loci,and the other was named as double-resistant parent,of which these two loci were all homozygous resistant alleles. These parents were separately backcrossed to recurrent parents, Teqing or Lemont. From BC2F1, marker-assisted selection was conducted in each proceeding generation and all back-crossed plants in BC2F1 and BC4F1 were inoculated by short toothpicks incubated with a strain, RH-9 of the fungus for identification of the resistance. Results suggested that these two QTLs were selected effectively in each backcross generation and their positions were also verified in identification of resistance to rice sheath blight. In seedling nursery of BC3F2 population, plants were selected through marker-assisted selection, and were separately mixed as homozygous lines of double-susceptible alleles on the background of Teqing, double-susceptible and double-resistant on the background of Lemont. The homozygous lines and their recurrent parents were simultaneously planted on experiment fields of Agriculture Collage of Yangzhou University and Lixiahe District Institute of Agricultural Science. The inoculation was performed by a random-block test with two replicates at each site. The results indicated that 1) The difference of sheath blight disease development was highly significant among materials under the same genetic background,and the order of disease seriousness among different homozygous lines were: double-susceptible line on the background of Lemont > double-susceptible line on the background of Teqing > Lemont > Teqing > double-resistant line on the background of Lemont; 2) When the resistant allele of qSB-9 or qSB-11 solely existed in a plant, its disease rating was reduced about 1.2 score, and 2.0 score when they simultaneously existed on the background of Lemont; 3) No significant interaction between the two QTLs controlling sheath blight resistance and environments was found. These studies have laid a strong groundwork in operation and application, of these QTLs contributing to rice sheath blight resistance.