Genetic Study On Inheritance Of Clubroot Resistance In Resynthesized White Flower Brassica Napus.L

In this paper,the six populations(P₁,P₂,F₁,BC₁,BC₂ and F₂) of the cross between a common Brassica napus variety Zhongyou 821(P₁) and a resynthesized Brassica napus line HW243(P₂) were planted in natural disease nursery(Kangding,altitude 2650m) to study the inheritance of clubroot resistence.The clubroot resistence was observed with four levels,respectively.And the genetic rules of clubroot resistence character were analysed.Based on the absorbances in P₁,P₂,F₁ and F₂,the relationship between petals color and clubroot resistence was determined with the pigment abstraction methods of flower petals.BSA(bulked segregant analysis) was used to identify the SSR and RAPD molecular markers linked to the clubroot resistence character in the combination 'Zhongyou821×HW243'.The main results were summarized as follow:1.The results showed that P₁ were highly susceptible to clubroot,P₂ and F₁ were highly resistant.Two types phenotypes were observed in the segregation of BC₁ and F₂ populations.The ratio of resistant and susceptible plants in BC₁ was 1:1 (P=0.3-0.5),and the ratio of resistant and susceptible plants in F₂ population was 3:1 (P=0.95-0.99).In BC₂ all plants were resistant.It was shown that the resistant character in the resynthesized B.napus line HW243 was controlled by a single dominant gene for resistance to clubroot.2.Observations showed that there was no obvious difference in flower color between the reciprocal F₁ hybrids.The petal color of F₁ hybrids was milky,slightly inclined to the white flower parent.We used absolute alcohol as the solvent for the systematic investigations in this experiment.The extracted solutions were tested with the wavelengths 439nm and 469nm.Based on the absorbances in P₁,P₂ and F₁,the values in F₂ could be classified into 3 groups,i.e.,0-0.150(close to white flower P₂), 0.1-0.500(close to milky flower F₁,RF1) and 0.500-2.000(close to yellow flower P₁). With Chi-square test,the ratio of white:milky:yellow flowered plants was 1:2:1 in the F₂. 3.combined analysis of petals color and clubroot resistence shows that six phenotypes were observed in F₂.The six phenotypes was 'white flower and resistant plants','milky flower and resistant plants','yellow flower and resistant plants','white flower and susceptible plants','milky flower and susceptible plants' and 'yellow flower and susceptible plants',The ratio of each phenotype plants was 3:6:3:1:2:1 (P=0.10-0.20).It is suggested that no significant negative correlation exists between the petal color and the clubroot resistence.The petal color can't be morphological marker of clubroot resistence in the resynthesized B.napus line HW243.4.With 600 pairs of SSR primers the DNA molecular polymorphism was tested in the cross combination 'Zhongyou821×HW243'.114 pairs of SSR primers produced polymorphism between the two parents.The percentage of polymorphic SSR markers was 19%.By using 10 recessive individuals of F2 population,SSRol10-F09₁₂₅ was found linked to resistance gene.340 RAPD primers were amplified between the resistance pool and susceptible gene pools of the F2 cross of zhongyou 821×HW243. Out of the primers,only SBS-A08(5′-GTGACGTAGG-3′) showed polymorphism between gene pools and the parents also had the same polymorphic markers on the same locus.A polymorphic fragment of 470 bp by amplified by SBS-A08 primer was designated as SBS-A08₄₇₀ and found linked to resistance gene.5.The PCR results amplified by the two primers of these F2 population which had two hundreds individuals were analyzed by using MAPMAKER/EXP(VERTION3.0) software.The results indicated that SSRol10-F09₁₂₅ and SBS-A08₄₇₀ linked with the gene of clubroot resistance and located at the same side of the gene.The genetic distance between SSRol10-F09₁₂₅ and the gene was 15.6cM,the genetic distance between SBS-A08₄₇₀ and the gene was 8.3cM.