| Melon diseases have been spreading rapidly and have resulted in disaster in yield of melon, resent years. Especially, downy mildew and Fusarium wilt of fungus diseases have high outbreak frequency and threatened melon production seriously. The two diseases always lead to marked losses in many areas, even harvested nothing at someplace. The main methods to prevent downy mildew and Fusarium wilt are using chemical pesticide which brings about potential danger to health of people and environment. To breed resistant lines which are fit for planting takes up agriculture workers many years, And it is always slower than the development of pathogen. There are a few melon lines with resistant ability, although most of melon lines are susceptible. Now, it is important to exploity disease resistance genes in melon and to improve resistant ability of melon by transferring these genes into some melon lines. Huangdanzi has a high disease resistant ability and is always used as parents in breeding. We selected Huangdanzi as material to clone cDNA sequences relating to resisting downy mildew and Fusarium wilt. Another resistant line-Jinli-2 and two susceptible lines-Jiashi, Hongxincui were comparison materials in experiment. Firstly, picked Fusarium oxysporum melonis and Pseudoperonospora cubensis and infect melon seedling. Extracted total RAN from melon leaves after infection 0, 6, 12, 24, 48h and performed on RT-PCR to isolate target cDNA sequence. Five pairs primers were designed and based on conserved motifs of known plant disease resistant genes to clone gene relation to resisting downy mildew, and one pairs primers were come into based on Fom-2 cloned in order to obtain gene about resisting Fusarium wilt. And two important cDNA sequences were isolated. One of them was named mp-19, and the other was named X-Fom-2. Then genomic DNA was hybridized with mp-19 cDNA probe labeled by DIG. The bands were detected by screening resistant or susceptible melon traits genomic DNA hybridized with probe. This hinted that any melon lines contained mp-19 DNA sequence. Semi-quantitative RT-PCR showed that mp-19 expression was enhanced by Pseudoperonspora cubensis infection in resistant melon-Huangdanzi. However, the expression level was very low in susceptible melon-Jiashi either infected by Pseudoperonspora cubensis or not. We concluded that mp-19 gene might be concerned with the downy mildew resistance in melon. Southern blotting and Northern blotting were carried out to analyze the characters of X-Fom-2. And the results were similar to analysis about mp-19. We had the conclusion that X-Fom-2 was a partial-length sequence of Fusarium wilt resistant gene. From above all, it was known that the keys to resist downy mildew and Fusarium wilt were that mp-19,X-Fom-2 coμld express but not just existed. mp-19,X-Fom-2 could be bases of cloning of their whole-sequences by two methods they were RACE and isolation from melon genomic libraries. And we would breed resistant lines by genetic transformation. We also could isolate promoters of mp-19, X-Fom-2 and study machine of the genes'expression and how to resist corresponding to diseases. Furthermore, mp-19, X-Fom-2 were used as markers relating to preventing melon from infecting by Fusarium oxysporum melonis and Pseudopero-nospora cubensis respectively. And they would be the good tools in breeding of melon, in order to avoid wasting time.
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