|
Genetic components: ms on a wheat chromosome An ideal ms mutant would have the following six characteristics: 1. A single recessive gene. 2. No selection against gametes bearing ms when in competition with gametes bearing the normal allele. 3. Stability in various varietal backgrounds. 4. Stability in various environments. 5. No pleiotropic effects of the ms mutant. 6. A suitable alien homoeologue. A number of male-sterile mutants of hexaploid wheat that have been reported in the literature are considered in the light of the above characteristics. PUGSLEY and ORAM (1959) reported male-sterile mutants in an F1 of Kenya Farmer X4 bearded Javelin 48. The inheritance was reported as being complex. BRIGGLE (1970) backcrossed this sterility into the variety Chancellor and by appropriate selection obtained a stock that involves a single recessive gene which is transmitted with reasonable rates from heterozygotes. Stability of this sterility is under investigation, and its chromosomal location is unknown. ATHWAL, PHUL and MINOCHA (1967) reported isolation of a male-sterile type in a complex hybrid. They also reported that the sterility is governed by mutiple factors and is perhaps unstable under various environments. KRUPNOV (1968) isolated a male-sterile mutant of the variety Saratovskaya-29 which may be controlled by a single gene. It was reported that male-sterile plants are less viable than fertile plants. FOSSATI and INGOLD (1970) isolated a male-sterile form of the variety Probus after applying 24 kR of X-rays to seed. The sterility was reportedly due to a single recessive gene that is normally inherited. Its chromosome location is unknown. It appears that this mutant may be suitable for the proposed system. Attempts are currently being made to isolated further ms mutants following gamma-irradiation of pollen of the variety Pitic 62. The technique involves pollination of monosomics 4A, 4B, 5A, 5B, or 5D with irradiated pollen. Each of these five chromosomes carries a gene or genes for male fertility, and it is known that only one arm of each of these chromosomes is involved (SEARS, personal communication). Thus a deletion including the Ms gene(s) would result in a male-sterile mutant. Monosomic F1's can be scored directly for such deletions. To date only chromosome 5B has been examined in this way. Although a number of male-sterile F1 hemizygotes were isolated and pollinated by euploid wheat, no sterile plants have been recovered in progenies derived from 42-chromosome offspring. The genetic basis of this is under investigation. One possible explanation centers on the fact that the male-sterile F1 plants are hemizygous 5B whereas all plants in later generations are homozygous 5B. One possible male-sterile mutant has been isolated and maintained following gamma-irradiation of monosomic 5A seed (GORMAN and DRISCOLL, unpublished). |
| <-- Back | | | --> Next |