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Bacterial populations on the surfaces of organic and conventionally grown almond drupes

J.A. McGarvey, R. Han, J.H. Connell, L.H. Stanker, R. Hnasko
Journal of applied microbiology 2015 v.119 no.2 pp. 529-538
Actinobacteria, RNA libraries, almonds, alpha-Proteobacteria, bacteria, consumer preferences, gamma-Proteobacteria, hulling, hulls, organic production, phyllosphere, ribosomal RNA, stone fruits
AIMS: To compare the bacterial populations on organically and conventionally grown almond drupes before and after hull split. METHODS AND RESULTS: We constructed 16S rRNA gene libraries, containing approx. 3000 sequences each, from the bacteria from organically and conventionally grown drupes before and after hull split. We observed that before hull split both conventionally and organically grown drupes were colonized by relatively few types of bacteria that were mostly common phyllosphere‐associated Proteobacteria. However, the organically grown drupes contained significantly more Alphaproteobacteria and the conventionally grown drupes contained significantly more Gammaproteobacteria. The conventionally grown drupes also contained significantly more sequences associated with the phylum Actinobacteria. After hull split, we observed a significant increase in bacterial diversity, with many newly appearing sequences that were not normally associated with the phyllosphere. CONCLUSIONS: Organic and conventional growing methodologies influence the types of bacteria on almond drupes and hull split results in a burst of microbial diversification. SIGNIFICANCE AND IMPACT OF THE STUDY: Production of organic produce is increasing due to consumer preferences, but it was unknown how this methodology affects the bacterial populations on almond drupes. This is the first study to compare the bacterial populations of organically and conventionally grown almond drupes.