Studies On The Polyploid Watermelon Induction And The Foundations Of Molecular Biology

Watermelon (Citrullus lanatus), originating in the Africa, is a world horticultural crop.The fruit of watermelon is crisp, sweet and juicy. Because of its high mineral salts andvitamins content, it is considered to be rich in nutritional value. With the development ofliving standards recently, people has more requirements for the quality of watermelon. In1939, Kihara obtained the first tetraploid watermelon successfully by using colchicine asmutagen. from then on, polyploid breeding of watermelon moved into a new era, whichwas developed extensively in the whole world. Lots of polyploid watermelon varietieswere cultivated and popularized rapidly. Compared with the brilliance achievements ofproduction practice, theoretical research of polyploid watermelon is lagging, which mainlyfocuses on morphological variations and cytology variations. While the research atmolecule level is less reported. In this study, the inbred line of diploid watermelon(ZJM)was used as experiment material, whose chromosome was doubled finally. Triploidwatermelon was obtained by crossing tetraploid watermelon and polyploid watermelon;Differential expression of genes in the process of chromosome doubling were analyzedwith cDNA-SCoT technique. Genes related to chromosome doubling were analyzed. AFLPmolecular marker was used to study the relationship between phenotype and genotype indifferent ploid watermelons；MSAP analysis was carried out to analyze the methylationlevel and methylation status.1.The inbred line of diploid watermelon(ZJM) was used for experiment material.autotetraploid was induced successfully by using herbicide Oryzalin as mutagen. weestablished methods of polyploidy identification throughout the whole growing period.2.Homologous triploid watermelon was derived from crossing ZJM(4x)and ZJM(2x),moreover, seedless watermelon was also obtained.3.cDNA-SCoT technique was used to analyze differential expression of genes in theprocess of chromosome doubling. Gene fragments which were related to chromosomedoubling were obtained. Stable appeared fragments were sorted out, cloned and sequenced.The results indicated that their biological functions related mainly to cell division, energyand metabolism, protein processing and degradation, transmembrane transport and stressresistance.4.AFLP molecular marker was carried out to analyze the DNA of different ploidwatermelons. The results indicated that there was no change of DNA among3different ploidy watermelons.The desirable traits of experiment material retain well.5. MSAP technique was used to analyse the DNA of different ploidy watermelons. Theresults showed that the methylation exist in the3different ploid watermelons whichchanged after chromosome doubling and crossing. The total methylation ratio in3differentploid watermelons are about25.2%、28.5%、28.2%. The diversity of methylation is notnotable. The methylation status of the3different ploidy watermelons are all based on fullmethylation, the ratios are24.9%、22.5%、21.9%.The ratios of hemimethylation in3different ploid watermelons are low, the number are2.7%、3.6%、6.3%, which arepositively correlated with the ploidy of watermelons. Compared with diploid watermelon,there are a few of adjustments in DNA methylation pattern.6.9%of methylation sites intriploid watermelon and8.5%of methylation sites in tetriploid watermelon arehypermethylated;3.3%of methylation sites in triploid watermelon and3.0%ofmethylation sites in tetriploid watermelon are demethylated. These changes may be relatedto polyploidization and hybridization which result in genome impact. Recovery balance ofnucleo-cytoplasmic is also closely related to the changes.