Mohammad Sadat-Hosseini

We report the first successful regeneration of haploid lines in persian walnut (Juglans regia) developed byin situ parthenogenesis followed by embryo rescue. Female flowers of cultivars Hartley and Pedro and two nativeIranian selections (Z63and Z67) were pollinated using pollen of selections Z53and Z30that had been irradiated withgamma rays at five doses (50, 150, 300, 600, and 900 Gy). Gamma-irradiated pollen induced fruit set and developmentof some parthenogenetic embryos. The immature embryos were excised 30 and 45 days after pollination, cultured invitro, and then stratified for 30 days at 48C to overcome dormancy. Ploidy level of the resulting plantlets wasdetermined by chromosome counting and flow cytometry. Haploid plants were obtained from ‘Hartley’, ‘Pedro’, Z63,and Z67after pollination using pollen irradiated at 300 and 600 Gy. Plants obtained from pollen irradiated at 50 and150 Gy were all diploid. Molecular marker analysis using four simple sequence repeat (SSR) markers also showed thatall the diploid plants recovered were zygotic and no spontaneous double haploid plants were obtained in this work.Also, the haploid plantlets presented only one alleleof their female parents. These profiles confirmed theparthenogenetic origin of the obtained haploid plants. The techniques used to induce haploid walnut plants byirradiated pollen were successful and could be used in breeding programs and accelerate genome analysis in this plantin which the genome size is approximately three times the size of the human genome.