Variation in Male Fertilities and Pairwise Mating Probabilities in Picea glauca

Frequencies of multilocus male gametes in seeds collected from clones in several blocks of a white spruce seed orchard were analyzed as part of a 2-yr study of mating system variation in this species. Observed frequencies of male gamete types departed significantly from those expected assuming equal male fertilities among clones. Male gamete frequencies in seed crops were significantly heterogeneous among clones within blocks, and among blocks within clones. Clonal male fertilities were estimated from male gamete frequency data. These estimates were highly skewed, with a small proportion of the clones contributing male gametes to the majority of the seed. The estimates were significantly heterogeneous among clones within blocks, and among blocks within clones. Between-year variation in clonal male fertilities was also pronounced, with male fertilities of some clones changing by as much as three orders of magnitude. Clonal male fertility was significantly correlated with clonal male cone production in both years. These results are important with regard to assumptions made for the estimation of general combining ability, average genetic correlation among progeny from single parents, and expected response to selection in open-pollinated plant populations.