Parthenogenetic double haploid production in melon 'Piel de Sapo' for breeding purposes

Abstract

Double haploids in melon breeding are commonly used for hybrid F1 production. Via parthenogenesis, double haploids can be efficiently obtained in melon. Melon fruit traits and pathogen resistances were first appraised to analyse the commercial value of donor genotypes further used in a parthenogenetic process. Parthenogenetic capacity from melon 'Piel de Sapo' germplasm, including six inbred genotypes and Melito cultivar, was evaluated and optimized in this study. Melon fruit set after pollination with irradiated pollen, haploid embryo obtention, in vitro germination and growth of haploid embryos, in vitro and in vivo chromosome doubling with colchicine or oryzalin, and fruit set of double haploid plants were steps deeply assessed in this study. Parthenogenetic efficiencies of 'Piel de Sapo' genotypes showed a high genotypic dependency during the whole process. Pollinated female flowers set fruit after pollination with irradiated pollen (15.78%). Three different methods were assayed for haploid embryo detection of the 178 melon fruits recovered: one-by-one, X-ray and liquid medium. X-ray radiography of seeds was 4-5 times faster than one-by-one method and jeopardized eight times less haploid embryo obtention than liquid medium. One third of those fruits carried haploid embryos, which 50.94% did not developed into plantlets because failed to germinate or plant died at the first stages of development as a consequence of deleterious gene combination in haploid homozygosity. The distribution of the ploidy-level of 26 parthenogenetic plantlets was: 73.08% haploids, 23.08% spontaneous double haploids and 3.84% mixoploids. Two in vitro chromosome doubling methods with colchicine or oryzalin were compared with a third in vivo method. In vivo immersion of apical meristems showed the best results of plant survival, 57.33%, and doubling, 9.30% mixoploids and 20.93% double haploids. Fruit set and seed recovery of double haploids plants was achieved. In this study, double haploid lines were produced from the seven genotypes of melon 'Piel de Sapo', however, further improvements are needed to increase the parthenogenetic efficiency.