Environmental stress responses of the Bacillus amyloliquefaciens CPA-8-formulated products on nectarines and peaches

The biocontrol agent Bacillus amyloliquefaciens CPA-8 has been suggested as an effective alternative to chemical applications against brown rot caused by Monilinia spp. This study aimed to describe the population dynamics of CPA-8 on the surface of nectarines and peaches after being exposed to unfavourable environmental conditions. Two CPA-8-formulated products were obtained by fluid-bed spray-drying and then applied on fruit. Although both products included 20% sucrose plus 10% skimmed milk as protecting agents, they differ in the carrier material used during the formulation process: maltodextrin (CPA-8-formulated product called BA3) or potato starch (CPA-8-formulated product called BA4). CPA-8 has demonstrated wide tolerance to different factors such as, temperature, relative humidity and simulated rainfall. The minimal antagonist population obtained after exposure was generally higher than 104 CFU cm−2 of fruit surface, which ensures high treatment coverture and therefore, efficacy. The results also indicated that peaches were, in general, more suitable for the CPA-8 survival than nectarines. Moreover, the properties of the two CPA-8-formulated products influenced the population dynamics of the bacterium, suggesting that the BA4 CPA-8-formulated product provided higher degree of ecological fitness of CPA-8 over the fruit than the BA3 CPA-8-formulated product. The data obtained in this work led us to conclude that the integration of these CPA-8-formulated products into cropping systems is a promising strategy to achieve higher levels of brown rot control and hence contribute to a successful handling of postharvest diseases in stone fruit.

This research was supported by the European project BIOCOMES FP7-612713 and by the Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya for the PhD grant 2014-FI-B00367 (Amparo M. Gotor Vila). The authors also thank CERCA Program (Generalitat de Catalunya) and the technical and logistical support provided by Cristina Solsona, Cèlia Sánchez and Andrea Berge.