Understanding the Interactions Between Pollen-Borne Ilarviruses and Pollinators in Peach Orchards

Pollen-mediated virus transmission is a common problem in fruit crops. Prunus necrotic ringspot virus (PNRSV) and prune dwarf virus (PDV) are pollen-borne ilarviruses endemic to the southeastern U.S. and cause substantial losses in peach production. PNRSV and PDV are primarily transmitted through vegetative propagation (grafting) as well as via pollen and seed. However, the role of pollinators in transmission dynamics of these viruses is not well understood. First, I documented the bee diversity and abundance during peach bloom in South Carolina, identifying Bombus and Apis as the most dominant genera, followed by Eucera, Andrena and Habropoda. Bee community composition varied over the peach bloom period, with Apis dominating early bloom, while Bombus and Andrena were most abundant during late bloom. Next, I investigated if bees and thrips contribute to PNRSV and PDV spread in peach orchards. A two-year survey of peach orchards demonstrated that both bees and thrips carry PNRSV and PDV-positive pollen during bloom and move along orchard blocks, potentially facilitating virus spread. Since PNRSV has been found in wild Prunus spp. at orchard borders, I used high-throughput sequencing (HTS) to track the foraging history of bees, assessing whether they serve as a bridge for the movement of virus-infected pollen between cultivated peaches and wild species. Findings revealed that bees visit a wide range of plant taxa, including wild Prunusspecies such as Prunus serotina and P. caroliniana, and there was a significant association between the presence of wild Prunus spp. and detection of PNRSV in bee-collected pollen samples. I also examined the effects of PNRSV and PDV infection on pollen health (i.e., morphology, viability and germination) and found that PNRSV had cultivar-specific effects on pollen health whereas PDV infection affected pollen width and reduced pollen viability but did not affect pollen germination. Future research should explore the effects of ilarvirus infection on interactions between plants and pollinators to better understand transmission ecology of these viruses. Insights into the ecology and transmission dynamics of pollen-borne ilarviruses are crucial for informing future disease management strategies to improve orchard health.