Constructing Of Genetic Maps And QTL Mapping Of Powdery Mildew Resistance In Bitter Melon

The resistance to powdery mildew is a main character for bitter melon open and protected cultivation and breeding for disease resistance, the physiology basis of the resistance, genetic mechanism and QTL mapping are important sicience problems which were still not solved.Firstly, for selecting the bitter melon germplasm resource which own resistantance to powdery mildew, accelerating the progress of disease resistance breeding and discussing the physiological mechanism of bitter melon’s resistance to powdery mildew, four materials with different resistance to powdery mildew were chosen from 21 bitter melon germplasms from different origins according to two consecutive years’identification of resistance to powdery mildew to study the dynamic change of related physiological indexes and the relationship between leaf structure and resistance to powdery mildew; Then the joint genetic separation and analysis method of major gene plus polygene gentic model was used to study the inheritance of powdery mildew disease resistance in Bitter melon. For acquiring high quality bitter melon genomic DNA rapidly to study molecular marker of powdery mildew resistance gene, the best method to bitter genomic DNA extraction and the optimal leaf time for sampling were explored, the main factors influencing ISSR-PCR were optimized. Then 120 strains from F2 segregation population which generated from several generation self-cross wild bitter melon 04-17-3 and cultivated variety 25-1 were chosen as mapping group to construct bitter melon genetic linkage map through ISSR, SRAP and SSR marker; finally,120 single F2 plants and 120 F2:3 families acquired by F2 single seed descent were selected to survey the powdery mildew resistant characters, QTL mapping was carried out by constructed bitter melon genetic map. The main results of the research were as follow:1. The powdery mildew morbidity degree of bitter melon germplasms from different sources showed greater difference and diversity,28.57% for resistance,28.57% for moderate resistance,33.33% is susceptible and 9.53% is more susceptible. The resistant strains could improve the disease resistance by keeping higher chlorophyll mass fraction, and increase soluble sugar mass fraction, and improve the activity of POD, PPO, PAL,SOD, CAT and APX to eliminate H2O2 accumulated because of disease infection, keep the active oxygen content balance in plant, make the cell wall lignifications to prevent further intrusion. The waxes content of resistant cultivars is significant higher than that of susceptible one and significant negative correlation with disease index. Wax layer is an important structure barrier to resist and delay the pathogen invading.The stomatal number and hair densities of abaxial leaves are significant positive correlation with disease index. soluble sugar, The activities of PAL, PPO, POD, SOD and CAT; the content of soluble sugar and mass fraction of chlorophyll, the stomatal number and hair densities of abaxial leaves, the wax content of leaf could be used as auxiliary identification indexes of powdery mildew-resistance of bitter melon; the APX activity was not significant correlation with the powdery mildew resistance, but the correlation index was bigger and could be used as a reference index.2. The powdery mildew disease resistance genetic model fitted two major genes with additive-dominance-epistasis major genes and plus-dominant poly genes model(E1), the resistance was non-complete recessiveness to susceptibility; the additive effects of two major genes were both-12.00; two major genes showed positive partial dominance and positive superdominance, respectively; the additive effect values were all higher than the dominant effect values, the epistatic effect value (i+jab+jba+l) was negative. Heritability values of the major genes in B1, B2 and F2 were estimated as 55.14%,43.56% and 95.22%, respectively, and the heritability values of the poly genes were 16.10%,26.57% and 0, respectively, the value of environmental variation was between 4.78%-29.87%. The resistance of Bitter melon to powdery mildew disease was decided by major genes and poly genes, in which major genes were dominate and was partly effected by environmental variation at the same time. In the practice of powdery mildew resistance breeding, we should pay attention to the use of additive effect, accumulate the resistance genes in the parents, and choose in the early generations, especially the selection efficiency of F2 major genes is the highest.3. The genome DNA extracted from the top leaves of bitter melon gourd by improved CATB method were pure and had good quality, the effect was better. The optimal system was 2.5μL 10×PCR buffer,2.5 mmol/L MgC12,250μmol/L dNTPs,10 ng genomic DNA,0.75 U Taq DNA polymerase,0.7μmol/L primers, and the total volume of the reaction was 25μL, the most compatible annealing temperatures of primer UBC826 was 53℃.4. The total length of constructed genetic linkage map was 732.1 cM, including 116 loci which included 47 ISSR markers,53 SRAP markers and 16 SSR markers,13 linkage groups in all, the average map distance was 6.31 cM, basically fulfils the requests for QTL mapping. The markers number in every linkage group were 2-33, the distance was between 1.7-131.1 cM, the ratios of skewed segregation was 27.50%.5. Six QTL loci were found in F2 generation, mainly in the first, the eighth and the tenth linkage group, the rate of contribution were 0.65-12.15%, the total rate of contribution of six QTL loci were 39.02%.11 QTLs were detected in F2:3 family, there were three loci in the first linkage group and five in the tenth linkage group. The loci in these two linkage groups were more concentrated. The QTLs rate of contribution was 0.97%-12.16%. The total rate of contribution of 11 QTLs in F2:3 family was 62.86%. Six QTLs (Bz1.1/LG1,28.4cM; Bz1.2/ LG1,77.3cM; Bz1.3/LG1,116.3cM; Bz8.1/LG8,18.0cM; Bz10.4/LG10,62.5cM; Bz10.5/LG10,103.2cM)of F2(autumn of 2011) and F2:3 family(spring of 2012) were located the same loca respectively in two years. The direction of additive effect and dominant effect of six QTLs were relatively consistent.