| Melon (Cucumis melo L.) is a kind of important economic plants, because of its high sweetness fruit, rich nutrition and fine tasted, it became one of the world's top 10 fruits.In recent years, melon cultivation area stabilized at around 0.8 million mu, and annual output of 1.4 million tons or more. But powdery mildew has become a fungal diseases severely endangered melonn production, this caused heavy loss in main melon production area in Heilongjiang ProvinceBased on this, in the first step of this study, we monitor the trends of Heilongjiang Province powdery mildew race differentiation and succession in 2009～2010. Histopathological and ultrastructural changes of melon powdery mildew were observed after infection. Using melon varieties resistant multiple powdery mildew as study material, inheritance of the resistance of materials has been analyzed. We mapped the powdery mildew resistant gene using SSR markers. The SSR markers will be used for germplasm selection to establish molecular marker-assisted breeding system for melon powdery mildew, change the traditional methods which ruled by time, regional and plant material limitations, accelerate the breeding process, and ultimately achieve the molecular breeding of melon.The results of this study are as follows:1. Identified of powdery mildew physiological races of cucurbitaceous plant for different facilities at the major ecological zones in Heilongjiang Province in 2009-2010 using 13 differential international common melon powdery mildew races identified hosts by a common spore suspension method for inoculating. The results show that,4 races of single capsule shell powdery mildew Podosphaera xanthii appeared in Heilongjiang Province, they were, Race 6, Race 2France and unknown race, predominant species was race 1 in them.2. Studied on the pathological changes and ultra structural characteristics of melon variety Topmark during infection of powdery mildew by optical microscope and transmission electron microscopy. The results show that, Powdery mildew infection of melon can be divided into 5 stages:conidial germination, appressorium formation, haustoria generation, mycelium formation and growth, conidium formation. Pathogen produced invasion bolt and penetrated leaf epidermal cells to form a complete structure, observed under transmission electron microscopy. Host epidermal cells continue to secrete callose to the haustorial neck, and induced a substantial increase of host cell around haustorium. With the infection of pathogen, host mesophyll cells below and adjacent to infection point occurred plasmolysis, chloroplasts disintegrated, mitochondria vacuolizated, and ultimately cell wall folded, cell contents released. 3. Analyzed resistance of hybrids to single capsule powdery mildew P. xanthii race 1, powdery mildew resistant line MR-1 as female parent and susceptible line Topmark as male parent. In 2009, the resistant parent plants were immune or resistant, disease severity of susceptible parent was high, F1 resistance level slightly lower than the resistant parent, and disease manifestion was disease resistance. Resistant and susceptible segregation ratio was 1: 1 (Xc2= 0.49) in the BC1P2 population, this segregation ratio was 3:1 (Xc2=0.036) in F2 population. In 2010, resistant parent in the entire period showed immune, susceptible parent showed susceptible, plants of F1 showed high or middle resistant, resistant and susceptible segregation ratio was 3:1 (Xc2=0.28) in 145 plant of F2 population. Powdery mildew resistance phenotypes of 140 plants of F3 families suggested the ratio of F2 genotypes was 1: 2:1 (Xc2= 0.70). Comprehensive 2-year test results, the resistance to single capsule shell powdery mildew P. xanthii race 1 of MR-1 was controlled by 1 pair of dominant genes.4. In this experiment, F2 populations and F3 families has been built, powdery mildew resistant inbred line MR-1 as female parent and susceptible inbred line Topmark as male parent.2 pairs of SSRs linked to resistant gene were selected using SSR markers. Band types of the 2 pairs of primers and plant genotypes of F2 plants were input JoinMap 3.0 software for linkage analysis, the results showed that, linkage distances of the 2 pairs of primers between P. xanthii race 1 resistant gene Pm were 4. 1cM and 19.4cM respectively.5. Resistance to powdery mildew of 101 seed resources had been identified using artificial inoculation methods and molecular identification. According to the results of field identification,18 materials resistant to race 1 or 2France had been selected, in these materials there were 10 materials resistant to race 1 and 2France simultaneously. Results by application of two SSR markers identification showed that the average match rate of primers SSR04816 identification with the results of the field was 81.4%, while the average match rate of primers SSR01498 identification with the results of the field was 68.6%.This is the first time for clearing the powdery mildew race differentiation and succession in the major ecological zones of Heilongjiang Province, the first time for discovering Race 6 in China. These results provide an important theoretical basis for the study of melon and other cucurbitaceous plants powdery mildew. This is the first time for studying inheritance using 2 years multi-generation adult melon powdery mildew resistant verification data. Although time-consuming, laborious, the results are more instructive. This is the first time to report SSR marker that linkage distance less than 5 cM to single capsule shell powdery mildew P. xanthii race 1 resistant gene Pm, Using this marker to melon germplasm selection of powdery mildew resistance to to establish molecular marker-assisted breeding system for melon powdery mildew, change the traditional methods which ruled by time, regional and plant material limitations, accelerate the breeding process, and ultimately achieve the molecular breeding of melon.
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