Improving Biological Control by Combining Biocontrol Agents Each with Several Mechanisms of Disease Suppression

Abstract

Two biocontrol agents, a yeast (Pichia guilermondii) and a bacterium (Bacillus mycoides), were tested separately and together for suppression of Botrytis cinerea on strawberry leaves and plants. Scanning electron microscopy revealed significant inhibition of Botrytis cinerea conidial germination in the presence of Pichia guilermondii, whereas Bacillus mycoides caused breakage and destruction of conidia. When both biocontrol agents were applied in a mixture, conidial destruction was more severe. The modes of action of each of the biocontrol agents were elucidated and the relative quantitative contribution of each mechanism to suppression of Botrytis cinerea was estimated using multiple regression with dummy variables. The improvement in control efficacy achieved by introducing one or more mechanisms at a time was calculated. Pichia guilermondii competed with Botrytis cinerea for glucose, sucrose, adenine, histidine, and folic acid. Viability of the yeast cells played a crucial role in suppression of Botrytis cinerea and they secreted an inhibitory compound that had an acropetal effect and was not volatile. Bacillus mycoides did not compete for any of the sugars, amino acids, or vitamins examined at a level that would affect Botrytis cinerea development. Viable cells and the compounds secreted by them contributed similarly to Botrytis cinerea suppression. The bacteria secreted volatile and non-volatile inhibitory compounds and activated the defense systems of the host. The nonvolatile compounds had both acropetal and basipetal effects. Mixture of Pichia guilermondii and Bacillus mycoides resulted in additive activity compared with their separate application. The combined activity was due to the summation of biocontrol mechanisms of both agents. This work provides a theoretical explanation for our previous findings of reduced disease control variability with a mixture of Pichia guilermondii and Bacillus mycoides.

Pythium oligandrum: an example of opportunistic success

“…In the last few years, several reports have shown that co-inoculation of beneficial microorganisms could stimulate plant growth and/or increase plant disease resistance relative to inoculation with a single biocontrol agent (Raimam et al, 2007;Whipps, 2004). Although such combinations may enhance the level of plant protection against pathogen attack (Ezziyyani et al, 2007;Guetsky et al, 2001Guetsky et al, , 2002, the possible competitiveness between these micro-organisms has to be taken into consideration (Alabouvette et al, 2006). …”

In vitro and in situ study of postharvest apple blue mold biocontrol by Aureobasidium pullulans: Evidence for the involvement of competition for nutrients

“…Although several possible mechanisms have been reported (Droby and Chalutz, 1994;Janisiewicz and Korsten, 2002;Massart and Jijakli, 2007), the main mode of action of yeast(-like) biocontrol agents is believed to be competition for nutrients and space (Droby and Chalutz, 1994;Lima et al, 1997;Janisiewicz et al, 2000;Castoria et al, 2001). According to the literature dealing with competition for nutrients and space using different antagonist/pathogen(/host) systems (Castoria et al, 1997(Castoria et al, , 2001Lima et al, 1997;Janisiewicz et al, 2000;Guetsky et al, 2002;Vero et al, 2002): (i) most studies have considered either the in vitro or the in situ approach but not both, (ii) the contribution of the competition for nutrients and competition for space has rarely been considered separately, and (iii) in situ assays have been often performed using the Nutrient Yeast Dextrose Broth medium whose composition is not comparable with that of host tissues. In the present study, competition for nutrients as a mode of action of A. pullulans strain Ach1-1 against P. expansum was first examined in vitro using a system that allows discrimination between competition for nutrients and that for space (Janisiewicz et al, 2000) using increasing concentrations of apple juice.…”

Biological control of tomato bacterial spot by seed microbiolization

“…The stability of the control by the microorganism is usually associated with the performance of multiple mechanisms of action (Guetsky et al, 2001) and with an aggressive colonization of the tissues of the host plant (Kloepper & Beauchamp, 1992). In the present study, the mechanisms of action of the DFs1420 isolate were not studied here but some of its capabilities are already known.…”