The research describes the estimation of the outcrossing rate in Stylosanthes capitata and Stylosanthes guianensis, two important forage legumes for tropical areas. Previously, the only available estimates of their outcrossing rates were based on morphological markers, and the genus was considered primarily self-pollinated. The study used microsatellite markers to estimate the outcrossing rates in open-pollinated populations of these species.

The multi locus outcrossing rate for S. capitata was estimated using 10 polymorphic loci, whereas five microsatellites were used for S. guianensis. The multi locus outcrossing rates for S. capitata and S. guianensis were 31% and 26%, respectively, suggesting a mixed mating system with predominance of autogamy (self-fertilization).

The study found little inbreeding other than selfing. The estimated Wright’s fixation index of the parental generation was lower than expected based on the multi locus outcrossing rate, possibly due to the use of some heterozygous breeding genotypes for the study.