Effects of biocontrol agents and compost against the Phytophthora capsici of zucchini and their impact on the rhizosphere microbiota

Four different biocontrol agents (BCAs) and two composts have been used in this study to evaluate their efficiency against the Phytophthora blight of zucchini caused by Phytophthora capsici. The effects of the BCAs and composts on the microbiota of the zucchini rhizosphere were examined at the end of experimental trials conducted in 2016 and 2017 on two farms in natural and artificially infested soils. The next generation amplicon sequencing technology and quantitative Polymerase Chain Reaction - qPCR were used as targeted and untargeted approaches, respectively. The abundance of P. capsici, as measured for all the treatments over both years, decreased with respect to the untreated control, and it may be assumed that a direct pathogen-beneficial microorganism interaction occurred. All the treatments reduced the disease incidence by at least 50% in both sites in naturally or artificially infested soil and in at both sampling periods. The disease index reflected the pathogen abundance. The development of microbiota and mycobiota was not affected by the BCAs, thus indicating that the tested treatments did not interact negatively with the microbial communities, which in turn suggested a slow but good adaptation of the biocontrol agents to the environment. The combination of targeted and untargeted approaches may help to understand the effects of different BCAs on the development of Phytophthora capsici.