GrainGenes

II.36 Interspecific hybridization, chromosome elimination and haploidy in Hordeum.

N.C. Subrahmanyam, Genetics Department, Research School of Biological Sciences, The Australian National University, Canberra, A.C,T. 2601. Australia. "R"

Chromosome elimination has been observed in interspecific Hordeum hybrids for over 20 years and 7 such hybrid combinations were reported to result in haploids (Kasha, 1974). To elucidate the distribution of chromosome elimination in other interspecific Hordeum hybrids, crosses between different species are being made following the techniques of Subrahmanyam and Kasha (1973a,b).

The progenies obtained from various parental combinations are presented in Table 1. The chromosome numbers were determined after the establishment of the seedlings in pots. For the crosses procerum by bulbosum (2x or 4x) or vulgare (2x), haploids were morphologically similar to procerum. The haploids from the cross parodii by bulbosum (2x) were similar to parodii. Morphologies of the hybrids from various crosses were somewhat variable. Hybrids from the crosses involving bulbosum as one of the parents showed more bulbosum characteristics and usually were late maturing.

Table 1. Progeny obtained from Hordeum interspecific crosses

Embryos from various crosses were cytologically examined to check chromosome variability. The cytological observations on the embryos are consistent with the results for the crosses listed in Table 1, i.e. chromosome elimination occurs in the embryos from the crosses resulting in haploids.

Chromosome variations in the embryos for additional crosses are presented in Table 2. The variations from the expected hybrid complement (2n=14) to a haploid number (7) is indicative of chromosome elimination. It is not certain at this stage which chromosomes are eliminated in the crosses Stebbinsii by bulbosum and flexuosum by vulgare. Because the chilense (2x) by bulbosum (2x) cross (Table 1) resulted in hybrids (i.e., bulbosum chromosomes are retained), it is likely that chilense chromosomes are selectively eliminated in the chilense-vulgare cross (Table 2). Abnormalities such as micronuclei, dense chromatin bodies and degraded chromatin are also observed in embryos where chromosome variability is evident.

Table 2. Chromosome variations in embryos from Hordeum interspecific crosses.

The presence of haploids in the crosses procerum or parodii with diploid bulbosum and hybrids with tetraploid bulbosum, indicates that the parental genomic ratio is an important factor for chromosome stability or elimination. These principles have already been demonstrated for crosses between vulgare and bulbosum (Subrahmanyam and Kasha, 1973b; Ho and Kasha, 1975). Formation of haploids and hybrids in the cross procerum by bulbosum (4x), hybrids from the cross parodii by bulbosum (4x), haploids of procerum from procerum-vulgare cross and hybrids from parodii-vulgare cross, suggest that procerum has a stronger genetic mechanism for the elimination of bulbosum or vulgare chromosomes. Clearly a hierarchy of chromosome elimination can be established in Hordeum.

Acknowledgements:

I wish to sincerely thank Dr. D.R. Dewey, Utah State University, Logan, U.S.A. and R. R. Oram, Division of Plant Industry, C.S.I.R.O., Canberra for the supply of seeds of different species used in this study. Technical assistance of Miss K. Ferguson and encouragement of Dr C.H. Doy are highly appreciated

References:

Ho, K.M. and K.J. Kasha. 1975. Genetic control of chromosome elimination during haploid formation in barley. Genetics, 81: 263-275.

Kasha, K.J. 1974. Haploids from Somatic Cells, p. 67-87 in "Haploids in Higher Plants - Advances and Potential" ed. K.J. Kasha.

Kasha, K.J. and K.N. Kao. 1970. High frequency haploid production in barley (Hordeum vulgare L.) Nature, 225: 874-876.

Subrahmanyam, N.C. and K.J Kasha. 1973a. Feeding of detached tillers improves haploid production in barley. BGN 3: 62-65.

Subrahmanyam, N.C. and K.J. Kasha. 1973b. Selective chromosomal elimination during haploid formation in barley following interspecific hybridization. Chromosoma (Berl.) 42: 111-125.

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