Breeding Near-isogenic Lines Of Sheath Blight Resistance In Rice

We constructed a F2 clonal population of intercross, Teqing/Lemont, and identified two quantitative trait loci (QTLs) contributing to sheath blight resistance on chromosome 9 and 11 .The two QTLs were qSB-9 and qSB-11, respectively. The located intervals were similar to those located by the two QTLs in another F2 clonal population of Jasmine85/Lemont, and the QTL ontributing to sheath blight resistance was also from Lemont. From the F2 clonal population of intercross No. 125 clone was selected as donor parent(double-resistant parent), on the chromosome 9, of which two flanking markers of the QTL(qSB-9) behaved all the same as the ones of Teqing, on the chromosome 11, of which two flanking markers of the QTL(qSB-11) behaved all the same as the ones of Lemont. No.73 and 86 clones were selected as donor parens(double-susceptible parents), on the chromosome 9, of which two flanking markers of the QTL(qSB-9) behaved all the same as the ones of Lemont, on the chromosome 11, of which two flanking markers of the QTL(qSB-11) behaved all the same as the ones of Teqing. They were separately intercrossed and backcrossed to recurrent parents, Teqing and Lemont. Beginning with BC2F1, marker-assisted selection was conducted in each proceeding generation and all backcrossed plants of BC2F1 and BC4F1 were inoculated by short toothpicks incubated with a strain, RH-9 of the fungus for identification of the resistance. In each proceeding generation, backcrossed plants were selected according to results of marker-assisted selection , disease ratings and the similarity of integrative traits between backcrossed plants and their recurrent parents. The measures ensured correctness of selected backcrossed plants. In BC3Fi, on the basis of the demands mentioned above, we gathered BC3F2 seeds of some backcrosses. AtBC3F2 generation, we selected plants of coinciding requirement of part backcrossed crosses according to the demands mentioned above and separately mixed them as homozygous lines. Thus, double-susceptible Near Isogenic Lines (NILs) in the background of Teqing, double-susceptible and double-resistant NILs in the background of Lemont were developed. The NILs 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 done in a random-block test with two sites and two replicates in each site. The result indicated that:(1) The order of sheath blight disease development among these NILs was: double-susceptible NILs in the background of Lemont > double-susceptible NILs in the background of Teqing > Lemont > Teqing > double-resistant NILs in the background of Lemont.(2) The disease ratings of double-susceptible NILs in the background of Lemont were higher 1.2 score than those of recurrent parent(Lemont). The disease ratings of Lemont were higher 0.8 score than those of double-resistant NILs in the background of Lemont. The disease ratings of double-susceptible NILs in the background of Lemont were higher 2.0 score than those of double-resistant NILs in the background of Lemont. The disease ratings of double-susceptible NILs in the background of Teqing were higher 1.5 score than those of Teqing. Above these it indicated that when the qSB-9 or qSB-11 solely existed in a plant, disease rating was reduced about 1.2 score. When they simultaneously existed, the rating reduced about 2.0 score.(3) No significant interaction between the two QTLs controlling sheath blight resistance and environments was found. It further confirmed the reliability of qSB-9 and qSB-11 and ascertained their exact intervals on chromosomes.It further confirmed that the results of the QTL mapping for sheath blight resistance in rice were right. For example, the QTLs(qSB-9 qSB-11) for sheath blight resistance truly lied on chromosomes and their approximate intervals on thechromosomes were located; These have laid groundwork under fine mapping ,operating single QTL and QTL's clone.