Sex ratio of Rumex acetosa seeds obtained from pollination within and between populations

Rumex acetosa L. (common sorrel) is a dioecious, wind pollinated plant with an XX/XY1Y2 sex chromosome system. Sex-ratio in the populations of dioecious plants is rarely even; generally it is skewed towards one gender. Rumex populations showed female sex-ratio bias at all of the stages of development, but the difference in sex proportion was smaller in earlier stages (Stehlik et al. 2008). Moreover, sex-ratio bias varied in different populations of the same species (Zarzycki & Rychlewski 1972). The possible causes of unequal proportion of males and females are: certation, sex-dependent germinability of seeds, and/or difference in mortality of gametophytes, embryos, and plants (BA‚ocka-Wandas et al. 2007). The plants originating from two distant populations in S Poland (Dobranowice and Wieliczka) were isolated and pollinated in a controlled condition to minimize the influence of certation. The pollinations were following: DW – ♀ from Dobranowice and ♂ from Wieliczka, WD – ♀ from Wieliczka and ♂ from Dobranowice, and DD – ♀ from Dobranowice and ♂ from Dobranowice. Seeds obtained from each experiment were collected and examined for sex by PCR. Two pairs of PCR primers that amplify sequences located in Y chromosomes were used: RAY-f and RAY-r (Korpelainen 2002), and UGR08-r and UGR08-f (Mariotti et al. 2009). To confirm the good quality of isolated DNA an amplification of autosomal sequence using R730-a and R730-b primers were carried out (Navajas-Perez et al. 2005). The same set of primers was successful in our previous studies on sorrel (Kwolek & Joachimiak 2010). Sex ratios of WD and DW seeds were similar, but clearly differed from the observed in DD seeds (Tab. 1). Progeny produced by parents from different populations showed much larger proportion of females than progeny of parents originated from the same population. The finding requires further investigations to verify the results and to explain the mechanisms underlying the observed phenomenon.