Formation of 2n gametes in durum wheat haploids: Sexual polyploidization

Abstract

Allopolyploidy, resulting from interspecific and intergeneric hybridization accompanied by sexual doubling of chromosomes, has played a major role in the evolution of crop plants that sustain humankind. The allopolyploid species, including durum wheat, bread wheat, and oat, have developed a genetic control of chromosome pairing that confers on them meiotic regularity (diploid-like chromosome pairing), and hence reproductive stability, and disomic inheritance. Being natural hybrids, they enjoy the benefits of hybridity as well as polyploidy that make them highly adaptable to diverse environments. Despite the complexities of sexual reproduction, it is widespread among plants and animals. Sexual polyploids are highly successful in nature. Sexual polyploidization is far more efficient than somatic chromosome doubling. Sexual polyploidization effected by functioning of unreduced (2n) gametes in the parental species or in their hybrids has been instrumental in producing our grain, fiber, and oilseed crops. Evidence is presented for the occurrence of sexual polyploidization in durum haploids. The Ph1-induced failure of homoeologous pairing is an important factor in the formation of first division restitution (FDR) nuclei and 2n gametes. The evolutionary and breeding significance of sexual polyploidization is discussed. It is emphasized that three factors, viz., sexual reproduction, allopolyploidy, and genetic control of chromosome pairing, jointly constitute a perfect recipe for cataclysmic evolution in nature.