Embryonic genetic load for a neotropical conifer, Pinus patula Schiede et Deppe

Genetic loads tend to be higher for widely distributed boreal and temperate pines compared to other plants and most animals. Although genetic loads have not been estimated for neotropical pines, it seems likely that genetic loads will be lower due to disjunct population structure and high rates of endemism. Embryonic genetic load is reported for a founder population of Pinus patula, a neotropical species used as a Zimbabwe exotic. The study was based on a novel orthogonal inbred mating design with 5 grandparents and 12 parents equally represented at four levels of inbreeding. Contrary to predictions, P. patula had an average of six to eight embryonic lethal equivalents, a genetic load comparable to temperate and boreal pines. Embryo viability declined linearly with increased inbreeding levels (F = 0-0.5), supporting the independent lethal model. P. patula appears to have a stable embryo-lethal system despite small population sizes.