Abstract
Homozygous dihaploid lines (DHLs) from new cucumber (Cucumis sativus L.) accessions, source of resistance to diseases, would be useful to accelerate breeding for new resistant varieties. DHLs have been generated by in vitro rescue of in vivo induced parthenogenic embryos. The protocol developed involves the following: 1) induction of parthenogenic embryos by pollination with pollen irradiated at 0.5 KGy with a Co 60 γ-ray source; 2) in vitro rescue of putative parthenogenic embryos identified by their morphology and localized under a dissecting scope or X-ray radiography; 3) discrimination of undesirable zygotic individuals from the homozygous plants using cucumber and melon SSR markers; 4) determination of ploidy level from homozygous plants by flow cytometry; 5) in vitro chromosome doubling of haploids; and 6) acclimation and selfing of lines. Codominant markers and flow cytometry confirmed the gametophytic origin of plants regenerated by parthenogenesis, since all homozygous lines were haploids. No spontaneous doubled haploid plants were rescued. Chromosome doubling of haploid plants was accomplished by an in vitro treatment with 500 μM colchicine. Rescue of diploid or chimerical plants was confirmed by flow cytometry, previous to their acclimation and plant growth in the greenhouse. Selfing of colchicine-treated haploid plants allowed the perpetuation by seed of homozygous lines. Seeds were harvested from almost all lines after selfing in the greenhouse. The high rate of seed production facilitated the recovery of inbred lines. Despite some limiting factors, parthenogenesis is routinely used in a cucumber-breeding program to achieve complete homozygosity in one generation, and accelerate breeding for new commercial varieties. DHLs have been used as parental lines for the production of commercial hybrids.
Published Version
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