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 sp p) landraces is continuous and striking. For an inexperienced observer it is even difficult to distinguish their ploidy level (tetra- vs hex aploid) 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 abl e to detect any major deviation from the karyotype reported in the lit erature. Seventy-four wheat landrace morphotypes collected from four l ocalities in the central highlands of Ethiopia were used. Sixty-nine m orphotypes were tetraploid while live were hexaploid (2n = 6x = 42), s uggesting the need for chromosome number confirmation whenever there i s a doubt. The Q-factor complex, either introgressed from the hexaploi ds to the tetraploids or directly introduced as in T. carthlicum (2n = 4x = 28), seemed to have been responsible for the morphological overl apping. No aneuploidy was encountered. Genotypic differences in the re solution of nucleolus organizing regions were observed. The tetraploid s, as a whole, had pairs of two satellited. eight median and four subm edian chromosomes. The notable deviation detected was the fixed altere d centromeric position of chromosome 6B in three morphotypes collected from three different localities. Unlike the 'normal' situation the sa tellite was attached to the longer arm. No connection was established between this rearrangement and the conspicuous variation for spike mor phology or other useful agronomic traits including fertility. This may indicate a minor role for chromosomal rearrangement in either the mor phological diversity or fitness characters of the wheat landraces. Des pite the presence of cytotypes, however, chromosome-arm ratio remained highly stable after centuries of wheat cultivation in Ethiopia.