Induction of parthenogenetic haploid plants using gamma irradiated pollens in 'Hirado Buntan' pummelo (Citrus grandis [L.] Osbeck)

Homozygous genotypes have great potential in breeding and genomic researches in higher plants. Induction of parthenogenesis via pollination with gamma-irradiated pollens is an efficient method to obtain haploid plants that can overcome the biological limitations of fruit trees. In this study, we investigated the induction of haploid plants in 'Hirado Buntan' pummlo (Citrus grandis) through in-situ gynogenesis by pollination with irradiated pollens of trifoliate orange (255, 325 and 500 Gy) and 'Tongshui 72-1 Jincheng' sweet orange (255, 395 and 500 Gy). The pollen stainability, pollen tube behavior after pollination were evaluated. The seeds extracted from the fruits were rescued by in vitro embryo culture, and the ploidy level of the obtained plantlets was determined by flow cytometry. It showed that two haploid plants and one triploid plant, were obtained from the cross-pollination of 'Hirado Buntan' pummelo with irradiated pollens of trifoliate orange; two haploid plants were obtained from the cross-pollination of 'Hirado Buntan' pummlo with irradiated pollens of 'Tongshui 72-1 Jincheng' sweet orange. The parthenogenic origin of the haploid plants was further confirmed by chromosomal cytogenetic and SSR analysis. The 'Hirado Buntan' haploid plants obtained here hold great potential in citrus genetic and genomic studies in the future.