Establishment Of Indirect Regeneration System In Virto And Iduction Of Somaclonal Variation For Enhanced Cold Tolerance In Watermelon (Citrullus Lanatus)

Watermelon (Citrullus Lanatus) originates from Africa, and are hot and draught tolerant. However, watermelon is sensitive to cold stress and is devoid of the germplasm that is tolerant to cold. Watermelon can be grown almost all over the world, but its growing largely limited seasonally. Therefore, it is urgent need to improve watermelon economically important traits by using biotechnology.More and more watermelon researchers begin to improve watermelon germplasm by biotechnology, such as meristem culture, protoplast culture, somatic hybridization, gene transformation and somaclonal variation. Currently somaclonal variation is still through direct regeneration system. If an indirect regeneration system of watermelon is established, the frequency of somaclonal variation could be improved, and the chance of obtaining useful variation will be increased. It has been indicated by experiments that plant organs or tissues used in vitro culture will react like intact plants by inducing correlative genes expression.In this study, we have established the indirect regeneration system for watermelon by which candidate plants cold of tolerance were obtained by applying cold stress during somaclonal variation.Firstly, it focused on establishment of indirect regeneration system of watermelon. The best media and the proper conditions for both callus induction and adventitious shoot differentiation have been determined. The results showed that the quality of watermelon calluses induced in dark is much better than those induced in light condition. Among the 18 media used for watermelon callus induction, MS+1.0 mg/L NAA+2.0 mg/L BA+1.0 mg/L KT and MS+1.0 mg/L NAA+0.5 mg/L BA+2.0 mg/L KT are the most appropriate media for 'YiXuan' and 'JingXin" respectively. However,among 12 media, MS+0.10 mg/L IAA+2.0 mg/L BA+2.0 mg/L KT, is the best for adventitious shoots regeneration from fully dedifferentiated calluses, both for 'YiXuan' and 'JingXin". two types of watermelon.Secondly this paper is focused on the induction of watermelon somaclonal variation that is of enhanced cold tolerance by applying cold stress during in vitro culture. The results indicate that explants treated at 5℃ for 12 days is the proper condition that makes the frequencies of callus induction or direct adventitious shoot regeneration be set at about 50%, called Halflings deadly dosage.Lastly, the results of cold tolerance identification through RT-PCR indicate that, plantlets regeneration after cold stress have the DREB1 gene expression be enhanced intensively in plants either directly or indirectly system from explants that had endured cold treating. However, the gene in control material was not been enhanced after the same low temperature treating, or the enhancement is not visible. The candidate plants for cold tolerance need to be tested on their genetic stability.