Induction of polyploidy in cucumis melo ‘chammel’ and evaluation of morphological and cytogenetic changes

This study explored the effects of oryzalin on the polyploidization of a new cultivar, Cucumis melo ‘Chammel’. 58 diploid seedlings of ‘Chammel’ were treated with oryzalin. Their ploidy levels were checked by flow cytometry and number of 5S and 18S rDNA loci were examined by fluorescence in situ hybridization (FISH). Twelve among 58 plants were identified as tetraploids. The tetraploids were self-crossed, and their seeds were harvested. The seeds and seedlings of the tetraploids were compared to the corresponding diploids using morphology and cytogenetic analyses. The seed width, the cotyledon width, and the leaf thickness of the tetraploids increased significantly over those of the diploids. However, the length of the petiole of the tetraploids was shorter than that of the corresponding diploids. The stomata length and width of the guard cells in the tetraploids were longer than in diploids, but the number of stomata per area decreased in the tetraploids. The number of chromosomes was 24 and 48 for the diploids and tetraploids, respectively. Moreover, the chromosomal changes induced by oryzalin were confirmed; the diploids had one pair of 5S rDNA loci and two pairs of 18S rDNA loci, the corresponding numbers were doubled in the tetraploids. These results will help to generate new seedless oriental melon cultivars via polyploidization.