Studies On Improving Japonica Rice Resistance To Sheath Blight And Rice Blast By Marker-assisted Selection

Rice sheath blight(SB)and blast are two most serious diseases in rice worldwide.Development of resistant variety with disease resistance gene is one of the most economic and effective approach to control diseases and reduce yield loses.Marker assisted selection(MAS)can be used to select resistance gene directly,which could largely improve selection efficiency toward disease resistance compared to the conventional breeding strategy.In our previous studies,we identified two QTLs(qSB-11HJX74 and qSB-12YSBR1)with large resistance effects on sheath blight resistance from rice varieties Huajingxian 74(HJX74)and YSBR1,respectively.However,the breeding potential for the two QTL utilized to improve japonica rice resistance remains unknown.In breeding towards blast resistance,we found that some reported genes with broad spectrum resistance to blast disease,like Pigm and Pi40,are rarely used in japonica rice breeding.In this study,we employed MAS to introduce qSB-11HJX74,qSB-12YSBR1,Pigm and Pi40 into different japonica rice varieties for evaluating their breeding potential.Results in the present study will be of great theoretical and practical significance in japonica rice breeding towards SB and blast resistance.Mainly results are as follows:1.The qSB-11HJX74 was introduced into different japonica rice cultivars through MAS.Different BC1F2 rice populations from backcrosses between the qSB-11HJX74 donor parent and each of recurrent parents(RP),Lianjing 6,Yanfeng 47,Jijing 88,and Liaojing,were inoculated with SB pathogen at seedling stage.Results showed that disease scores of BC1F2 plants with qSB-11HJX74 homozygous genotype(hereafter called qSB-11HJX74)were all significantly lower than that of plants with heterozygous genotype(hereafter called qSB-11H)and with homozygous RP genotype(hereafter called qSB-11RP)in qSB-11 locus.Also,no significant difference was found between qSB-11H and qSB-11RP plants on disease scores.These indicate that qSB-11HJX74 is a recessive resistance allele to SB disease.In the backcrosses between qSB-11HJX74 donor parent and Nangjing44,liangjing6 and Liaojing,we obtained some BC1F3 lines with qSB-11HJX74 and found their resistant level significantly higher than the corresponding recurrent parent with around 1.0 difference on disease scores.These indicate that qSB-11HJX74 is able to improve SB resistance of japonica rice varieties tested.Further,we observed some agronomical traits of advanced backcross lines in background of Nanjing 5055 and Nanjing 9108,and found the introduction of qSB-11HJX74 has no inferior effects on the agronomic traits tested.2.The qSB-12YSBR1 was introduced into different japonica rice cultivars through MAS.Different BC1F2 rice populations from backcrosses between the qSB-12YSBR1 donor parent and each of RPs,Nanjing5055,Nanjing9108,liangjing6,Nanjing44 and W030,were inoculated with SB pathogen at seedling stage.Results showed that no significant difference on disease scores was found between BCiF2 plants with qSB-12YsSB1 homozygous genotype(hereafter called qSB-12YSBR1)and plants with heterozygous genotype(hereafter called qSB-12H),while all signif1cantly lower than the plants with homozygous RP genotype(hereafter called qSB-12RP)in qSB-12 locus.This indicate that qSB-12ySBR1 is a dominate resistance allele to SB disease.In the backcrosses between qSB-12YSBR1 donor parent and Nangjing9108,Nangjing44 and W030,we obtained some BC1F3 lines with qSB-12YSBR1 and found their resistant level significantly higher than the corresponding recurrent parent with around 1.0 difference on disease scores.These indicate that qSB-12YSBR1 is able to improve SB resistance of japonica rice varieties tested in the present study.3.Through MAS we introduced Pi40 and Pigm into two susceptible varieties Taijing1152 and Yangyujing116,respectively.In BC2F3 generation,we obtained some lines with homozygous genotype in either Pi40 or Pigm locus.Twenty blast isolates from different regions of Jiangsu were used to inoculate these BC2F3 lines,and we found that rice lines with either Pigm or Pi40 all showed enhanced resistance spectrum compared to original parents.In national natural blast disease nursery of da wei shan,we found lines with Pigm generally displayed stronger resistance than that of lines with Pi40 in seedling stage,while no apparently difference was observed in resistance to neck blast.By using mixed blast strains from 2017 jiangsu rice variety identification test,we found that lines with Pigm generally displayed stronger resistance to neck blast than that of lines with Pi40.Taken together,we believe that both resistance genes are of breeding potential in developing Jiangsu japonica rice variety towards blast resistance although Pigm probably showed more broader spectrum or stronger resistance than Pi40.