UNREDUCED POLLEN IN HEXAPLOID SWEET-POTATO (IPOMOEA-BATATAS)

Recent observations of unreduced 2n pollen in diploid and tetraploid relatives of hexaploid sweetpotato [Ipomoea batatas (L.) Lam] can be considered indirect evidence that unreduced pollen has played a major role in polyploidization of hexaploid l. batatas (Jones 1990; Orjeda et al. 1990). To further study the role of unreduced pollen in sweetpotato evolution, pollen from five cultivars and 100 genetically diverse sweet potato seedlings was examined for the presence of unreduced pollen. Two individuals of tetraploid accession 81.2, T-1 and T-2 that had previously been identified as having high levels of unreduced pollen, were used as controls. High levels of unreduced pollen were confirmed in these tetraploids, and low levels were observed in 16% of the hexaploids. The presence of monad, dyad, and triad sporads confirmed that the large-size pollen resulted from nonreduction during meiosis; these structures were not observed in plants containing only normalsize pollen. These findings are direct evidence that unreduced 2n pollen was involved in the evolution of l. batatas to the hexaploid level. The widespread presence of this genetic condition in l. batatas suggests that use of this trait to introgress genes from wild 4x Ipomoea species should not necessarily affect genetic stability or fertility. © 1994 The American Genetic Association.