Field design can affect cross-pollination and crop yield in strawberry (Fragaria x ananassa D.)

Abstract

The distance travelled by pollinators between successive flower visits can affect the quality of pollen transferred among plants. In cropping environments, especially monoculture systems, pollinators that travel between plants or rows may increase cross-pollination and consequently crop yield. However, the most commonly utilized crop pollinator, Apis mellifera L., tends to forage consecutively on nearest-neighbouring plants within rows. The level of cross-pollination can be further restricted in crops that are propagated by cloning. When a clonal variety is planted over large areas, the potential for outcrossed pollen deposition could be limited, regardless of pollinator flight distances. To investigate how pollinator movement and varietal diversity interact to affect crop pollination, we conducted an experiment with wild and honey bees in single- and multiple-variety strawberry fields. We hypothesized that the amount of cross-pollination provided by wild bees in multiple-variety strawberry fields would be greater than in single-variety fields, and greater than that provided by honey bees in either field type. We found that, indeed, flowers visited by wild bees produced larger strawberries than those visited by honey bees in multiple-variety plots, but only in the more self-incompatible of the two strawberry varieties tested. Strawberries resulting from honey bee pollination were of similar size regardless of the number of varieties planted in the field. Our results show that certain multiple-variety strawberry fields can benefit from the irregular foraging patterns of some solitary bee species, leading to increased cross-pollination and crop yield. Strawberry growers could take advantage of this effect by planting multiple varieties in close proximity and by supporting wild bee populations on farms.