DELAYED POLLINATION, STIGMA LENGTH, SEX EXPRESSION, AND PROGENY SEX-RATIO IN SPINACH, SPINACEA-OLERACEA (CHENOPODIACEAE)

Delayed outcrossed pollination of female spinach plants (Spinacea oler acea L.) resulted in increased stigma length and a male-biased progeny sex ratio. One group of females was outcrossed 10-14 d after anthesis , a second group was never outcrossed, and a third group, the control, consisted of females that were outcrossed as soon as stigmas appeared . Stigma length was significantly greater for plants in the delayed an d never outcrossed groups compared to the control. Furthermore, stigma s of virgin flowers grew until they were either pollinated or the plan ts produced anthers. Plants that were never outcrossed produced their own anthers and self pollinated. The resulting progeny were all female . The sons of the delayed outcrossed group produced more stamens, on a verage, than sons of the control group. The observed male-biased sex r atio among the progeny of delayed outcrossed plants could be due to ga metic selection. To test for this, plants were held virgin until their stigmas reached a length of at least 3 mm. These stigmas were then po llinated either distally or proximally. No significant difference was found between the progeny sex ratios of these two treatments. However, both sex ratios were more male biased than progeny of plants pollinat ed the day of anthesis (control group of the first experiment). We con clude that maternal factors, rather than gametophytic selection, may b e responsible for the male-biased sex ratio observed in the first expe riment.