Change in nuclear DNA content and pollen size with polyploidisation in the sweet potato (Ipomoea batatas, Convolvulaceae) complex
Résumé
Genome size evolution, and its relationships with pollen grain size, has been investigated in the sweet potato (Ipomoea batatas), an economically important crop, and closely related diploid and tetraploid species, assessing the nuclear DNA content of 22 accessions from five Ipomoea species, 10 sweet potato varieties and two outgroup taxa. Nuclear DNA amounts were determined by flow cytometry. Pollen grains have been studied at scanning and transmission electron microscopy. 2C DNA content of hexaploid I. batatas ranged over 3.12-3.29 pg, mean monoploid genome size being 0.539 pg (527 Mbp) much as for the related diploid accessions. In tetraploid species I. trifida and I. tabascana, 2C DNA content was respectively 2.07 and 2.03 pg. In the diploid species closely related to sweet potato e.g. I. ×leucantha, I. tiliacea, I. trifida, I. triloba, 2C DNA content was 1.01-1.12 pg. However, two diploid outgroup species, I. setosa and I. purpurea, were clearly different from the other diploid species with 2C of 1.47-1.49 pg; they also have larger chromosomes. The I. batatas genome presents 60.0% of AT bases. DNA content and ploidy level were positively correlated within this complex. In I. batatas and the more closely related species I. trifida, genome size and ploidy levels were correlated with pollen size. Our results allow us proposing alternative or complementary hypotheses to the one currently proposed for the formation of hexaploid Ipomoea batatas. This article is protected by copyright. All rights reserved.