STUDIES ON THE RELATIONSHIP OFAVENA SATIVA(6x) ANDAVENA HIRTULA(2x)

Introdnction Information on the genomic relationships between Avenn species of different ploidy levels is based on chromosome pairing in F, hybrids. Rajhathy and Morrison (1960) studied chromosome pairing in hybrids between species of different ploidy and concluded that the genomic designation of the diploid species should be AA, the tetraploids AABB, and hexaploids AACCDD. Marshall and Mycrs (1961) reported that most of thc bivalents formed in the F, hybrids bctween A. strigosn and A. sntivn were rods with a single chiasma. Thomas and Jones (1964) observed a similar pattern in cl~roinosome pairing in the F, hybrid between A. abysshzica and A. sativn. I t was inferred in both papers that this low number of chiasmata per bivalent could be an indication of reduced affinity bct~veen the A genomes of the diploid species and those of the tetraploid and hcxaploid species. Chromosome repatterning has occurred in chromosome complements of the diploid species of Avenn as revealed by the ltaryotypes of the A. strigosn group, A. lo7zgiglz~nzis and A. pilosn (Rajhathy, 1961: Rajhathy and Dyck, 1963). In this paper we report further data on the relationship between diploid and hexaploid species as revealcd by the pattcril of chromosome pairing in the amphiploid dcrived from the A. hirtz~ln X A. sntivrr F, hybrid, and in the first backcross hybrid to A. sntivn. Material and Method T w o F, hybrids between A. hirtala Lag; (CC3678) 272 = 14, and A. sntivn cult. Manod 272 = 42, wcre successfully treated with 0.2% colchicine solution using the capping technique of Bell (1950). The derived amphiploids (A,) were back-crossed to A. sntivn. Panicles of the amphiploid plants and the back-cross hybrids (BC,) were fixed in carnoy fixative (6:3: 1) and stored in a refrigcrator for three wcelts bcfore esamination. The anthers were stained in alcoholic acid accto-carmine stain, as described by Snow (1963), and chromosomc pairing was studied at A41 in Squash preparations. Seed setting was recorded in A, and BC, plants grown under field conditions. The morphology of the A, and BC, plants was studicd under similar conditions. Results Morphology of the n7nplgiploid and BC, k y brids In the juvenile stage, both the amphiploid and BC, plants manifested a prostrate, high-tillcring growth habit, similar to, although not as pronounced as, that found in A. hi~tz~ln. Plant height at maturity approached that recorded for A. sntivn, and the panicles, ~vllcn fully emcrged, closely resembled those of A. sntivrr. The dark grain colour of A. I~i~tz~ln was incompletely expressed as a grcyish blotch on the inner pale of the amplliploid and BCI seeds. The intensity and size of the blotch varied from panicle to panicle, but we had no difficulty in detecting it evcn when it was poorly expressed. The lower spikelet had a strong geniculate awn, typical of A. hirtzlln.