Self‐sterility in <i>Epilobium obcordatum</i> (Onagraceae)

Abstract

Greenhouse pollinations among 23 field‐collected plants and their progeny revealed a high and variable degree of self‐sterility in Epilobium obcordatum. Field‐collected plants averaged 5% seed‐set when selfed and 43% seed‐set in crosses; greenhouse progeny 11% and 49%, respectively. In two of three pollen chase tests, previously or simultaneously applied self‐pollen reduced seed‐set to that resulting from pure self‐pollination. Based on the relative survivorship of self‐ and outcross embryos, the mean number of lethal equivalents was determined to be 11.0 (range 2.9 to 17.6) in the field‐collected plants, and 7.1 (range 0.62 to 21.8) in the greenhouse progeny. Pollinations among 91 individuals showed a significant negative correlation between seed‐set and inbreeding coefficients of the resulting zygotes. Intrapopulation crosses yielded significantly fewer seeds than interpopulation crosses. Early embryonic mutational load, in combination with some level of biparental inbreeding, appears to be responsible for the level of self‐sterility in natural populations of this species. A pollen dosage test for an interpopulation cross resulted in a maximum seed set of 47% at 16 tetrads. Additional unmeasured characteristics govern the probability of ovules becoming mature seeds.