Today we are continuing our story of ornamental apples (crabapples). Plants are living in a microbial world. They interact not only with microbes in the soil but also the ones living in their flowers. These microbial partners can be beneficial or harmful, and thus hold the key for plant disease resistance and health. Our research aims to understand the factors that determine which microbes and how many of them are in flowers (i.e. flower microbiome).

One important factor that we focus on is plant–pollinator interactions. When pollinators visit flowers, they not only collect pollen and nectar, but they also drink microbes in the nectar, pick up microbes on petals or pollen, and deposit microbes from their own bodies. Thus, which pollinators and how many pollinators visit flowers influence the flower microbiome.

Undergraduate researchers, Miyauna Incarnato and Eve Kaufman working with Dr. Na Wei, surveyed pollinators that visited crabapples at the Holden Arboretum. At Holden, there are 40 different crabapple cultivars, and each cultivar has multiple trees. These cultivars vary a lot in their flower color, size and smell, and attract many pollinators during blooming in late April and May.

Our research group conducted pollinator observations for each crabapple tree. We identified a number of pollinator species and groups: honey bees (Apis mellifera), bumble bees (Bombus bimaculatus, Bombus griseocollis, and Bombus impatiens), carpenter bees (Xylocopa virginica), Andrenidae (mining bees), Halictidae (green metallic bees), Colletidae (plasterer bees), Megachilidae (small black bees) wasps, flies, and butterflies. Based on the field observations, we built a plant–pollinator interaction network (pollinator icons by Cameron Squire). We found that crabapple cultivars varied in their visiting pollinators. Our next step is to link plant–pollinator interactions to flower microbiome in crabapples.