Protoplast regeneration and fusion in Cucumis: Melon x cucumber

The aim of this investigation was to develop a protocol to be used in asymmetric protoplast fusions with breeding material of melon and cucumber. Efficient methods for plant regeneration from unfused protoplasts of commercial melon lines were established and are reported. Ploidy levels of explant material and plants, regenerated from protoplasts were analyzed. Electrofusion was carried out between melon protoplasts and irradiated and non-irradiated donor protoplasts of cucumber. Although initial plating efficiencies of heterokaryons were high, development stopped after a few divisions. In control experiments, shoots were regenerated at high frequencies. In only two fusion experiments, development continued to the callus stage, but further development was not observed. When analyzed with PCR using arbitrary primers, the majority of these calli DNA were identical to the melon DNA. However, a few of the examined calli, although being mainly homologous to melon, were observed to have new bands corresponding to bands specific for cucumber. Due to sexual incompatibility, successful hybridization between cucumber and melon was never obtained by sexual crosses. We suggest that the failure to regenerate plants in our fused material could be explained partially by an analogous somatic incompatibility reaction.