EFFECTS OF GAMMA-IRRADIATION OF POLLEN ON PARTHENOGENETIC HAPLOID PRODUCTION IN MUSKMELON (CUCUMIS-MELO L)

The effects of increasing gamma ray exposures on muskmelon pollen of t he Vedrantais genotype were evaluated after autofertilization and hybr idization with the Fl.Gl genotype. Regardless of doses of between 0.15 and 1.6 kGy, fruit set and number of seeds per fruit were comparable to those of the control. The pollen tube from pollen irradiated with u p to 2.5 kGy grew in styles and reached the ovules. When pollen was cu ltivated in vitro, relatively high doses of irradiation (1.6 kGy) were needed to reduce the level of germination. Radiation-induced changes in the generative nucleus led to the formation of two chromosomally un balanced sperm cells (as indicated by the appearance of morphological dimorphism) which induced parthenogenetic development of the egg to fo rm a haploid embryo. Haploid embryo production by gamma-irradiated pol len was genotype dependent. For exposures of between 0.15 and 2.5 kGy, the production of embryos was the same, about 3.4%; a maximum of 70% of these embryos placed in a specific culture medium produced haploid plants. The ploidy of the plantlets in vitro was determined by flow cy tometry. No aneuploidy was detected. All resulting plants exhibited no rmal phenotypes.