ARS | Publication request: SPONTANEOUS HAPLOIDS IN DURUM WHEAT: THEIR CYTOGENETIC CHARACTERIZATION

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2005
Publication Date: April 10, 2006
Citation: Jauhar, P.P. 2006. Spontaneous haploids in durum wheat: their cytogenetic characterization. Euphytica 148:341-344.

Interpretive Summary: Durum wheat, also called macaroni wheat, arose in nature as a hybrid between two wild progenitor species. The two progenitors, each with 14 chromosomes, hybridized in nature about half a million years ago and gave rise to tetraploid wheat with 28 chromosomes as a result of chromosome doubling their hybrid. It is easily possible to recreate this step under laboratory conditions and obtain durum haploids with half the chromosome number, i.e., 14 chromosomes, and then regenerate from them normal durum plants with 28 chromosomes. Interestingly, such a reversion to haploidy, or half the chromosome number, does occur in nature as well, although at a very low frequency. This article reports on the occurrence of two spontaneous durum haploids in our greenhouses and describes their chromosomal characteristics. The haploids had 14 chromosomes, which after a specialized staining technique, called fluorescent genomic in situ hybridization (fl-GISH), could be distinguished as 7 A-genome and 7 B-genome chromosomes, contributed by each of the two wild progenitors. This is one of the very few reports of the occurrence of spontaneous haploids in durum wheat.

Technical Abstract: Durum or macaroni wheat (Triticum turgidum L., 2n = 4x = 28; AABB genomes) arose as a natural hybrid between two wild species, Aegilops speltoides Tausch (2n = 2x = 14; BB genome) and Triticum urartu Tumanian (2n = 2x = 14; AA genome). The two progenitors hybridized in nature about half a million years ago and gave rise to tetraploid wheat, presumably in one step as a result of functioning of unreduced gametes in their hybrid BA (amphihaploid). It is easily possible to go back on the evolutionary scale and obtain durum haploids BA, and then regenerate from them tetraploid durum plants. Interestingly, such a reversion to haploidy does occur in nature as well, although at a very low frequency. This article reports on the occurrence of two spontaneous durum haploids in our greenhouse and describes their chromosomal characteristics. The haploids had 14 somatic chromosomes, which on fluorescent genomic in situ hybridization (fl-GISH), could be distinguished as 7 A-genome and 7 B-genome chromosomes. At meiosis, only 2.3 and 2.7 % of the chromosomes paired in the two haploids, because of the presence of the homoeologous pairing-suppressor gene, Ph1. This is one of the very few reports of spontaneous haploidy in durum wheat.