Enhancement Of Plantlet Regenerative Efficiency And In Vitro Tetraploid Induction In Watermelon(Citrullus Vulgaris Schrad.)

Watermelon (Citrullus lanatus Schard.) is an important fruit crop that is widely cultivated throughout the world. It ranks one of the top ten fruit crops and favored by consumers for its special flavor and juicy flesh. Especially the triploid watermelon is increasingly popular with consumers and growers largely attributed to its high quality, convenience of seedlessness and long shelf life. However, the production of seedless triploid watermelon is limited as a result of many factors, one of which is the low efficient and laborious way of producing tetraploids. High shoot regenerative efficiency of diploid watermelon is important for induction of tetraploid watermelon. So we did two experiments to get high induction efficiency.The purpose of the first study was to enhance shoot regenerative efficiency of watermelon by optimizing culture parameters. Cotyledons at 5-day seedlings were explanted and cultured on VIS medium supplemented with different combinations of hormones. In 'Yixuan' cuitivar, the plantlet regenerative frequency and shoots produced per explant was as low as 1% and 0.4 respectively at all combinations tested when distal parts of cotyledons were inoculated. Whereas, maximum regenerative frequency of 100 percentage and 10.3 shoots regenerated per explant were observed on MS medium supplemented with 5 mg/L BA and 0.1 mg/L IAA using basal parts of cotyledons as explants. Likewise, in 'Jingxinmuben' cuitivar. the highest regenerative frequency of 100 percentage and 6.9 shoots regenerated per explant were obtained when proximal pans of cotyledons were cultured on MS medium containing 2 mg/L BA and 0.5 mg/L IAA. In the present study, adventitious buds were initiated after only 4 d in culture and intact plantlets were obtained in 40 d culture. This will facilitate quicker gene transformation and polyploid induction of watermelon in vitro.The purpose of the second study is to improve watermelon tetraploid induction in vitro byoptimizing culture parameters. The results of colchicines test showed that liquid treatment is more appropriate and efficient in inducing tetraploid than the conventional solid treatment. In liquid treatment, the highest shoots regenerative rate, survival rate and tetraploid percentage were obtained (100%, 84.3% and 57.1%, respectively) when explants were treated with 200mg/l colchicine for 12 h. In contrast, in solid treatment, maximum results were achieved (73.3%. 78.6% and 55.6%, respectively) in the three indices aforementioned when treated with 200mg/l colchicine for 12 h. Moreover, explants showed better response to preculture prior to their subjection to colchicine. The best duration tested for preculture is 5-day in which both survival rate and tetraploid frequency were maximum at 95.2% and 66.7% respectively. The putative tetraploids were successfully identified from the population of regenerants by conventional chromosome counting and this was further confirmed by chloroplasts number of guard cells. Then we use herbicide oryzalin to induce tetraploid, the results showed, liquid treatment is more appropriate and efficient in inducing tetraploid than the conventional solid treatment, but survival rate in solid treatment is higher than that in liquid treatment( 68.2% and 53.7%, respectively) Finally, We tried to study cDNA-RAPD reaction to differenciate diploid and tetraploid and affection of the culture condition on diploid and tetraploid to indentify them.