Review of research on haploid production in cucumber and other cucurbits

This review provides a summary of haploid induction methods and factors affecting the efficacy of specific methodologies as applied to cucumber (Cucumis sativus L.), melon (Cucumis melo L.), watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai), winter squash (Cucurbita maxima Duch. ex Lam.), summer squash (Cucurbita pepo L.) and other cucurbits. This report is focused on studies that were carried out during the last 20 years.

The main objective of the research on the production of haploid cucurbit plants is to accelerate breeding programs through the use of homozygous double haploid lines (DHL) and to facilitate the selection of desired (e.g. disease-resistant) genotypes for breeding. Unfortunately, currently used protocols result in a low number of double haploids (DH). 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 planta. The embryos are extracted from immature seeds and cultured in vitro to facilitate the maturation and development of plants. The studies described below were primarily aimed at the determination of an appropriate dose of radiation and the evaluation of the impact of the genotype and the time of year on the number of haploid embryos and plants obtained.

A less popular method of haploid production - ovule and ovary culture - is based on in vitro gynogenesis. The studies related to this method concentrated on optimising the composition of the medium and pre-treatment conditions (primarily temperature) to which the flower buds were subjected.

Recently, increasing attention has been paid to anther and microspore culture. As in the case of in vitro ovule and ovary culture, the medium composition and flower bud pre-treatment conditions were optimised. The most recent studies suggest that anther culture is comparable in effectiveness to the irradiated pollen technique.