New Frontiers in Chromosome Elimination-Mediated Doubled Haploidy Breeding for Accelerated and High Precision Genetic Upgradation in Wheat

Conventional plant breeding has been transformed by the chromosome engineers during the last two decades by inventing novel approaches having far reaching implications in accelerating the crop improvement programmes with enhanced precision. Chromosome elimination – a dynamic process occurring during wide hybridization in tetraploid and hexaploid wheats when crossed with various Gramineae genera, has opened new horizon in accelerating the genetic upgradation endeavours in wheat with enhanced precision and efficiency. Since the invention of bulbosum approach, some other potential systems leading to the chromosome elimination viz., wheat x Zea mays  and wheat x Imperata cylindrica have further enhanced the opportunities to increase the doubled haploid production efficiency in wheat. I. cylindrica- mediated approach developed by our group in the year 2005 has emerged as an efficient alternative to the widely used Z. mays – mediated system in terms of natural coincidence for flowering with wheat, abundant pollen supply for longer span, developing significantly higher frequency of doubled haploids from winter and spring wheat ecotypes and even good performance from the triticale x wheat derivatives, where maize-mediated system remained unsuccessful. The I. cylindrica- mediated chromosome elimination approach has further been refined by our group in this Lab by developing certain new and efficient protocols so as to enhance the efficiency of this system to develop very high frequency of doubled haploids in bread wheat. Efforts are afoot in our Lab to explore this innovative tool to induce haploids in other cereals like rice, maize, barley and oat. Although this unique phenomenon of chromosome elimination has opened a gateway to shorten the breeding cycle, accelerate the wheat varietal development programmes and generate gene mapping populations instantly yet acts as a great hurdle during the situation when a breeder desires to introgress targeted genes from the potential pollen sources like Z. mays and I. cylindrica. Hence, it is imperative to resolve the issue related to the genetic mechanism of the chromosome elimination process.  Although we have opined earlier that the chromosome elimination might have occurred due to the lack of kinetochore activity leading to missegregation of chromosomes in mitosis yet there is a dire need to identify the specific genome and the chromosome or specific chromosome arm of wheat responsible for triggering the process of elimination of alien chromosomes during intergeneric hybridization. Our Lab has been making all efforts to resolve this fundamental issue. The resolution of genetic mechanism of the chromosome elimination process can further assist the breeders and geneticists to introgress the desired genes from the targeted species like I. cylindrica associated with high profile drought tolerance and disease resistance especially various rusts and powdery mildew.