“The role of triploids on the origin, establishment and coexistence of tetraploids with diploids in natural populations of Turnera sidoides autopolyploid complex”

KOVALSKY I.E., G ELÍAS, S MORENO, A PANSERI & SOLÍS NEFFA VG

San Carlos de Bariloche, Argentina

Congreso; VI SOUTHERN CONNECTION CONGRESS; 2010

Universidad Nacional del Comahue, CONICET, INTA

The role of triploids on the origin, establishment and coexistence of tetraploids with diploids in natural populations of Turnera sidoides autopolyploid complex Kovalsky IE1*, G Elías1, S Moreno1, A Panseri1 & Solís Neffa VG1,2. 1Instituto de Botánica del Nordeste (UNNE- CONICET). CC 209. 3400, Corrientes (Argentina). 2Facultad de Ciencias Agrarias (UNNE). (evelinkov@hotmail.com). Theory suggests that the evolution of autotetraploids within diploid populations is opposed by a minority cytotype mating disadvantage, since rare tetraploids incur in a larger portion of hybrid matings that yield inviable triploid progeny (triploid block). Turnera sidoides (x=7) is used as a model system to evaluate the role of triploids on autotetraploid evolution in natural populations. This complex of perennial rhizomatous herbs is widely distributed in southern South-America and shows ploidy levels from diploid to autooctoploid. The finding of triploids in natural populations and in experimental crosses evidences a lower triploid block in this species. Thus, our objectives were to: 1) estimate the frequency of neopolyploids in diploid populations and analyze their mechanism of origin; 2) evaluate the frequency and distribution of cytotypes in two diploid-tetraploid contact zones; 3) estimate fecundity and offspring ploidy in matings among diploid, triploid and tetraploid in all possible combinations. The finding of 3.5% triploid embryos contrasts with the rarity of triploid plants observed in natural diploid population. The 2n gametes involved in triploid formation were mostly of paternal origin. Within the contact zones, spatial segregation of cytotypes was seen although, mixed 2x-3x populations were also found. Triploids produced x or 2x euploid gametes in equal proportion, however no tetraploid offspring resulted. The results obtained suggest that in T. sidoides although triploids can potentially contribute to the formation of tetraploids by a triploid bridge as well as to the maintenance of the current cytotype distribution within the contact zone, the contribution to tetraploid establishment is minor.