Previous work in this laboratory identified high levels of unreduced (2n) pollen in the tetraploid (4×) Ipomoea spp. Acc. 81.2. This work provided indirect evidence that 2n pollen was involved in the evolution of the 6x ploidy level of the cultivated sweetpotato (I. batatas). To further study the role of 2n pollen in sweetpotato evolution, we examined plants of Acc. 81.2. plants of five sweetpotato cultivars, and 100 randomly selected heterozygous sweetpotato seedlings. The 4× Acc. 81.2 was determined to be I. batatas. High levels of large 2n pollen were confirmed in Acc. 81.2, and low levels of 2n pollen were observed in `Sulfur' and in 16% of the sweetpotato seedlings. Presence of monad, dyad, and triad sporads confirmed that the large 2n pollen grains were the result of nonreduction in the sporad stage. These new findings are direct evidence that 2n pollen was involved in the evolution of the 6× ploidy level of sweetpotato. This is the first report of a 4× accession classified as I. batatas; it is also the first report of 2n pollen in 6× I. batatas The widespread presence of 2n pollen in sweetpotato suggests that the trait can be used to advantage in breeding programs to introgress genes from wild 4× Ipomoea spp. into cultivated 6× sweetpotato without adverse effects on genetic stability or fertility.
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