Evidence of the production of 2n eggs in diploid plants of the autopolyploid complex Turnera sidoides L. (Passifloraceae)

Abstract

Turnera sidoides is a complex of dystilous perennial rhizomatous herbs with five subspecies in which diploid (2n = 2x = 14) to octoploid (2n = 8x = 56) cytotypes were found. Previous studies have suggested an autopolyploid origin of the complex, and provided evidence for the production of 2n pollen in experimental conditions as well as in natural populations. However, only the production of 2n pollen has been demonstrated so far, while the production of 2n eggs on experimental crosses or in natural populations of T. sidoides remains unknown. In this paper we investigate the production of 2n eggs in diploid individuals to understand how they may have contributed to the origin and establishment of polyploids in diploid populations of T. sidoides. Our progeny test and flow cytometric analysis of seeds collected in natural populations of this species complex, show that the triploid embryos originated from 2n eggs, suggesting that 2n eggs can contribute to the origin of neopolyploids by sexual unilateral polyploidization as well as by sexual bilateral polyploidization. The occurrence of plants that continuously form many 2n eggs and pollen would play a key role in the establishment of neopolyploids in natural diploid populations.