The mentor effect increases the rate of selfing in couch grasses

Some self-incompatible species are thought to be capable of selfing via facilitation by foreign pollen (induced selfing or the mentor effect), which might be a phenomenon of underestimated importance. In addition, higher percentages of selfing are linked to polyploidy. Grasses are a very important plant group, but the degree to which they are capable of selfing (including via the mentor effect) has scarcely been investigated. We selected Elymus hispidus, E. repens and their hybrid (Poaceae tribus Triticeae) as model taxa in order to test their ability to reproduce by selfing, to assess the significance of induced selfing, and to examine the assumed link between selfing and ploidy level (particular cytotype). Because absolute genome size of the model species of Elymus differs significantly, we used flow cytometry as a marker for identifying selfing as opposed to outcrossing based on comparing parental plants with their progeny. The ability for selfing and induced selfing was determined in two complementary crossing experiments supplemented by an open-pollination control treatment. The results confirm that both species and their hybrid are capable of selfing and that the percentage of selfing increased significantly in the presence of foreign pollen. This is especially marked in Elymus hispidus (the realized seed set in autonomous selfing was 6.2% compared to 22.7% in induced selfing). Octoploids selfed more often than hexaploids and heptaploids, and heptaploids produced significantly fewer seeds after selfing than hexaploids and octoploids. The pronounced selfing ability in E. hispidus (observed in both experiments) may be linked to introgression. Despite probably being a very important reproductive feature, the significance of induced selfing (i.e. the mentor effect) is definitely underestimated.