Genome Analysis of Amaranthus dubius Mart. ex Thell. through the Study of Amaranthus spinosus×A. dubius Hybrids

Abstract

Hybrids between Amaranthus spinosus L, (n-=17), a diploid and A. dubius Mart. ex Tell. (n=32), a tetraploid compared to A. spinosus frequently arise in nature where both the species grow together. Cytological analysis of such triploid hybrids, the hexaploids raised through colchicine treatment and certain deviant hexaploids, mainly found among the progeny of the second and third generation hexaploids revealed interesting genome relationships between A. dubius and A. spinosus. In the pollen mother cells of the triploid hybrid (2n=49) various types of chromosomal associations could be seen ranging from 22^II+5^I to 4^IV+9^II+15^I with a high frequency of 17^II+15^I. In view of this the possibilities of only autosyndesis or only allosyndesis were eliminated and this was strongly suggestive of the presence of three sets of genomes in the triploid hybrid with both auto- and allosyndesis. The observed frequency of bivalent distribution was strongly deviating from the expected frequency of binomial distribution and the pattern of deviation with a modal value of 17 bivalents may suggest that a set of chromosomes genetically comparable to those of A. spinosus is present within A. dubius genome.