Abstract
Doubled haploids have played a major role in cucurbit breeding for the past four decades. In situ parthenogenesis via irradiated pollen is the preferred technique to obtain haploid plantlets whose chromosomes are then doubled in Cucurbitaceae, such as melon, cucumber, pumpkin, squash and winter squash. In contrast to doubled haploid procedures in other species, in situ parthenogenesis in cucurbits presents many limiting factors which impede efficient production of haploids. In addition, it is very time-consuming and labor-intensive. However, the haploid inducer-mediated genome-editing system is a breakthrough technology for producing doubled haploids. Several reports have described using the CRISPR/Cas9 system in cucurbit species, and although its application has many bottlenecks, the targeted knock-out of the CENH3 gene will allow breeders to obtain haploid inducer lines that can be used to obtain parthenogenetic embryos. In this review, we discuss the progress made towards the development of doubled haploids and haploid inducer genotypes using CRISPR/Cas9 technologies in cucurbit species. The present review provides insights for the application of haploid inducer-mediated genome-editing system in cucurbit species
Highlights
The Cucurbitaceae is a family with several important crop species and contains a great genetic, morphologic and phenotypic variability
Parthenogenic doubled haploid (DH) methodology in cucurbits consists of two basic steps, the initial production of haploid material through in situ parthenogenesis via pollination with irradiated pollen and the subsequent chromosome doubling of haploid plants to restore the diploid chromosome content and to allow the generation of DH seed
The purpose of this review is to focus on haploid inducer-mediated genome-editing systems in cucurbit species to provide new insights, opportunities and challenges, which may be valuable for developing this technique in cucurbits and other species
Summary
The Cucurbitaceae is a family with several important crop species and contains a great genetic, morphologic and phenotypic variability. There are two main methods in cucurbits to produce completely homozygous lines, classical breeding and doubled haploids. On the other hand, doubled haploid (DH) methodology allows the efficient production of completely homozygous pure lines in less than two years. Parthenogenic DH methodology in cucurbits consists of two basic steps, the initial production of haploid material through in situ parthenogenesis via pollination with irradiated pollen and the subsequent chromosome doubling of haploid plants to restore the diploid chromosome content and to allow the generation of DH seed. The haploid inducer-mediated genome-editing system is a breakthrough approach that could lead to a new era of cucurbit breeding. The purpose of this review is to focus on haploid inducer-mediated genome-editing systems in cucurbit species to provide new insights, opportunities and challenges, which may be valuable for developing this technique in cucurbits and other species
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