Origin of Neopolyploids by Sexual Polyploidization in Turnera sidoides L. (Passifloraceae, Turneroideae)

CONTRERAS, FELIX IGNACIO; KOVALSKY, IVANA EVELIN; SOLÍS NEFFA, VIVIANA GRISELDA

Foz do Iguaçu

Congreso; 21st International Chromosome Conference (ICC); 2016

Turnera sidoides (x = 7) autopolyploid complex is a suitable model to analyze neopolyploid evolution in natural populations. Here, we analyze natural diploid populations of this species aiming to (1) estimate the frequency of neopolyploids and analyze their mechanism of origin, (2) analyze the spatial distribution of cytotypes and 2n gametes producers at a microscale, (3) estimate the viability and ploidy level of offspring of intercytotype matings, (4) analyze triploids cytogenetically, and (5) estimate the expected rates of neopolyploid formation. The finding of 3.5% triploid embryos contrasts with the rarity of triploid plants detected in natural diploid populations. The 2n gametes involved in neopolyploid formation were mostly of paternal origin. A spatial segregation of cytotypes was detected, although mixed 2x?3x patches were found. In such patches, 2n eggs and/or 2n pollen producers were detected.Triploids produce some n and 2n viable gametes and diploid, triploid,and tetraploid progeny in experimental crosses. The expected neopolyploid formation rates involving 2n pollen were 0.034 (triploids) and 0.00033 (tetraploids), and 0.025 (triploids) and 0.00025 (tetraploids) involving 2n eggs. The rate of neotetraploid formation by bilateral polyploidization was 0.00027. These results suggest that unilateral polyploidization would constitute an alternative mechanism of neopolyploids origin in T. sidoides . The rates of neopolyploid formation estimated are consistent with the expected rates in cross-pollinated autopolyploid species. The continuous formation of neopolyploids resulted from successive backcrosses between 2n gametes producers, and their progeny would favor the establishment and persistence of neopolyploids in diploid populations of T. sidoides . New generations of polyploids (triploids and tetraploids) would also originate by crossings between triploids or by backcrosses with diploid progenitors that produce 2n gametes. These facts together with the capacity of T. sidoides to multiply by rhizomes would enhance the likelihood that a low frequency of neopolyploids can be originated and maintained in natural diploidpopulations.