Chromosome Doubling Methods in Double Haploid and Haploid Inducer-Mediated Genome-Editing System in Major Crops

Abstract

Double haploid technique aims to generate pure inbred lines for basic research and as commercial cultivars. This technique consists in a first obtention of haploid plants and a subsequent chromosome doubling, which can be separated in time or overlapped according to the procedure of each species. Since ever, much effort has been focused on haploid production via androgenesis, gynogenesis or parthenogenesis. Haploid plant obtention is the first step and requires more effort to optimize the haploid plant regeneration, and because of that chromosome doubling had usually been lagged behind. Nevertheless, chromosome doubling has recently been of renewed interest in double haploid research to increase double haploid plant obtention by optimizing and analysing different procedures. New antimitotic compounds, procedures and application methods are being published to ensure the success once haploid material has been regenerated. Moreover, haploid inducer-mediated genome-editing CRISPR/Cas9 system is a new breakthrough method to produce haploid plant material and requires chromosome doubling to succeed. This system could be of great importance for those species with non-successful haploid regeneration methods, or for recalcitrant species. In all cases, the new deployment of this system will demand a suitable chromosome doubling protocol. In this review we run through the existing double haploid and chromosome doubling methods to identify potential opportunities to enhance the breeding process in major crops.