Production of haploid and doubled haploid plants of melon (Cucumis melo L.) for use in breeding for multiple virus resistance

We have developed improved procedures for recovery of haploid and doubled haploid (DH) melon plants, using hybrids derived from crosses of lines with multiple virus resistance. Seeds formed after pollination with irradiated pollen were cultured in liquid medium for 10 days before excision of the embryos for further culture. This made it easier to identify the seeds containing parthenogenetic embryos, thereby reducing the effort required and increasing the percentage of plants recovered. The plants obtained (similar to175) were transferred to a greenhouse for evaluation. Three fertile lines were identified, and selfed seeds were obtained for evaluating virus resistance. Flow cytometry of leaf tissues showed that two of these lines were spontaneous DH and the third was a mixoploid containing haploid and diploid cells. The other plants remained sterile through the flowering stage. Flow cytometry of 20 sterile plants showed that all were haploid. Attempts to induce chromosome doubling by applying colchicine to greenhouse-grown plants were unsuccessful. Shoot tips from the haploid plants were used to establish new in vitro cultures. In vitro treatment of 167 micropropagated haploid shoots with colchicine produced 10 diploid plants as well as 100 mixoploid plants. Pollen from male flowers that formed in vitro on the colchicine-treated plants was examined. High percentages of viable pollen that stained with acetocarmine were found not only in the diploids but also in >60% of the plants scored as mixoploid or haploid by flow cytometry. Efficient recovery of DH from hybrid melon lines carrying combinations of important horticultural traits will be a valuable tool for melon breeders.