Establishment Of Watermelon And Melon Genetic Transformation System And Analysis Of Disease-resistance In Transgenic Plants

It is a major reason that the yield losses and quality worsen of plants due to fungal attack limits crops productivity and could be very severe local epidemic infections. The watermelon [Citrullus lanatus (Thunb.) Mantsum.et Nakai] and melon (Cucumis Linn.) are an important fruit, China is first country in their productivity and planting area in the world. The main problems existing in the production of melon are the diseases caused by fungi endanger especially. However, because of narrow resistance genetic resources and complicated hereditary of resistance of melon, conventional melon breeding is limited. In the past decade, transferring antifungal protein genes into plants have become a most direct and efficient way to obtain fungi resistant plants that has attracted many researchers'attention. A number of studies demonstrated that the tissue culture of melon is more difficult than other plant species, and the optimization of genetic transformation system is more complicated which results in very lower transformation frequency of melon. Rercently, the disease-resistant genetic engineering of plant makes great progress in the improvement of some important plant species. However, only a few of studies are involved in the melon disease-resistant transformation.In this thesis, we have studied the effects of tissue regeneration of watermelon and melon, optimized Agrobacterium tumefaciens-mediated transformation procedure of the two important crops. The three antifungal genes, chitinase gene (CHI), beta-1, 3- glucanase gene (GLU) and THI gene, were isolated from tobacco and wheat, respectively. A plant expression vector carrying the three genes was constructed. After transformation, 9 transgenic melon lines and 7 transgenic watermelon lines were obtained and then used for further molecular biology analysis and disease-resistance identification. The main results are as follows:1. The optimization of watermelon and melon regeneration systemâ‘ The regenerated buds could be produced easily and directly from stem apex and cotyledon explants, but not from leaves and stem explants.â‘¡Using the MS medium as the basic medium and cotyledon as explants, an efficient regeneration system of watermelon and melon was established. The optimized regeneration medium for cotyledon is MS medium supplemented with 1.0 mg/L 6-BA and 0.5mg/L IBA for watermelon, and 2.0mg/L 6-BA and 0 .5mg/L IBA for melon. The regeneration frequencies were 91.2% and 94.3% in watermelon and melon, respectively.