Submitted to: Euphytica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/8/2003
Publication Date: 8/1/2003
Citation: JAUHAR, P.P. FORMATION OF 2N GAMETES IN DURUM WHEAT HAPLOIDS: SEXUAL POLYPLOIDIZATION. EUPHYTICA. 2003. V. 133. p. 81-94. Interpretive Summary: Hybridization between wild species, accompanied or followed by chromosome doubling, played a very important role in the evolution of many of our important grain, forage, and fiber crops. These polyploid crop plants (with several sets of chromosomes) have developed a regulatory mechanism that controls chromosome pairing in such a way that only identical partners pair even though there are several sets of chromosomes. This regulation of chromosome pairing brings about reproductive stability to polyploid crop plants, which enjoy the benefits of hybridity and polyploidy. Sexual reproduction is also important to create genetic diversity. We present evidence for the occurrence of sexual polyploidization in durum haploids (plants with half the chromosome number) and discuss the evolutionary and breeding significance of this phenomenon. It is concluded that three factors, sexual reproduction, polyploidy, and genetic control of chromosome pairing, jointly constitute a perfect recipe for rapid evolution in nature.
Technical 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 today. The allopolyploid species, for example, 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 FDR nuclei and 2n gametes. The evolutionary and breeding significance of sexual polyploidization is discussed. It is emphasized that three factors, viz., sexuality, allopolyploidy, and genetic control of chromosome pairing, jointly constitute a perfect recipe for cataclysmic evolution in nature.