The Research Of Cold Tolerant In Watermelon Seedlings Stage

Watermelon origins from the Africa and is typical thermophilic fruits. Watermelon oftensuffer a long period disastrous weather of low temperature and weak light during theoff-season with the solar greenhouse and early spring canopy of cultivation of watermelonarea is bigger and bigger, which lead to serious impact on the growth and development of theseedlings and yield and quality. Therefore, study of cold tolerance in watermelon seedlingsand the change of the physiological and biochemical characteristics and the selection of coldtolerance materials of watermelon seedlings under low temperature and weak light hasimportant instruction meaning for breeding of strong seedling and increasing of the yield andquality of watermelon.In this experiment, watermelon seedlings were used as the experimental material to studythe identification of cold tolerant physiological change and the selection of chilling tolerantcultivars. The results were as follows:1. Six different genotypes of watermelon seedlings were used as the experimentalmaterial, under different low temperature treatments, cold tolerance of watermelon seedlingswas studied. The result showed that different genotypes watermelon represent significantdifference at10℃,light100μmol·m-2·s-1and treatment after12days, the identification method ofwatermelon seedlings cold tolerance was preliminary build up and cold tolerant germplasm'M08' and cold sensitive germplasm 'Liaoyin No.1' was selected.2. In order to compare the difference of leaf anatomical structure, the cold resistantvarieties and cold sensitive varieties of watermelon seedlings' leaves were used as theexperimental materials to make the paraffin section. The results showed that the two varietiestreated with low temperature and weak light stress, their palisade tissue, sponge tissue, leafthickness and thickness ratio between palisade tissue and spongy tissue decreased beforetreatment; And palisade tissue and sponge tissue are getting looser, and the intercellular spaceare bigger; Cold resistant varieties of watermelon seedlings palisade tissue, sponge tissue, leafthickness, and thickness ratio between palisade tissue and spongy tissue are greater than coldsensitive watermelon varieties.3. The selected cold resistant varieties and cold sensitive varieties of watermelon seedlings' leave were treated at the age of three leaves with spraying brassinolide with thedifferent concentration of0(CK),0.01,0.05,0.1,0.5, and1mg.L-1. The change ofphysiological and biochemical indexes of watermelon seedlings' leaves were studied after0,2d,4d,6d,8d and10d under low temperature in low light. The results indicated that thebest seedlings growth was under the treatment of BR0.1mg.L-1, which can reduce thechilling injury index significantly, increase the activities of superoxide dismutase (SOD),peroxidase (POD) and catalase (CAT) and reduce the content of malondialdehyde (MDA).4.46watermelon germplasm resources of cold tolerance level were preliminary screenedaccording to the identification method of watermelon seedlings stage cold tolerance. Throughtesting46watermelon seedlings chilling of index under low temperature and weak light at2d,4d,6d,8d,10d and12d and using SAS software processing,5watermelon cold tolerancematerial were screened, provides an important material basis for the breeding afterward.