Chromosome studies in Allium sativum

Abstract

The chromosomes were studied in 4 strains of garlic, Allium sativum, belonging to 2 different morphologic types, 3 strains to the so-called H type and 1 strain to the U type. Since Allium sativum never sets any seed, each strain can be regarded as a clone. One aim of the study was to define whether their genetic isolation had resulted in the accumulation of chromosomal differences between the clones. It was demonstrated by measurements of all chromosomes of 55 root mitoses that the karyotypes of the clones, although generally maintaining their differentiation in 2 homologous sets, exhibited a significantly higher variation between clones than between cells within clones, the parameters studied being total chromosome length, arm ratio and 2 satellite indices. The differences were especially pronounced in the 2 satellite-carrying chromosome pairs. The results of the measurements were born out by observations on meiosis: even though normal bivalent formation characterized the 2 clones of the H type studied (the U type could not be studied, because it very rarely forms flowers), meiotic disturbances were frequent, indicating small structural differences between the homologues. In one of the clones a large structural change, a ring of 4 chromosomes, was observed regularly at first meiosis. The implications of our observations for karyotypic evolution in Allium are discussed.