Study On Tetraploid Induction Of Mini-watermelon And Fruit Characteristics And The Embryo Development Of The Different Ploidy

Through field dropping seedling, nine diploid mini-watermelon inbred lines were treated by herbicide Oryzalin. The mutants were identified through analyses of morphology, cytology and chromosome counting. The major agronomic characteristics of the different ploidy inini-watermelon fruits were determinated, and the embryonic development of the different ploidy mini-watermelon were studied, to explore the impact of ploidy changes on watermelon quality and sterility, and to improve methods of fertility or seed yield of tetraploid mini-watermelon. The results indicated:1. Induction and identification of tetraploid mini-watermelonThe different varieties had different variation frequencies, using the treatment method of field dropping seedling by using herbicide40mg/L Oryzalin as mutagen. The method of chromosome counting for ploidy determination, the highest variation frequency was line qing123, up to23.1%, the lowest variation frequency was line032, only5.9%, and the average variation frequency was11.9%.Through evaluation of chromosome counting, the accessions Qing123and032had the highest and the lowest variation frequency of23.1%and5.9%, respectively.There were extremely significant differences between tetraploid and homologous diploid in field morphological characteristics, including the first male flowering node, stem length of seedlings growth stages, leaf width and leaf shape index, petal length and width, the diameters of anthers and pedicels, peel thickness and fruit shape index, seed width and thickness; These morphological characteristics can be used as the standards of field morphological identification, with the accuracy of74.3%.In cytological characteristics, there were extremely significant differences between tetraploid and homologous diploid in the pollen grain size, stomatal density, guard cell length, and chloroplast number in guard cells; these characteristics can be used as the standards of ploidy identification.Based the chloroplast number in guard cells, the accuracy of ploidy identification was90.2%. Thus, using the numbers of chloroplasts in guard cells for ploidy level identification was highly accurate and simple.2Determination of the major agronomic characteristics of the different ploidy mini-watermelonsThere were significant differences between different ploidy mini-watermelon fruits in the lycopene, citrulline, vitamin C (Vc), centrer total soluble solids (TSS) content, and the contents of these components was higher in tetraploid than in homologous diploid.There were significant differences between the same ploidy and the different flesh color mini-watermelon fruits in the lycopene, citrulline and Vc. The results indicated that, lycopene content:bright red flesh> red flesh> pink flesh> yellow flesh; citrulline content:yellow flesh> bright red flesh=red flesh> pink flesh; Vc content:yellow flesh> bright red flesh> pink flesh> red flesh. Center TSS content: bright red flesh> other flesh colors, There were no significant differences in center TSS content of other flesh colors.3. The embryonic development and fertility of tetraploid mini-watermelonThe morphology of diploid pollen was regular and the germination rate was high, up to96.3%; and the growth rate of pollen tube was high, after9hours they can enter the ovary; The morphology of tetraploid pollen was abnormal and the germination rate was low to63.7%with thepollen tube twisted, folded, coiled, and poor growth, after for12h they could reach the ovary. Tetraploid pollen and pollen tube abnormalities were one of the reasons for the low fertility of tetraploid watermelons.The embryonic development of diploid was fast with little degradation. The embryonic development of tetraploid was slow, from ball embryo to torpedo embryo, the disintegration of the endosperm cells can result in the degradation of embryo, which was one of the important reasons for the low fertility of tetraploid watermelons.Using diploid watermelon varieties with high fruit-set and the number of seeds for inducing could improve the seed yield. Continuous self-pollinated could also increase fertility of the tetraploid mini-watermelon.