Disease management during bloom affects the floral microbiome but not pollination in a mass-flowering crop.
Abstract
Flowering crops are heavily managed during bloom to both promote pollination and prevent disease. Disease management practices can alter the floral microbiome, including pathogens and nontarget microbes. However, whether agrochemical presence or altered microbiome composition affect pollinator foraging and pollination services is unclear. We assessed effects of orchard management tactics and landscape context on the flower microbiome in almond, Prunus dulcis. Fourteen orchards (five conventional, four organic and five conventional with habitat augmentation) were sampled at early and peak bloom to characterize bacterial and fungal communities associated with floral tissues. The surveys were complemented by an artificial flower experiment to assess effects of fungicides and microbes on honey bee foraging. Finally, a field trial was conducted to test effects of fungicides and microbes on pollination. As bloom progressed, bacterial and fungal abundance and diversity increased across all floral tissue types and management strategies. The magnitude by which microbial abundance and diversity were affected varied, with proximity to apiaries and orchard management having notable effects on bacteria and fungi respectively. Experiments revealed that fungicides reduced nectar removal by honey bees; however, neither fungicide nor microbe treatments affected pollination, as measured through pollen tube initiation and growth. Synthesis and applications. Our results reveal that microbiota associated with flowers of a pollinator-dependent crop are temporally dynamic and sensitive to management practices. However, pollination services in almond may be resilient to both agrochemical disturbance and microbial augmentation of flowers, the latter of which may become more prominent as microbial solutions to disease management are embraced in agroecosystems.