Pollen genotyping by SABER-MassARRAY reveals that fewer than half of honey bee visits can cross-pollinate a self-incompatible crop.

Pollen limitation occurs when insufficient pollen or the wrong pollen genotype reaches the stigma. The pollination efficiency of flower visitors to crops has been investigated, but the genotypes of crop pollen carried have rarely been identified. We developed a method that detects SNPs in the pollen carried by single bees, using a customized single allele base extension reaction (SABER) with MassARRAY to distinguish genotypes that contribute only a small fraction to a mixed-genotype pollen sample. We used this method to identify the cultivars of pollen carried by honeybees at increasing distances from a cross-pollen source in two multi-cultivar macadamia orchards, one with wide single-cultivar blocks and one with narrow single-cultivar blocks. We found that many honeybees carried exclusively self-pollen. Only 30-53% of honeybees carried cross-pollen, representing the maximum that potentially contributes to crop production in self-incompatible crops. Distance from a cross-pollen source or the orchard design did not significantly affect the percentage of honeybees carrying cross-pollen. This study demonstrates significant potential to increase the effectiveness of honeybees as pollinators. Orchards can be re-designed to interplant cross-pollen sources and maximize the number of honeybees contributing to crop production. Improving pollination effectiveness will help to alleviate the growing shortfall in the supply of beehives required for crop pollination.