QTL Mapping For Resistance To Verticillium Wilt In Cotton

As an important economic crop,cotton plays an important role in the economy of our country.Verticillium wilt is one of the most destructive diseases in cotton.In recent years, many cotton fields in China have been severely damaged by this disease,being recognized as a serious threat to cotton production.It has been confirmed that breeding for highly tolerant or resistant varieties to Verticillium wilt is the most effective and economical method to control this disease.However,the progress for development of Verticillium wilt resistant varieties still have some problems,there is no resistant variety in the production. Therefore,further studies about the inheritance and the molecular markers linking to Verticillium wilt resistance are needed urgently.In this study we used molecular markers to map the QTL for resistance to Verticillium wilt in Gossypium barbadense L and G.hirsutum L,and also map the QTL for the yield and fiber properties in G.hirsutum L.The results are following:1 QTL mapping for resistance to Verticillium wilt in G.barbadenseA highly tolerant to Verticillium wilt G.barbadense var.Hai7124 and a highly sensitive to Verticillium wilt G.hirsutum var.Junmian 1 were crossed and F₁ seeds produced self-pollinated F₂ progeny which comprised 128 individuals and BC₁ was produced from a cross between(Hai7124×Junmian 1)×Junmian 1.The BC₁F₁ individuals were self-pollinated to produce a BC₁S₂ population,resulting in 96 families of BC₁S₂.A genetic map included 36 linkage groups with an average distance of 7.29 cM between markers and covered 2726.89 cM was constructed using F₂ population.The F₂ individuals were inoculated with a non-defoliating isolate BP2,the disease grades were investigated at seedling and maturity stages.The mapping of the QTL and estimation of their genetic effects were performed according to the method of combination interval mapping(CIM): four QTL were detected and were located on the A5,A7 and A8 chromosome at seedling stage;three QTL were detected and were located on the A5,A7 and A9 chromosome.The contribution to phenotype of these QTL was from 8.0%to 17.1%.Another interspecific genetic linkage map including 35 linkage groups with average distance between markers of 8.65cM and covering 1772.54cM was constructed.The isolate BP2 and two defoliating isolates VD8 and 592 were used to inoculate the BC₁S₂ families.The resistance performance was investigated at seedling and maturity stages.The resistant QTL was detected using CIM method:in BP2 nursery,one QTL at seedling stage and two QTL at maturity stage were detected and they were located on D4,A8 and D4 chromosome;in VD8 nursery,two QTL located on A5 and A8 chromosome and three QTL located on A5,D5 and D11 chromosome were detected at seedling and maturity stages;in 592 nursery,three QTL located on A5 and D5 chromosome and two QTL located on D5 and D11 chromosome were detected at seedling and maturity stages.These QTL can explain the variation of phenotype from 7.8%to 22.3%.These results suggest that different resistant QTL play the role for different isolates at different stages in G.barbadense.2 QTL mapping for resistance to Verticillium wilt in G.hirsutumA resistant to Verticillium wilt G.hirsutum line 5026 and a high sensitivity to Verticillium wilt G.hirsutum var.li 8 were crossed.The F₁ seeds produced self-pollinated F₂ progeny and the F₂ progeny produced self-pollinated F_2:3 progeny comprising 154 lines.A RIL population comprising 169 lines was produced derived from the cross of 5026 and li 8. The F_2:3 lines were inoculated with the isolate VD8 and the RIL lines were departed into three parts and inoculated with three isolates BP2,VD8 and 592 respectively.The disease reaction was investigated at seedling and maturity stages in each nursery.The resistant inheritance models were analyzed using the major gene+minor gene mixed models system in the two population,the result suggests the trait of resistance to Verticillium wilt was controlled by two major genes in G.hirsutum.A intraspecific genetic linkage map including 21 linkage group with 99 SSR loci and covering 760.88cM was constructed using F₂ population.The resistant QTL were mapped in F_2:3 families using the method of CIM:three QTL were detected at seedling stage and located on LG01 linkage group and D8 and D7 chromosome;four QTL were detected at maturity stage and located on LG01 linkage and A11,D8 and D7 chromosome,these QTL can explain the variation of phenotype from 6.39%to 33.22%.The resistant QTL were mapped using RIL population:in BP2 nursery three QTL at seedling stage and one QTL at maturity stage were detected and they were located on A5,D6,D9/D10 and D11 chromosome;in VD8 nursery,two and one QTL were detected at seedling and maturity stages and they were located on A11,A8 and D9/D10 chromosome;in 592 nursery,at seedling and maturity stages three and one QTL were detected and they were located on A5,A11/D11,A8 and A5 chromosome.These QTL can explain the variation of the phenotype from 5.36%to 11.8%.3 QTL mapping for yield and fiber properties in G.hirsutumPart of each line of the RIL population were planted in the field.The corresponding traits of yield and fiber properties were investigated.The QTL for these traits were mapped by using CIM method.There were totally 11 QTL for yield traits in which 2 for lint yield,1 for seed-cotton yield,2 for fruit branches/plant,1 for bolls/plant,2 for boll weight,1 for lint percent,1 for seed index and 1 for lint index;for fiber traits there were totally 9 QTL in which 2 for fiber length,2 for fiber strength,2 for fiber elongation,1 for Micronaire,1 for fiber uniformity ratio and 1 for short fiber index.