GrainGenes
A Database for Triticeae and Avena
Fukuyama and Hosoya, pp. 47-50
II. 18. Time, pattern and genetic control of chromosome elimination in interspecific hybrids between 4X Hordeum bulbosum L. and 4X H. vulgare.
L. T. Fukuyama and H. Hosoya, The Ohara Institute for Agricultural Biology, Okayama University, Kurashiki, Okayama, Japan.
Kao and Kasha (1970) first reported that the interspecific cross between 4X H. bulbosum and 4X H. vulgare often gave the vulgare-like dihaploid F1 plants following the selective elimination of bulbosum chromosomes. Thereafter, Fukuyama and Takahashi (1976) demonstrated that the frequency of dihaploid plants appeared among the F1 hybrid plants was markedly different with the strains of H. bulbosum, but not those of H. vulgare: for instance, it was as high as 80% when a bulbosum strain #191 was used as the parent, whereas it was only 20% in a cross of a bulbosum strain #487 with the same vulgare strain. This experiment was undertaken to know the pattern and genetic control system of chromosome elimination in the interspecific hybrid plants.
Two strains of H. bulbosum, #191 and #487, were reciprocally crossed to a 4X H. vulgare strain D8/55. Forty caryopses from each cross were taken on 3, 5, 7, 9, 11 and 13 days after pollination, and stored in cold water (o°C) for 24 hours. They were then fixed with 1:3 acetic alcohol for 24 hours and stained with aceto carmine.
Fig. l-a shows the changes of chromosome number in the F1 embryos taken from the reciprocal crosses between #191 and D8/55 on 3, 5 and 13 days after pollination. Among the 3 day old embryos, the cells with 2n=26~28 were most frequent, varying from 28 to 14 in chromosome number. However, on 5 days after pollination, the cell with 14 chromosomes rapidly increased up to 43~51%, while the frequencies of cells containing more than 15 chromosomes became relatively few. The frequency of the cells containing dihaploid chromosome number gradually increased thereafter and attained up to 74 -80% on 13 days after pollination. It is apparent in the figure that the hybrids from the reciprocal crosses behaved almost similarly.
Fig. 1. Frequency distribution of chromosome number
in embryos of reciprocal F1 hybrids between D8/55 and two strains of H.
bulbosum, #l91(a) and
#487(b) on 3 different days after pollination.
The results of the hybrid between #487 and D8/55 were somewhat different. As shown in Fig. l-b, the frequency curve for 5 day old embryos became bimodal with its bottom at 17 chromosomes. In 13 day old embryos, the frequency of the cells with 2n=14 attained 20%, while the remaining cells involved 16 to 28 chromosomes.
Next, Fig. 2 was prepared in order to show how the changes after pollination occurred in frequency of hybrid embryos with less than 16 in chromosome number. In both reciprocal crosses, the dihaploid embryos rapidly increased 3 to 5 days after pollination, and reached a plateau in 9 days, although, as stated before, the dihaploid frequency in the cross of #487 and D8/55 was markedly fewer than that in #191 and D8/55. It must be mentioned here that an abrupt increase in dihaploid frequency was observed among the hybrid between #487 and D8/55 after 11 days. This was a rather unexpected event, but it may be supposed to be due to the heterogeneity of #487 clone for the character eventually used as the mother plant.
From these results, it may be safe to conclude that the chromosome elimination in the F1 hybrid plant between bulbosum and vulgare occurs concentrically around 3 to 5 days after pollination, and this is controlled by the nuclear gene(s) involved in bulbosum, but not by the cytoplasmic gene(s) in parental species.