Functional diversity of biocontrol communities as a tool to build consortia and improve their control efficacy

This study contributes to the improvement of biocontrol strategies, in particular, to develop biological formulations based on microbial consortia. The competitive ability of a microbial species within a consortium is influenced by several factors, such as growth and sporulation rates, niche overlap and interactions with environmental conditions. New strains of Penicillium rubens, P. frequentans and Epicoccum nigrum were isolated from various areas and times of the year. The in vitro effect of temperature and pH on growth and sporulation of each potential antagonist, its metabolism and biocontrol efficacy were evaluated and compared to the reference strains previously identified as biocontrol agents: P. rubens (PO212), P. frequentans (Pf909) and E. nigrum (EPI282). All of the isolates exhibited better growth and sporulation rates at 22°C than at 10°C, for P. rubens and P. frequentans isolates at pH 5.5 but for E. nigrum isolates at pH 8. Only some isolates of P. rubens maintained this maximum sporulation level at pH 8 and 22°C, being significantly higher than the reference strain PO212 under these conditions. Some isolates outperformed the reference strain EPI282 in growth at 22 and 10°C, and pH 5.5 and pH 8. No isolate exhibited better growth and sporulation than Pf909 at both pH and temperature levels, nor better sporulation than EPI282. Ten isolates of P. rubens controlled tomato wilt, but only five of them showed a significantly higher level compared to the reference strain PO212. Only three isolates of these had a niche overlap index (NOI) lower than 0.9 with the tested compounds, indicating that these three P. rubens isolates could have a sufficiently different ecological niche from PO212, and that the other six could compete with PO212; to benefit from their higher control ability, they had to be used individually. Ten isolates of P. frequentans showed a similar level of disease control compared to the reference strain Pf909, and two of them had a NOI of <0.9 with almost the carbohydrate, amine and amino acids tested, indicating that both might have an ecological niche sufficiently different from Pf909. Among the 17 new isolates of E. nigrum able to control cherry rot, only five of them showed a significantly higher level compared to the reference strain EPI282, but only four of them had a NOI of <0.9 with almost one of the tested compounds. The ability to establish and maintain populations of biocontrol agents and the potential of including new isolates in consortia to improve biocontrol were discussed.