Abstract
Production of many agricultural crops and fruits strongly depends on pollinators. For instance, pome fruits such as apple and pear are highly dependent on pollination for fruit set, fruit quality, and yield. Nectar is often inhabited by microbes, most often yeasts and bacteria, which may change nectar quality and therefore also affect plant–pollinator interactions. Here, we used high‐throughput 16S ribosomal RNA gene amplicon sequencing to investigate the temporal and spatial variation in bacterial communities in floral nectar of apple and pear. We sampled 15 apple (Malus x domestica Borkh.) and 15 pear (Pyrus communis L.) orchards distributed over the eastern part of Belgium over a timespan of seven days. Nectar bacterial community composition differed strongly among fruit species. Nectar of pear was dominated by Actinobacteria, followed by Proteobacteria and Firmicutes. Apple nectar was strongly enriched in Bacteroidetes, a phylum which until now has been found to be rarely associated with floral nectar. Nectar was dominated by only a few bacterial species, with Brevibacterium (Actinobacteria) and Undibacterium (Proteobacteria) as the most abundant bacteria in pear and apple nectar, respectively. Bacterial richness and diversity were found to fluctuate during flowering, likely due to changing environmental conditions. Additionally, spatial structure in nectar bacterial community composition was found in apple orchards, while this was not the case for pear. Differences in nectar bacterial communities between apple and pear nectar may differently affect the chemical and nutritional composition of the nectar, influencing pollinator attraction and visitation, and thus pollination efficacy in general.
Highlights
Production of most agricultural crops and fruits strongly depends on bees or other animals for pollination (Klein et al, 2007), an ecosys‐ tem service strongly influenced by floral nectar and pollen (Knauer & Schiestl, 2015; Somme et al, 2015)
Recent surveys have shown that nectar is often inhabited by microorganisms, most often yeasts and bacteria, which may change nectar quality and affect plant–pollinator interactions
Nectar bacteria belong to a limited set of phyla, including Actinobacteria, Firmicutes, and Proteobacteria (Pozo et al, 2015), in some nectars Bacteroidetes were found (Fridman et al, 2012)
Summary
Production of most agricultural crops and fruits strongly depends on bees or other animals for pollination (Klein et al, 2007), an ecosys‐ tem service strongly influenced by floral nectar and pollen (Knauer & Schiestl, 2015; Somme et al, 2015). It has been found that microbial communities of floral nectar may differ among plant species (Pozo et al, 2015), populations of the same spe‐ cies (Jacquemyn, Lenaerts, Brys, et al, 2013), or even among different flowers of the same plant (Canto & Herrera, 2012), suggesting that plant features and local or temporal conditions affect the community composition. A few studies have investigated the flowers from apple and pear for microbial presence, often in relation to the fire blight‐causing pathogen Erwinia amylovora (Pusey et al, 2009; Shade, McManus, & Handelsman, 2013), no study so far fo‐ cused on the microorganisms inhabiting their nectar. We addressed the following research questions: (a) Does the bacterial community composition of floral nectar of “Jonagold” apple and “Conference” pear differ among each other; (b) does the nectar bacterial commu‐ nity composition change during the flowering period; (c) are these temporal changes in nectar bacterial community composition fruit species dependent; and (d) is similarity in the nectar bacterial com‐ munities among different orchards related to geographical distance? Apart from new fundamental insights, our study provides basic in‐ formation that can pave the way for specific manipulations to in‐ crease pollinator attraction and improve the pollination process
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