Location: Dairy Forage ResearchTitle: Seed-parent fecundity distributions in bee-pollinated forage legume polycrosses
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2016
Publication Date: 6/16/2017
Citation: Riday, H. 2017. Seed-parent fecundity distributions in bee-pollinated forage legume polycrosses. Crop Science. 57(3):1504-1510.
Interpretive Summary: Forage legume breeders are concerned about inbreeding during the breeding process, since inbreeding results in a reduction in performance of material created through breeding. In forage breeding, selected plants are group mated (termed polycross). Breeders avoid smaller numbers of plants in a polycrossing as this leads to increased inbreeding. This study presents a more accurate model of the expected amount of inbreeding based on the number of individuals in a polycross compared to models presented in the past. This study also shows that lower seed yielding polycrosses tend to have greater amounts of inbreeding. Forage breeders can use the models presented in this study in their research and breeding programs to better understand and minimize inbreeding. Based on this study, breeders could try to maximize polycross seed yield in order to minimize inbreeding.
Technical Abstract: Modeling expected fecundity distributions in bee-pollinated forage legume polycrosses allows more accurate assessment of effective polycross size and its inbreeding consequences. In this study, polycross size (N) standardized seed-parent fecundity frequencies [(Pfi – (1/N))/(1/N)] were modeled on 169 polycrosses in four species [alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), kura clover (Trifolium ambiguum Bieb.), and red clover (Trifolium pratense L.)] using Weibull distributions (scale parameter k and shape parameter lambda), specifically in the form of an inverse cumulative distribution function. Based on all polycrosses, it was determined that k could be predicted from lambda using a fifth order polynomial (k = 0.1019lambda5 - 0.9441lambda4 + 3.4386lambda3 - 6.2398lambda2 + 5.7585lambda - 1.0662, r² = 0.905, P < 0.0001). It was also determined that, across all polycrosses, lambda estimates were lognormally distributed (scale parameter ' = 0.154, shape parameter s = 0.340, r2 = 0.991). Polycross lambda estimates were not correlated with polycross size (N), however lambda estimates were linearly correlated with a polycross’ median seed plant-1 (lambda = 1.46 x 10-4[median seed plant-1] + 0.934, r² = 0.446, P < 0.0001). Linear model comparisons between alfalfa and red clover polycrosses showed that the two species had significantly different linear models (P = 0.032). The relationship between lambda estimates and median seed plant-1 is hypothesized to be the result of seed production in stressful environments resulting in lower median seed-parent fecundity and greater deviation from random mating in the form of larger lambda values. Polycross seed-parent fecundity lambda estimates were correlated with pollen-parent fecundity lambda estimates (r = 0.780, P = 0.022).