Effectiveness of systemic resistance toward Aphis gossypii (Hom., Aphididae) as induced by combined applications of the endophytes Fusarium oxysporum Fo162 and Rhizobium etli G12

Abstract

The mutualistic root-colonizing endophytes Fusarium oxysporum strain Fo162 (Fo162) and Rhizobium etli strain G12 (G12) have been shown to individually induce systemic resistance against the sucking insect Aphis gossypii Glover (Hom., Aphididae). Simultaneous application of both organisms may be a strategy to further increase the systemic defense responses and thus the biocontrol efficacy. The simultaneous inoculation of both endophytes, either in a mixed or in a spatially-separated way, also reduced the aphid population in comparison to untreated squash plants. However, both types of combined treatments did not lead to significant additive biocontrol levels, i.e. further reduction in the aphid population, when compared to individual inoculation. A choice experiment with intact squash plants showed that the aphids favor feeding on endophyte-free plants, indicating that both Fo162 and G12 are able to affect the host plant preference by the aphids. The data illustrate that cocktail type inoculants comprising of different beneficial microorganisms may not always enhance the biocontrol efficacy against insects. Thus, although both Fo162 and G12 are recognized as biocontrol agents, their mutual interactions and their interactions with the host plant have to be taken into account in co-inoculation strategies in biocontrol.