Cucurbit Genetics Cooperative Report 12:22-23 (article
Haploid Gynogenesis in Cucumis sativus Induced by Irradiated Pollen
Royal Sluis France, Research and Development Station, BP 1431 30017 Nimes, France
A very efficient method of doubled haploid production is now commonly used in muskmelon (Cucumis melo L.) breeding programs (2). This method consists of the induction of gynogenesis in situ with gamma-ray irradiated pollen, then followed by rescue of haploid embryos by in vitro culture.
My first attempts to apply the same method in cucumber (minicucumber type) were promising and produced viable gynogenetic haploid plants. (1). this study was undertaken in order to develop the method for cucumber.
The gynogenetic induction and development process is similar in muskmelon and cucumber. In the two cases, when an irradiation from 300 to 1000 Gy was applied, the pollination with such irradiated pollen induced normal development of fruit and seed coats. In one fruit, only a small number of seeds were not empty. Three weeks after pollination with irradiated pollen, these seeds contained either a single embryo, which was haploid, or an undifferentiated structure that was probably a pseudo-endosperm or an aborted embryo. Embryo and endosperm were never observed together in the same seed. Some haploid embryos had reached the cotyledon stage, while other embryos were less differentiated (globular, heart shaped, or torpedo stage).
In cucumber, a great variation in the rate of gynogenetic induction was recorded among fruits. This heterogeneity was observed regardless of genotype studied (minicucumber type with different levels of parthenocarpy). The mean rate of viable plants was about 3 per 1000 seeds if all the developed seeds produced in fruits after pollination with irradiated pollen were taken into account. However, after pollination with normal pollen in the minicucumber type under our culture conditions, only 30 to 60% of seeds were full. Therefore, for each genotype, the real rate of viable gynogenetic plants might be calculated according to the mean number of ovules susceptible to be fertilized. This rate in the minicucumber type was near 1%.
Cucumber haploid plants were propagated in vitro by successive microrootings. Spontaneous diploidization was frequent in root meristems especially when plants had undergone several cycles of microrooting. These plants grew rapidly and normally in soil and produced staminate and pistillate flowers which were generally smaller than diploid ones. Furthermore, their petals were not joined together at the corolla base. The plants remained haploid and produced pollen grains typical of haploid plants. Chromosome doubling was obtained by colchicine treatment of haploid cuttings in vitro. Doubled haploid plants produced normal and fertile pollen and normal seeds.
Further studies are in progress to i) increase the production of viable haploid plants, ii) apply the soft X-ray radiography technique to detect haploid embryos in immature seeds as it has been shown in melon (3), and iii) perform the technique of chromosome doubling.
- Andre, I. 1988. In vitro haploid plants derived from pollination by irradiated pollen on cucumber. Proceedings of the Eucarpia meeting on Cucurbit Genetics and Breeding, Avignon - Montfavet, France. 31 May, 19888, 06/01-02, 143-144.
- Sauton, A. 1988. Doubled haploid production in melon (Cucumis melo L). Proceedings of the Eucarpia meeting on cucurbit genetics and breeding, Avignon - Montfavet, France. 31 May, 1988, 06/01-02, 119-128.
- Sauton, A., C. Olivier and A. Chavagnat. 1988. Use of soft X-ray technique to detect haploid embryos in immature seeds of melon. ISHS 4th International Symposium on Seed Research in Horticulture. Angers, France. 5-9 Sept., 1988, Acta Hort. (in press).