| Watermelon (Citrullus lanatus) is an important fruit crop. It ranks one of the top ten fruit crops and its yield ranks the third vegetable varietes crops, and it plays an important part in people's life. Triploid seedless watermelon was favored by consumers; however, the production of seedless triploid watermelon is limited as a result of many factors, one of which is the low seed production of tetraploids. To acquire higher seed producing is the key to breed good triploid.Several single factor tests were first done in dipoid germplasms on colchicines concentration, processing temperature, topping states, treatment time in the experiment, and orthogonal tests of three lelvels four factors were done base on single factor tests. The results are as follows:1. The different colchicine concentration treating tests showed that: the lower the colchicines concentration was, the higher the seedling survival rates were. The seedling survival rates reached to the highest 96.51% when the colchicines concentration was 0.1%, and when the colchicines concentration were 0.4%, the seedling induction frequency reached the lowest 91.05%. The induction frequency reached highest 10.47%, when the colchicines concentration was 0.3%, and when the colchicines concentration were 0.1%, the seedling induction frequency reached the lowest 0.65%.2. The different tempreture treating tests showed that: the higher the temperature was, the the higher the seedling survival rates were. The seedling survival rates reached to the highest 94%, when the tempreture was 18℃, and when the tempreture were 12℃, the seedling survival rates reached the lowest 85.85%. The induction frequency reached highest 21.56% when the tempreture was 18℃, and when the tempreture were 12℃the seedling induction frequency reached the lowest 13.08%. There were some differences among different dipoid germplasms: Jing fu-2 and M08 recahed their highest induction frequency when the temperature was 15℃. However the early mature germplasm (Hong xiaoyu) recahed their highest induction frequency when the temperature was18℃. 3. The different topping states treating tests showed that: the bigger the plants were, the the higher the seedling survival rates were. When the topping states were 1, the seedling survival rates reached the lowest 88.40%. When the topping states were 4, the seedling survival rates reached the highest 97.50%. There were significance differences among different treatments. There was great difference after topping, when the topping states were 1 the induction frequency reached highest 20.98%. When the topping states were 1, the induction frequency reached lowest 3.64%.4. The different timing treating tests showed that: the longer the treating was, the the lower the seedling survival rates were. The seedling survival rates reached to the highest 96.84%, when the time was 5 days, and when the time was 7 days the seedling survival rates reached the lowest 74.80%. The induction frequency reached highest 13.96%, when the time was 5 days, and when the time was 4 days the seedling induction frequency reached the lowest 5.08%.5. The orthogonal test results show that: the seedling survival rates were high after treating and most of the seedling survival rates were about 90%. The highest seedling survival rates reached 98.33% which was treatment 5, which topping state wasthree-leaves, treating time was 4 days, colchicines concentration was 0.3%, processing temperature was15℃. The seedling survival rates can reach 100% in some treatmens. The best treatment for induction frequency was 4 which reached 25.33%. The topping state was three-leaves, treating time was 4 days, colchicines concentration was 0.3%, processing temperature was15℃. The later mature germplasm (M08) reached its highest induction frequency 46%.6. By the range analysis results of orthogonal tests we can see the influence to the seedling survival rates were topping states>temperature>treating time> colchicines concentration. The best seedling survival treatment combination was that when topping statewas three-leaves, treatment time when 6 days, colchicines concentration was 0.3%; processing temperature was 18℃.7. By the range analysis results of orthogonal tests we can see the influence to polyploid induction rates were: treating time>topping states>treating temperature> colchicines concentration. The best seedling polyploid induction combination was that when topping state was two-leaves, treatment time was 5 days, colchicines concentration was 0.3%, processing temperature was18℃.Several shortcut methods were used in seedling polyploidy identification. First of all morphological identification (leaf area, vine length and the stem diameter) was carried through then use the biological character identification (leaf pore diameter, chloroplast number in the guard cell, content of chlorophyll, unit area moisture content), at last further polyploid identification was carried by pollen mother cell chromosome. Morphological observation was the moet simple method in the polyploidy identification, and the chromosome counting method can be used in some uncertain ones.
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