Self-pollination rates in U.S. breeding populations of hairy vetch and smooth vetch

Authors: Tilhou, Neal; Riday, Heathcliffe; VANG, MAIYER - University Of Wisconsin; Mirsky, Steven; MOORE, VIRGINIA - Cornell University; RYAN, MATTHEW - Cornell University; EHLKE, NANCY JO - University Of Minnesota; BARTOW, AMY - Natural Resources Conservation Service (NRCS, USDA); MONTEROS, MARIA - Bayer Crop Science; Hayes, Ryan; Kucek, Lisa

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2026
Publication Date: 8/16/2026
Citation: Tilhou, N.W., Riday, H., Vang, M., Mirsky, S.B., Moore, V., Ryan, M., Ehlke, N., Bartow, A., Monteros, M., Hayes, R.J., Kucek, L.K. 2026. Self-pollination rates in U.S. breeding populations of hairy vetch and smooth vetch. Crop Science. https://doi.org/10.1002/csc2.70353.
DOI: https://doi.org/10.1002/csc2.70353

Interpretive Summary: Plant breeders who are attempting to create improved varieties of the cover crops hairy vetch and smooth vetch need accurate estimates of the self-pollination rates for these species. Self-pollinated offpsring may have inbreeding depression, which will influence breeding decisions These vetches are typically out-crossing through insect pollination, but they are capable of seed prodution without insect exposure. Using low-cost molecular markers, this determined the frequency of self-pollination and cross-pollination across vetch parents and offspring in a breeding program. We observed an average self-pollination rate of 13%, but with a massive range (0-81%) that was not clearly connected to environmental conditions. In addition, we observed that self-pollinated offspring suffer from inbreeding depression (-48% plant biomass and -45% seed yield). This study will help inform future breeding decisions in hairy vetch and smooth vetch.

Technical Abstract: 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 towards out-crossing 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 U.S. breeding program using single sequence repeat markers. Self-pollination rates were determined using parents and progeny samples in 172 half-sib families (n=2,370 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%). Field-grown progeny had low self-pollination rates (4.8%) relative to greenhouse (27.6%) and breeding selection-derived 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 evolutionary role of mixed-mating.