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CELL BIOLOGY & MOLECULAR GENETICS

Seedset on Synthetic Haploids of Durum Wheat

Cytological and Molecular Investigations

^a USDA-ARS, Northern Crop Science Lab., Fargo, ND 58105 USA
^b Dep. of Botany, Faculty of Sciences, Univ. of Aleppo, P.O. Box 12252, Aleppo, Syria

pjauhar{at}badlands.nodak.edu

Because of their great importance as cytogenetic and breeding tools, haploids have been produced in several crop plants, including wheat (Triticum aestivum L.). Reports of seedset on haploid plants are very rare. Earlier, we produced 142 haploids (2n = 2x = 14; AB genomes) of seven commercial durum wheat (Triticum turgidum L.) cultivars (Cappelli, Durox, Langdon, Lloyd, Medora, Monroe, and Renville) by crossing them with maize (Zea mays L.). Of these, we studied 101 haploids. Some haploids from each of the cultivars set seed without colchicine treatment or cross pollination. The cytological basis of this interesting phenomenon was studied. Because all cultivars have the homoeologous pairing suppresser Ph1, their haploids formed mostly univalents and had irregular meiosis. Yet, viable seed was formed on some haploids. The seedset varied with the genotype. Langdon, with a mean of 2.75 seeds per haploid, was the highest yielder. These seeds gave rise to normal disomic (2n = 4x = 28; AABB) plants. The seeds had viable embryos formed by fusion of unreduced male and female gametes with 14 chromosomes each. The unreduced gametes were formed by two closely related first division restitution mechanisms resulting in meiotic non-reduction: (i) complete failure of movement of univalents at anaphase I, followed by normal second (equational) division, and (ii) anaphase I movement of all univalents to one pole. Thus, formation of these gametes bypassed the reductional division but occurred by normal equational division. It is hypothesized that lack of pairing may be a prerequisite for the occurrence of meiotic restitution and hence chromosome doubling. Fluorescent GISH (genomic in situ hybridization) analyses of somatic and meiotic chromosomes of the haploid-derived plants showed the complete duplication of both the A- and B-genome chromosomes. Fertility of the derived disomics and the presence of two doses of the marker chromosome involving the 4A·7B translocation, an evolutionary landmark of durum wheat, further corroborated the precise duplication of all chromosomes. We found that the distal segment translocated from chromosome 7B constitutes approximately 24% of the long arm of 4A.

Abbreviations: DH, doubled haploid • FDR, first division restitution • FISH, fluorescent in situ hybridization • FITC, fluorescein isothiocyanate • GISH, genomic in situ hybridization • PI, propidium iodide • PMCs, pollen mother cells • SDR, second division restitution

This article has been cited by other articles:

				P. P. Jauhar Meiotic Restitution in Wheat Polyhaploids (Amphihaploids): A Potent Evolutionary Force J. Hered., April 11, 2007; (2007) esm011v2. [Abstract] [Full Text] [PDF]

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