| Melon(Cucumis melo L.), also known as muskmelon, belongs to Cucurbitaceae and is one of the important fruit vegetables widely grown all over the world. Recent years, in terms of melon breeding, issues of narrow genetic basis and fragile ability resist abiotic and biotic stresses in melon have limited the yield and quality improvement of melon. However the main goal for the melon breeders is to develop high yield and quality melon varieties. Germplasm resource with rich genetic background proves to be very important in melon breeding and relevant biological research.Innovation of germplasm resource has an great importance in cultivating melon varieties with high yield and high quality. With the accomplishment of melon genome sequencing in 2012, it has provided massive molecular data and genetic basis. Research in melon has been in post-genomic era. The most powerful approach to isolate and identify gene functions in melon is to construct melon mutant library rich in genetic variation.Ethyl methane sulfonate(EMS) has been extensively used as a chemical mutagen that results in high-point mutational densities and performs random mutagenesis of a whole organism.Therefore, it was widely used in crop breeding and plant functional genomics research. However,there is hardly any report on the effect of EMS in melon.In our study, seeds of a melon strain, ‘3-2-2’, were treated by different EMS concentration of0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4% and 1.6% for 12 h, 24 h, 36 h and 48 h. We determined 24 h,1.2% EMS as the appropriate mutagenic dosage in this experiment for ‘3-2-2’, Through which we constructed a melon mutant library which was rich in phenotypic variation.In this mutant library, there existed different phenotypic variation in various organs in M1 generation. The total rate of phenotypic variation was up to 71.53%.In this mutant library, 6 phenotypic traits, that is, length of internode, diameter of main stem,length of leaf, width of leaf, length of petiole and diameter of petiole, were investigated in M2 generation. In addition to internode length, differences of the other 5 traits were significant compared to the wild type(P < 0.05); variation coefficient in different phenotypic traits were different, the maximum was up to 15.37% in length of petiole, and the minimum was 7.10% in length of internode. variation coefficient in length of petiole was significant different to other 5traits, indicating that genetic scope was wide and selection potential in length of petiole was abundant in our melon mutant library. The result in preliminary genetic analysis of M2 generationshowed that 19 SNPs in 10 lines out of 67 lines were detected and they were respectively located in chromesome 1, 2, 3, 4, 5, 6, 8 and 11.The result in preliminary physiological and biochemical identification of No.25 line xantha mutant in M2 generation showed that the trait of yellow leaf of this melon xantha mutant which belonged to total chlorophyΙΙ deficiency type was appeared from cotyledon period, kept stable maintainance in vigorous growth stage and transformated green color which was roughly same to the wild type. The structure of chloroplast in this xantha mutant was hypoplasia, the content of photosynthetic pigments was decreased, but photosynthetic rate was increased. |
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