New frontiers in doubled haploidy breeding in wheat

Abstract

Modern agricultural research is focused on the combination of genomes from diverse genetic backgrounds through wide hybridization for sustainable improvement of crop species. Recovery of stable hybrids in certain intergeneric crosses becomes sometimes cumbersome due to preferential uniparental chromosome elimination, a bane for the breeders. This chromosome elimination phenomenon has been turned out into boon through doubled haploidy breeding enabling instant and proficient recovery of haploids and the homozygous recombinants from such crosses in a staple crop like wheat. Many approaches for haploid induction in wheat have been practiced across the world including gametogenic embryogenesis and wide hybridization with distant relatives or wild progenitors. Amongst wide hybridization approaches utilizing chromosome elimination technique in wheat, bulbosum approach took lead but failed due to its genotypic specificity and hence having limited application. Though wheat x maize system, exhibiting genotypic non-specificity, has been utilized for haploidy breeding on large scale but it has failed to produce desirable results in wheat x rye as well as triticale x wheat derivatives. Lately, Imperata cylindrica-mediated chromosome elimination approach has emerged as an highly efficient alternative to the previous approaches for haploid induction in wheat. The invention of this approach has recorded a striking success not only in wheat, but has also succeeded in inducing appreciable number of haploids in wheat x rye and triticale x wheat derivatives as well as in the durum wheat. The novel tools like GISH and FISH of the molecular cytogenetic approach were used to identify, detect and track the elimination of the I. cylindrica chromosomes in wheat x I. cylindrica hybrids at different stages of the mitotic division which enunciated quick elimination of the chromosomes in the first division and attributed to higher recovery of the haploid embryos. The first doubled haploid wheat variety of the country named Him Pratham has been developed and released by utilizing the chromosome elimination approach of doubled haploidy breeding. Many innovative protocols of chromosome elimination approach were further developed for enhancing the haploid induction efficiency manifolds. The present article reviews various haploid induction approaches being undertaken across the globe and assesses them on account of their haploid induction efficiency in wheat.