| Rice(Oryza sativa L.)is used as the staple for around 50 % of the world population.However,its production is hampered by abiotic and biotic stresses.The rice blast caused by Magnaporthe oryzae fungus is the most devastating rice disease.Since genetic resistance in rice may come with a penalty in the yield,utilization of gene resources for rice breeding will be made easier by preventing linkage drag between yield traits and blast resistance genes.Previous studies indicate that the Pi26-Pi25 resistance gene cluster in rice had a linkage drag with yield traits,which may be avoided in the presence of functional alleles at the Ghd7 locus for heading date.This thesis was conducted to test this assumption and to study the genetic relationship between blast resistance and yield traits in rice.A population consisting of 256 recombinant inbred lines(RILs)was constructed from a cross between indica rice restorer lines Dan 71(D71)and Zhonghui 161(ZH161).The two parents both carried functional Ghd7 alleles,but they had contrasting genotypes for blast resistance genes Pi26,Pi25,Pib,and Pita.The maternal line D71 carried a susceptible allele at Pib but resistance alleles at the other three loci.The paternal line ZH161 carried a resistance allele at Pib but susceptible alleles at the other three loci.The RIL population and two parents were planted in a paddy field for evaluating yield traits in 2019 and 2020,and also tested in a greenhouse for leaf blast resistance(LBR)in 2020 using a mixture of 14 predominant fungi isolates.Eight yield traits were measured,including grain yield per plant(GY),number of panicles per plant(NP),number of spikelets per panicle(NSP),number of grains per panicle(NGP),1000-grain weight(TGW),grain length(GL),grain width(GW),and the ratio of grain length to grain width(RLW).The maternal line D71 was highly resistant to the blast disease,whereas the paternal line ZH161 was susceptible.D71 and ZH161 showed no significant difference in NP,but the trait values of GY,NGP,and TGW were all significantly higher in D71 than in ZH161.In the RIL population,a bimodal distribution of major-gene inheritance was observed for LBR,while all eight yield traits showed continuous distributions of quantitative inheritance.A high-density linkage map consisting of 1246 DNA markers was constructed,spanning 1798.1 c M with an average distance of 1.5 c M between adjacent markers.This map was employed for QTL mapping using QTL Ici Mapping 4.1.A total of 75 QTLs were identified,including 2 for LBR and 73 for the eight yield traits.The two QTLs for LBR were closely linked and located in the Pi26 and Pi25 regions,explaining 69.06 % and 12.73 % of the phenotypic variance,respectively.The alleles for enhancing blast resistance were both derived from the resistance parent D71.In regions covering Pi26 and Pi25,QTLs were detected for grain yield and its component traits.All the alleles for enhancing grain yield were also from D71.Not only was the linkage drag due to Pi26 and Pi25 avoided,but the results also indicate that these genes/QTLs may be used for simultaneously enhancing blast resistance and grain yield in rice.In the Pib and Pita regions,QTL was not detected for blast resistance but was for yield traits.In each region,the allele for improving trait performance was derived from the parent carrying the resistance allele,indicating that these genes/QTLs may also be used for simultaneously enhancing blast resistance and grain yield in rice.In this study,the majority of the QTLs detected for yield traits were located in clusters.Among them,12 clusters for grain weight and size were close to or contained cloned genes for the same trait.On the other hand,four QTL clusters for grain weight and size,q GL4/q GW4.1,q GL11.2/q RLW11,q TGW11/q GW11,and q GL12/q GW12/q RLW12,were located in regions away from the cloned genes.They could be used as candidates for map-based cloning. |
PDF Full Text Request