| Powdery mildew is one of the most important disease attacking cucurbits in greenhouse and open-field. The powdery mildew physiological races infect cucurbits change quickly.Consequently, knowledge on the prevalence and geographic distribution of these races has great significances for the choice of appropriate strains, resistance breeding and prevention, using molecular-maker assisted breeding can enhance the selection efficiency and accelerate breeding of resistant variety.Compared three different methods for purifing and preserving pathogen, the result showed that preservation time was the longest by live plants, it was about three months; preservation time was the shortest by detached leaves, it was about one month; preservation time was one and half months by detached cotyledon MS medium adding hormone IAA, the best concentration of hormone IAA for cotyledon rooting was 1.5mg/l. Three methods have their advantage and dis advantage respectively, according to requirement selecting proper preservation method.Seventeen powdery mildew samples were collected and isolated from mildewed melon, cucumber, pumpkin and watermelon in greenhouse or open field of different ecological regions in Heilongjiang Province in 2010, all those samples were detected using the standard identification hosts of powdery mildew. According to performance on thirteen hosts which are universal in the world, three races on Cucurbitaceae were preliminarily confirmed which included a new physiological race, physiological races 1 and physiological race N1 of Podosphaera xanthii in Heilongjiang Province. Race 1 was the dominant race. Partial isolates of powdery mildew DNA were evaluated using Random Amplified Polymorphic DNA (RAPD) with 10 primers selected from 119 random primers. A total of 157 bands were scored, polymorphic bands were 138, the frequency of polymorphic bands was 97.89%, and it showed that high genetic diversity existed among the isolates of P. xanthii on Cucurbitaceae in Heilongjiang Province. On the basis of RAPD data analyzed by software NTSYS-PC, the similarity coefficient varied from 0.52 to 0.57 and a dendrogram was constructed using the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) method. The tested isolates were clustered into 4 groups at the similarity coefficient of 0.60, the isolates of race 1 were clustered into the same group partly, the new race was clustered into the same group with partial race 1 isolates; two isolates of race N1 were not clustered into the same group with partial race 1 isolates. The isolates of the same geographic or host origin were also not clustered into the same group. So, no obvious association was found between DNA polymorphism and pathogen races differentiations as identified by biological tests on cucurbitaceae. Also, no association was found between the results of RAPD analysis and any other of parameter tested: geographic, greenhouse type or host origin.Intergenic spacer (IGS) was analyzed for strains of powdery mildew on cucurbits using universal primers, results showed that there were length heterogeneity and polymorphism on IGS. IGS-RFLP digested by MspⅠ, AsuⅠand Hinp1Ⅰshowed that digest sites varied from the strains with profile polymorphism. The IGS-RFLP profile could become distinctive DNA fingerprint for strains. All the tested strains could be effectively identified using restrictive enzymes of MspⅠAsuⅠHinp1Ⅰ. But, no specific RFLP marker was observed between different races. On the basis of IGS1-RFLP data analyzed by software NTSYS-PC, the similarity coefficient varied from 0.46 to 0.80, the isolates were clustered into three groups at the similarity coefficient of 0.60. No obvious association was found between DNA polymorphism and pathogen races differentiations as identified by biological tests on cucurbitaceae, also no association was found between the genetic diversity and any other of parameter tested: geographic, host origin or greenhouse type. |
PDF Full Text Request