Disease management during bloom affects the floral microbiome but not pollination in a mass-flowering crop

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 non-target microbes.
However, whether agrochemical presence or altered microbiome composition
affect pollinator foraging and pollination services is unclear. We
assessed the effects of orchard management tactics and landscape context
on the flower microbiome in almond, Prunus dulcis. Fourteen orchards (5
conventional, 4 organic, 5 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 the effects of
fungicides and microbes on honey bee foraging. Finally, a field trial was
conducted to test the 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 almonds 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.