DETERMINATION AND ANALYSIS OF SOMATIC CHROMOSOME NUMBERS IN SWEETPOTATO CULTIVARS, RELATED Ipomoea SPECIES, AND INTERSPECIFIC HYBRIDS

Abstract

The somatic chromosome numbers (2n) in seven sweetpotato cultivars, four diploid (2x) Ipomoea species, tetraploid (4x) and hexaploid (6x)1. trifida strains, and twenty selected hybrids between sweetpotato and 6xl. trifida were determined using a Feulgen-acetocarmine squash technique designed forIpomoea chromosomes. The data revealed that euploid counts of 2n-30, 60 and 90 were the modes for the 2x, 4x, and 6x Ipomoea, respectively. These counts coexisted with aneuploid cells having either less (hypoploid) or more (hyperploid) chromosomes than the euploid or modal counts. The hypoploid cells were majority among the aneuploid variants. The percentage frequency ratio of euploid to aneuploid cells were 60%:40% among diploids, 45%:55% among tetraploids, and 30%:70% and 34%:66% among the 6x I trifida and sweetpotatoes, respectively. The wide hybrids exhibited extreme aneuploidy with 16%:84% euploid to aneuploid cell ratio. Two hybrids did not show cells with 2n=90. In general, the hybrids resembled the sweetpotato parents in having chromosome numbers closer to 6x or 90 whereas the 6xl. trifida and the 4x strains exhibited somatic counts encompassing the 2x, 4x and 6x counts. The results suggest that the prevailing cytogenetic system among thelpomoea is that of somatic euploidy-polyploidy combined with aneuploidy. Further, the amount of aneuploid cells appeared higher with taxa of higher ploidy and highest among the hybrids. The findings are discussed in relation to sweetpotato breeding, germplasm conservation and evolution of new phenotypes through vegetative propagation.