The ecology of autogamy in wild blueberry (Vaccinium angustifolium Aiton): Does the early clone get the bee?

Authors: DRUMMOND, FRANCIS - University Of Maine; Rowland, Lisa

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2020
Publication Date: 8/7/2020
Citation: Drummond, F.A., Rowland, L.J. 2020. The ecology of autogamy in wild blueberry (Vaccinium angustifolium Aiton): Does the early clone get the bee?. Agronomy. 10(8):1153. https://doi.org/10.3390/agronomy10081153.
DOI: https://doi.org/10.3390/agronomy10081153

Interpretive Summary: Lowbush blueberry production, which makes up about 1/4 of the total blueberry production in the U.S., is from intensively managed wild fields in Maine. Lowbush blueberry is considered an outcrossing crop with low levels of self-fertility (low levels of fruit set from self-pollinations). However, in previous studies, we have found that there are exceptions, with about 20-25% of plants exhibiting high levels of self-fertility. In this study, we identified lowbush blueberry plants that bloom early in the season, mid-season, and late in the season. We tested the hypothesis that we would find a higher percentage of self-fertile plants in the early blooming group, as these would have an evolutionary advantage when conditions are not favorable for pollination by bumble bees. We also measured bumble bee density in the fields across bloom times. Results indicated that the percentage of self-fertile plants was significantly higher in the early flowering group as opposed to the mid and late season groups. In addition, the density of bumble bees per plant was much higher early in the season, when flowers available for bee foraging are limited. This results in a high level of fruit set for these self-fertile plants. Because growers generally do not have honey bees delivered to their fields for pollinating until 25-30% of plants are in bloom, much of the early bloom contributions to yield are due to native bees. Thus, this information demonstrates the importance to growers of conserving and protecting wild bees on their farms.

Technical Abstract: Wild blueberry, Vaccinium angustifolium Aiton, is for the most part an obligate outcrossing species. However, there is a continuum across a gradient from zero to 100% in self-compatibility. We previously found by sampling many fields that 20-25% of clones during bloom have high levels of self-compatibility (> 50%). In 2009-2011, and 2015 we studied the ecology of self-pollination in wild blueberry, specifically its phenology and bee recruitment and subsequent bee density on bloom. We found that self-compatible clones were predominantly early blooming genotypes in the wild blueberry population. On average, fruit set and berry weight were highest in self-compatible genotypes. The bumble bee community (queens only early in the spring) was characterized by bees that spent large amounts of time foraging in self-compatible plant patches that comprised only a small proportion of the blueberry field, the highest density in the beginning of bloom when most genotypes in bloom were self-compatible. As bloom proceeded in the spring, more plants were in bloom and thus more land area was occupied by blooming plants. The absolute density of bumble bee queens per m2 declined, as a dilution effect, and this probably resulted in lower fruit set throughout the field.