Genetic Analysis And QTL Mapping Of Downy Mildew Resistance In Cucumber

Cucumber(Cucumis sativus L.)is one of the main varieties of vegetables in China.Downy mildew,caused by [Pseudoperonospora cubensis[(Berkeley &M.A.Curtis),Rostoyzev],has a rapid and serious impact on the yield and quality of melon,which is a destructive leaf disease in the production of cucumber.Application of chemical pesticides as the main method for the prevention and treatment of the disease can bring environmental problems and safety issues,therefore the breeding for resistance of cucumber downy mildew is undoubtedly the most effective solution.The inheritance of resistance to cucumber downy mildew and the localization of resistance gene will help to guide the downy mildew resistance breeding process.Six generations of P1(IL112),P2(HNAU0023),F1,P1BC1F1(B1),P2BC1F1(B2),F2 derived from a crossing between parent ‘IL 112',which was susceptible to DM(downy mildew)and parent ‘HNAU 0023' with high resistance for DM,were applied for genetic analysis of downy mildew resistance in cucumber by SEA-G6.Secondly,a linkage map for RIL population(HNAU0023×IL112)with 190 F6 families was constructed with 672 SSR markers,which was published homogeneous distribution in cucumber genome.QTL analysis of the resistant to cucumber downy mildew was performed by inclusive composite interval mapping(ICIM).The main results are as follows:(1)Six generations of P1,P2,F1,B1,B2,F2 derived from a crossing between parent‘IL112' and HNAU0023 were used for natural inoculation and identification in three times,the results shows that: The disease index of F1 population were between the two parents,tend to susceptible parents,and the absolute value of the kurtosisand and the skewness of the separation groups B1,B2 and F2,in three experiments,were less than 1 and normal distribution.The results of three times indicated that resistance of HNAU0023 was inherited by the quantitative trait of the recessive gene.(2)Applicating the method of a mixed genetic major gene plus polygene inheritance model of quantitative trait in plants to study the inheritance of the resistance for downy mildew in cucumber.Results shows that: In experiment ?the best model of the resistant to cucumber downy mildew was E-0 model(two pair of additive-dominant-epistasis major gene plus additive-dominance-epistasis polygene),and the heritability of the major gene in B1,B2,F2 population was 68.63%,76.36%,87.15%,and heritability of the polygene was 0%,7.25%,0%,therefore,Separate generations were dominated by major gene.The inheritanceof cucumber downy mildew resistance followded “E-1”models(two pair of additive-dominant-epistasis major gene plus additive-dominance polygene)in experiment?.Heritability of the major gene in B1,B2,F2 population was 68.49%,9.9%,69.01%;Heritability of the polygene was 0%,54.68%,1.04%.Heritability of the major gene was higher than the polygene besides B2 population.In experiment ?,the inheritance of cucumber downy mildew resistance followded “D-0” models(one pair of additive-dominant major gene plus additive-dominance-epistasis polygene).Heritability of the major gene in B1,B2,F2 population was 4.09%,2.9 3%,1.57%;Heritability of the polygene was 0%,54.68%,1.04%,and heritability of the polygene was higher than the major gene.Three experiments showed that inheritance of downy mildew resistance was affected by genetic factors greater than environmental influences besides B2 in experiment ?,Although the optimal genetic model and genetic parameters were different of three experiments.the inheritance of the resistance for downy mildew in cucumber was controlled by “two(or one)major gene plus polygene”.(3)In total,672 SSR primers were used for polymorphism screening between two parents and resistant-suspect pool,74 pairs of SSR primers with good polymorphism and clear bands were obtained.Excluding one marker showed serious distorted segregation,73 SSR markers were selected to construct a genetic linkage map contains 7 linkage groups.The minimum linkage group was 51.22 c M,and the maximum was 190.84 c M,length of the lingkage map was 969 c M with an average of 13.27 c M.(4)5 QTLs of downy mildew resistance were detected by using the method of ICIM,and they were respectively located in the linkage groups of 1(2),5(2),and 7(1).Dm5.1,relatively stable,was detected in three experiments and located between UW083711 and UW085350,could explain 3.23-17.67 % phenotypic variation;dm1.1 and dm5.2 were detected in the experiment ? and ?,could explain the phenotypic variation of7.31-27.54 %,12.94-17.33 %,respectively;dm1.2 and dm7.1 were detected only in experiment ?,and has low contribution rate.In summary,dm1.1?dm5.1?dm5.2 was the main locus in three experiments.