Self-pollination rates in US breeding populations of hairy vetch and smooth vetch

Hairy vetch (Vicia villosa Roth) and smooth vetch (Vicia varia Host) are legume cover crops with strong winter survival and biomass productivity. Both species tend toward outcrossing but are also self-compatible, suggesting that the species are mixed mating. This study quantified self-pollination rates and inbreeding depression in V. villosa and V. varia within an active US breeding program using single sequence repeat markers. Self-pollination rates were determined using parents and progeny samples in 172 half-sib families (n = 2370 progeny). Progeny with more than one allele varying from the maternal parent were considered the result of cross-pollination. Parent–progeny samples were collected from early-cycle mothers with unselected progeny seed, early-cycle mothers with low-selection-intensity progeny plants, and advanced-cycle mothers with high-selection-intensity progeny plants. Mean self-pollination rate across all samples was 13.0%, with strong variation among families (0%–81%). Unselected progeny seed had low self-pollination rates (4.8%) relative to early-cycle progeny (27.6%) and advanced-cycle progeny (21.6%). Species identity did not impact self-pollination rate, but both parent growing environment and breeding germplasm source had significant but minor (p < 0.05) effects. Self-pollinated offspring had inbreeding depression for biomass (−48%), seed yield (−45%), plant maturity, seed dormancy, and pod dehiscence. These results confirm that these two cover crop vetch species are mixed-mating systems. The strong skew in self-pollination rates among families is an unexpected observation that parallels other reports from mixed-mating species. Skewed self-pollination rates pose a practical challenge for breeding programs and may have implications for the prevalence of mixed mating in natural systems.