Induction of parthenogenetic haploid embryos and production of haploid plants in cucumber (Cucumis sativus L.)

Chromosomes number of haploid plants at the sporophyte (2n) stage is equal to the chromosomes number of the gametophyte (n) stage. The objective of haploid plant production is to obtain doubled haploid (DH) lines universally suited to breeding programs. Crop productivity can be greatly improved by using F1 hybrids, which are made by crossing pure lines with some important traits. These pure lines are very valuable in breeding programs and genetic researches. Production of pure lines in a conventional breeding program via self-fertilization takes a long time and requires high costs, but still may not be 100% homozygous. Alternative biotechnological approaches are by far more efficient and sustainable than traditional methods. The most common and best-known method of obtaining haploid cucurbit plants is via pollination with irradiated pollen, which induces parthenogenetic development of haploid embryos in plants. According to the previous reports, there has not been consensus for superiority of gamma ray doses between 300 and 500 Gy; however these two doses have not been simultaneously compared in any research study published so far. The aim of this study was to investigate the possibility of haploid embryos induction in different cucumber cultivars through pollination with gamma-irradiated pollen and determine the optimal dose of irradiation for cucumber haploid plants production. This research study was performed in a factorial experiment with two factors (gamma irradiation dose and plant genotype) based on a completely randomized design (CRD) with 6 replications. In this study the effects of irradiation doses and maternal genotypes on fruit set, seed production, parthenogenetic embryo induction were investigated after pollination by irradiated pollen and production of haploid plants in cucumber. Seven cucumber (Cucumis sativus L.) genotypes including, Extreme F1, Negin F1, Karim F1, Super Dominus F1, Beith Alpha OP, Basmenj and Dasgerdi were pollinated with gamma-rays irradiated pollen grains at doses including 300 and 500 Gy. The pollen viability and pollen tube behavior after irradiation were evaluated. The seeds extracted from the fruits were rescued by in vitro embryo culture, and the ploidy level of the plantlets obtained was determined by flow cytometry. The impact of different doses of gamma irradiation, genotype, and interaction of dose and genotype on total number of seeds produced were significant. The highest number of parthenogenic embryo were observed in genotype Extreme irradiated with dose of 300 Gy (2.25) and genotype Karim irradiated with dose of 500 Gy (1.75). No embryo and plant was obtained in genotypes Negin, Extreme and Beith Alpha irradiated with the dose of 500 Gy. The difference of various doses of irradiation on production of haploid plants was not significant, but genotype and especially interaction effect of dose and genotype were significant on production of haploid plants. Pollination of genotype Extreme by 300 Gy – irradiated pollen grains gave rise to the highest number of haploids (1.25Hs/fruit) produced in this experiment. In this research study similar to previous studies, it was confirmed that production of haploid plants using irradiated pollen grains is an efficient method for producing haploid inbred lines in cucumber. According to our results, different genotypes exhibited different responses to various doses applied and parthenogenic embryogenesis can be induced when optimal dose of irradiation was applied in each genotype.