Cytology of the autotriploid Allium rubellum.

Abstract

Of A. rubellum, already known as a diploid (2n=16), a triploid form has been collected from Pathankot. All the 24 chromosomes in the latter possess median to submedian kinetochores. Of these, 6 are nucleolar chromosomes, which do not represent 3 truly morphologically homologous pairs. Meiosis is characterised by the presence of quadrivalents, trivalents, bivalents and univalents. Out of these, trivalents are the most common and often as many as 8 were seen in a cell. Anaphase-I distribution is irregular and shows bridge-fragment configurations, lagging chromosomes and micronuclei. The subsequent course of meiosis is also not normal and results in sterility. In view of the high frequency of trivalents, the triploid form appears to be an autotriploid and the karyotypic heterozygosity points to an intervarietal origin. It maintains itself because of the efficient vegetative reproduction.