Haploidy in the genus Aegilops

V. CHAPMAN and T.E. MILLER

Plant Breeding Institute, Kambridge, England

Because of their low spontaneous frequency, haploids have been reported only in the diploid species Aegilops caudata (CHAPMAN and RILEY 1964) and Ae. longissima (RILEY and CHAPMAN 1957) and in the tetraploid Ae. ovata (MATSUMURA 1940). Recently, however, high frequencies of haploids of barley (KASHA and KAO 1970) and of wheat (BARCLAY 1975; MILLER and CHAPMAN 1976) have been obtained from crosses with Hordeum bulbosum. This report describes the application of this method to the production of haploids in tetraploid Ae. triuncialis and hexaploid Ae. crassa.

Emasculated ears of Ae. triuncialis (2n=28) and Ae. crassa (2n=42) were pollinated with pollen from plants of tetraploid H. bulbosum. Grains resulting from these pollinations were removed after 14 days. Embyros which had developed in some grains were cultured on standard orchid agar medium. Three haploid plants of Ae. crassa and one of Ae. triuncialis were established by this procedure.

KIHARA (1954) by genome analysis concluded that the two putative parents of Ae. triuncicalis were Ae. caudata (C) and Ae. umbellulata (C^u) and assigned to it the genome formula CC^u. In a hybrid between these two diploid species the mean pairing at meiosis was much higher than that now found in the haploid Ae. triuncialis. By the use of a similar analysis KIHARA et al. (1959) also found that in hexaploid Ae. crassa there were two closely related genomes which had originated from diploid Ae. squarrosa (D). The meiotic analysis of haploid Ae. crassa does not provide evidence to support the proposed genome formula DD²M^CR. In the haploid there was a much lower frequency of bivalents than might have been expected to result from the pairing of two closely related genomes.

In both haplid Ae. triuncialis and Ae. crassa the meiotic pairing levels were lower than would have been predicted from the evidence of genome analysis. Either the genomes within the two species are less closely related than suggested by genome analysis or a form of genetic control of chromosome pairing restricts the pairing between homoeologous chromosomes of the genomes.

The wheat and barley haploids were formed by the elimination of H. bulbosum chromosomes in the early mitotic divisions of the hybrid embryos. If, as seems likely, the haploids in this experiment resulted from a similar procedure of chromosome elimination it may be possible to obtain haploids from all the polyploid species in the genus Aegilops. Such haploids would provide evidence which would assist the understanding of genome relationships and the control of meiotic chromosome pairing in the Triticinae.

Table 1. Mean chromosome pairing at first metaphase of meiosis (30 cells per plant)

Literature Cited

BARCLAY, I.R. 1975. High frequencies of haploid production in wheat (Triticum aestivum) by chromosome elimination. Nature 255: 410-41l.

CHAPMAN, V. and R. RILEY 1964. Haploid Aegilops caudata. Wheat Inf. Serv. 17: 16.

KASHA, K.J. and K.N. KAO 1970. High frequency haploid production in barley (H. vulgare). Nature 225: 874-875.

KIHARA, H. 1954. Considerations on the evolution and distribution of Aegilops species based on the analyser-method. Cytologia 19, 336-357.

KIHARA, H., K. YAMASHITA and M. TANAKA 1959. Genomes of 6x species of Aegilops. Wheat Inf. Serv. 8: 3-5.

MATSUMURA, S. 1940. Induzierte Haploidie und Auto-tetraploidie bei Aegilops ovata. Bot. Mag. Tokyo 54: 404-413.

MILLER, T.E. and V. CHAPMAN 1976. Aneuhaploids in bread wheat. Genet. Res. 28: 37-45.

RILEY, R. and V. CHAPMAN 1957. Haploids and Polyhaploids in Aegilops and Triticum. Heredity 11: 195-207.

(Received Nov. 25, 1976)