Mating systems and pollination biology of velvet mesquite (Prosopis velutina Wooten)

Little is known of the genetics of multipurpose trees in the genus Prosopis. These studies, which examined mating systems and pollination biology of P. velutina Wooten, improved our understanding of genetic structure and gene flow in natural and artificial populations.; There was no evidence for either male or female sterility, but early and later flowering trees could be functionally male and female, respectively. Pollen loads on stigmas of mature flowers were adequate for pod production, so low fruit:flower ratios in P. velutina were not attributed to inadequate pollination. Flowers were receptive to pollen prior to complete anthesis when only stigmas were exserted, a trait that will facilitate controlled pollination.; Hand pollinations demonstrated that P. velutina was self-fertile. Lower pod production in selfs compared to outcrosses was attributed to genetic load. Multilocus estimates of mating systems parameters derived from data for 3 isozyme systems of 30 open-pollinated families revealed 20.7% selfing and 7.1% biparental inbreeding in mating in three natural populations. Implications of self-fertility and inbreeding were discussed in relation to breeding programs, and natural and artificial populations. Genetic subdivision was found within these populations, but not among them. This genetic structure was attributed to initial long-distance seed dispersal into grasslands by livestock, followed by short-distance seed dispersal from "nucleus" trees by livestock and wildlife.; Twenty-six genera of insects foraged on the flowers. Small insects were effective pollinators of P. velutina, but nocturnal insects were not. The most efficient pollinators, based on pod production after single visits to inflorescences, were native leafcutter bees (Megachilidae), followed by Perdita spp., Apis mellifera, and Volucella spp. Insect behavior can affect plant mating systems by altering the relative amounts of selfing and outcrossing, and as pollinator guilds change through the flowering season. It was also found that individual trees can bear up to three cohorts of flowers during a growing season. These factors combine to make the mating systems of P. velutina more complicated than previously thought. Approaches for using insects in breeding and seed orchards were discussed.