A TaqMan-based qPCR assay for quantitative detection of the biocontrol agents Bacillus subtilis strain QST713 and Bacillus amyloliquefaciens subsp. plantarum strain D747

Biological control agents (BCAs) play an important role in crop protection. They can improve sustainability, prevent resistance to fungicides in target pathogens and reduce fungicide residues on produce. Bacillus subtilis strain QST713 (Serenade Max; Bayer CropScience, Leverkusen, Germany) and Bacillus amyloliquefaciens subsp. plantarum strain D747 [Amylo-X; CBC Europe S.r.l.—Biogard Division, Nova Milanese (MB), Italy] are two commercially available BCAs that are used against grey mould on table grape and other crops. TaqMan-based quantitative (q)PCR assays were developed and validated for quantitative and specific detection of the two BCAs on grape bunches following field sprays. Specific molecular markers were developed for each BCA, and TaqMan probes were designed and tested in qPCR on DNA extracted from washing water of grape berries. The assay proved specific and sensitive for both BCAs allowing detection at density as low as three colony-forming units (CFU) per gram of berries. The method will be useful to investigate the population dynamics of the two BCAs following their applications in vineyards.