Induction Of Cold Tolerant Germplasm In Watermelon By Chemical Mutagenesis In Vitro

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 cold tolerant, and its growing largely be limited seasonally. Therefore, it is urgent to enhance the genetic traits of chilling resistance in watermelon by the ways of combination of chemical mutagen and somaclonal variation.In order to improve the exist breed or create new germplasm, the prior researchers usually use the means of biotechnology, such as meristem culture, protoplast culture, somatic hybridization, gene transformation and somaclonal variation. Currently most of the research on somaclonal variation of watermelon is still focused on direct regeneration system. Only few papers had studied the indirect regeneration system of watermelon, and the system of it is established, the frequency of somaclonal variation improved greatly. But the variety of somaclonal variation in tissue culture is low, and the chance of obtaining useful variation is limited. So in order to increase the variety of somaclonal variation, the chemical mutagen is introduced, the useful variation and mutant with excellent characteristic are selected by using chemical mutagen under certain stress.In this study, we employed the means of combining the use of chemical mutagen and somaclonal variation, induced and selected the chilling resistant mutant in watermelon, and pilot study was conducted on the mutant.Firstly, it focused on establishment of direct regeneration system of watermelon under the treatment of chemical mutagen. The proper condition for both cotyledon extending, adventitious shoots differentiation and half lethal dosage have been determined. And the percentage of germination, the numbers of adventitious shoots and normal seedlings of watermelon is counted. The results showed that the best concentration for inducing chilling resistent mutant in 'YiXuan' is 1.5 mmol/L, which decreased the frequency of explant regeneration to 40.0%, and the adventitious buds per explant to 4.3.Secondly the paper is focused on the physiological mechanism of obtained chilling resistent mutant in watermelon. It established the mechanism of cold tolerance in mutant by determining the factors on chilling resistance under the normal and low temperature. The results indicate that the content of MDA increased slightly, the activity of SOD, POD and CAT enhanced significantly in leaves of regenerate seedlings, which means that the regenerate seedlings' ability of chilling resistent was improved, and the treatment of 1.5 mmol/L NaN3 did the best work.