| Source of meiotic abnormalities in barley-wheat hybrids
George FEDAK Ottawa Research Station, Research Branch, Agriculture Canada, ottawa, Ontario K1A OC6, Canada Hybrids between Betzes barley and Chinese Spring wheat were first reported by ISLAM et al., (1975) and subsequently other authors (FEDAK 1977a; CAUDERON et al., 1978). The hybrid plants in all cases had the expected somatic chromosome number of 28 and an irregular meiosis. Occassional PMC's with more than 28 chromosomes and some with up to 23 ring bivalents were reported by ISLAM et al. (1975). Similarly PMC's with chromosome numbers from 28 to 63 were reported in Betzes x Chinese Spring hybrids (FEDAK 1977b) and from 28 to 56 in the reciprocal cross (FEDAK 1980). Backcrossing of Chinese Spring onto the latter gave progeny with somatic chromosome numbers of 44 to 60, although 49 or less would have been expected. These progeny with excessive chromosome numbers undoubtedly arose from the union of 21 chromosome Chinese Spring gametes with hyperploid gametes from the hybrid that likely arose from hyperploid products of meiosis. Premeiotic mitosis in the hybrids was examined as a possible origin of hyperploid PMC's. Spikes collected at 72 hours prior to the PMC stage contained cells at prophase and metaphase of mitosis. Anthers for mitotic studies were squashed in acetocarmine or pretreated with Snow's solution prior to squashing in acetocarmine as in PMC studies. The majority of cells at premeiotic mitosis had 28 chromosomes, showed a 28-28 disjunction at anaphase, the products of which would presumeably produce normal gametes. A small proportion of cells, however, showed unequal disjunction at anaphase as shown in Fig. 1 which would lead to deficiency duplication PMC's; the latter eventually forming hyperploid gametes. Deficient cells likely were inviable since PMC's with less than 28 chromosomes were not encountered in the present study. Several other cytological abnormalities were detected in studies of meiosis of barleywheat hybrids and their progenies. Isochromosomes were observed in PMC's of Betzes x Chinese Spring hybrids (FEDAK, 1977b) and telocentric chromosomes in backcross progenies of the same hybrids. Telocentrics would result from misdivisions of the centromere and isochromosomes would result from them. Multipolar anaphase as shown in Fig. 2 was observed at premeiotic mitosis and could have caused misdivision of centromeres leading to the formation of the chromosome fragments observed. |
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