Molecular tools applied to identify and quantify the biocontrol agent Pantoea agglomerans CPA-2 in postharvest treatments on oranges

Abstract

Pantoea agglomerans strain CPA-2 is an effective biocontrol agent (BCA) for postharvest diseases of citrus and pome fruit. To implement their use as a control strategy is necessary to study the traceability of BCAs in the environment during application, for registration issues. In this study, the presence and persistence of CPA-2 was monitored in the packing line, storage chambers and on working clothes by conventional PCR. After postharvest application, the presence of CPA-2 was not detectable in the environment and storage chambers, whereas on working clothes and the packing line its persistence was less than 1 and 3 days, respectively. Additionally, the CPA-2 population was quantified on oranges stored at two different temperatures (20°C and 4°C) by quantitative PCR (qPCR), sample pretreatment with a propidium monizade dye (PMA–qPCR) and the dilution plating method. At the initial time of the assay, no differences were observed in CPA-2 populations quantified by qPCR, PMA–qPCR, and dilution plating, at both storage temperatures. However, CPA-2 populations quantified by PMA–qPCR were significantly different compared with those obtained by qPCR during the time-course of the assay; no significant differences were observed between PMA–qPCR and dilution plating. In conclusion, the persistence of P. agglomerans CPA-2 at different sampling areas after postharvest application was low. Furthermore, PMA–qPCR gave valuable information on viable population behavior and the presence of residual DNA from dead cells. In general, these studies help to understand the persistence of antagonists when applied under postharvest conditions and will lead to optimization of time and mode of application.