Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/2000
Publication Date: 11/15/2000
Citation: Jauhar, P.P., Altuntepe, M., Peterson, T.S., Almouslem, A.B. 2000. Seedset on synthetic haploids of durum wheat: cytological and molecular investigations. Crop Science 40:1742-1749. Interpretive Summary: Durum wheat has 28 chromosomes (rod-like structures that carry genes for various traits) in each of its cells. We produced, in 1997, 142 haploids (plants with half the chromosome number) of seven commercial durum wheat cultivars (Cappelli, Durox, Langdon, Lloyd, Medora, Monroe, and Renville) by crossing them with maize. Of these we studied 101 haploids with the Ph1 gene, which suppresses pairing between less related chromosomes. As expected all 101 haploids had mostly 14 univalents (unpaired chromosomes). Generally, such haploids are completely sterile. However, some of our durum haploids from each cultivar produced seed. Using cytological and molecular techniques we investigated the causes of seedset on our haploids. They formed 14 univalents, which divided into 28 chromatids (half chromosomes) at the first division of meiosis (cell division in the reproductive organs) but remained in the same cell. Under normal circumstances the chromosome number is halved at the first cell division. At the second division, 14 chromatids went to each pole and thus formed unreduced gametes. These gametes gave rise to normal embryos and then seeds. The production of normal, viable seed on haploids led to the production of disomic (normal) homozygous (genetically pure) durum plants. Haploid-derived homozygous lines are important for basic studies in genetics and they help accelerate breeding work.
Technical Abstract: Because of their great importance as cytogenetic and breeding tools, haploids have been produced in several crop plants, including wheat. Reports of seedset on haploid plants are very rare. We produced, earlier, 142 haploids (2n = 2x = 14; AB genomes) of seven commercial durum wheat cultivars (Cappelli, Durox, Langdon, Lloyd, Medora, Monroe, and Renville) by crossing them with maize. 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: a) complete failure of movement of univalents at anaphase I, followed by normal second (equational) division, and b) anaphase I movement of all univalents to one pole, thereby bypassing the reductional division but with 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.