The Study Of Genetic Resistance Of Melon To Downy Mildew (Pseudoperonospora Cubensis) And SRAP Marker Of The Resistant Gene

Downy mildw[Pseudoperonospora cubensis(Berk.et Curt.)Rostov]is an important disease in the production of melon In hot and humid conditions, it has a direct impact on the yield of melon, sugar content in fruit and commodity rates because prevention and control of the downy mildew are very difficult. In recent years, the occurrence and damaged area of downy mildew has expanded each year with the continuous expanding of melon's cultivation in our country, especially melons cultivated in the protected field which have a heavy loss. Currently pesticides are mainly used to prevent the occurrence of downy mildew in production, however the long-term use of pesticides not only pollutes the environment, but harm people's health as well, it is a great practical significanc in developing the new disease-resistant variety, therefore, to dissect the inheritance law of the melon's resistance to the downy mildew.The germplasm DM3of highly resistance to downy mildew and the germplasm DF4of highly susceptible to downy mildew as parents were used to construct F2segregating populations and BC1backcross progenies so as to study the inheritance of downy mildew of melon. And the SRAP method combining with the BSA method were used to find the molecular markers linked with downy mildew resistant gene to assist breeding. Moreover, the activity changes of peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were investigated in the resisitant and susceptible parents after infected with downy mildew. The main results as follows:(1) The germplasm DM3of highly resistance as female parent and the germplasm DF4of highly susceptible as male parent, The F1performanceed susceptible. The survey showed that114plants performanced susceptible and42plants performanced disease-resistant which were closed to segregation ratio of3:1in the F2population of156plants; The survey of60BC1population which F1backcross with DF4found that disease-resistant plants were6and susceptible plants were54which were closed to segregation ratio of0:1. The survey of61BC1population which F1backcross with DM3found that disease-resistant plants were37and susceptible plants were24which were closed to segregation ratio of1:1. It indicated that the resistance of female melon parent DM3to the downy mildew was controlled by one pari of recessive gene.(2)273pairs of SRAP primers were used to screen in resistant and susceptible pool respectively,3140bands were amplified out and each pair of primers amplified11.5bands evenly. There was one pair of primer me8em11which performanced stably polymorphism in the resistant and susceptible pool.107plants had been detected this band and in other49plants did not appear this band in the156F2populations. Used JoinMap3.0software for linkage analysis, the result showed that linkage distance between the mark and the downy mildew resistance gene was9.8cm.(3) The activity of POD, PPO and PAL in the resistant and susceptible varieties had a relatively obvious changes after inoculated. POD of the resistant and susceptible varieties trended increased first and then decreased. PPO on the contrary, first decreaseed and then increased, PAL did not change significantly in the first four days after inoculation,the upward trend begined from6th days of the inoculation.