CYTOGENETIC STUDIES IN ETHIOPIAN LANDRACES OF TETRAPLOID WHEAT (TRITICUM-TURGIDUM L) .1. SPIKE MORPHOLOGY VS PLOIDY LEVEL AND KARYOMORPHOLOGY

The variation for spike morphology in the Ethiopian wheat (Triticum spp) landraces is continuous and striking. For an inexperienced observer it is even difficult to distinguish their ploidy level (tetra- vs hexaploid) based only on morphological characteristics. The objectives of this study were to determine the concordance of spike morphology with ploidy level and to characterize the chromosomes of the tetraploids (2n = 4x = 28) according to their centromeric positions so as to be able to detect any major deviation from the karyotype reported in the literature. Seventy-four wheat landrace morphotypes collected from four localities in the central highlands of Ethiopia were used. Sixty-nine morphotypes were tetraploid while live were hexaploid (2n = 6x = 42), suggesting the need for chromosome number confirmation whenever there is a doubt. The Q-factor complex, either introgressed from the hexaploids to the tetraploids or directly introduced as in T. carthlicum (2n = 4x = 28), seemed to have been responsible for the morphological overlapping. No aneuploidy was encountered. Genotypic differences in the resolution of nucleolus organizing regions were observed. The tetraploids, as a whole, had pairs of two satellited. eight median and four submedian chromosomes. The notable deviation detected was the fixed altered centromeric position of chromosome 6B in three morphotypes collected from three different localities. Unlike the 'normal' situation the satellite was attached to the longer arm. No connection was established between this rearrangement and the conspicuous variation for spike morphology or other useful agronomic traits including fertility. This may indicate a minor role for chromosomal rearrangement in either the morphological diversity or fitness characters of the wheat landraces. Despite the presence of cytotypes, however, chromosome-arm ratio remained highly stable after centuries of wheat cultivation in Ethiopia.