Activation of defense response in tomato against Fusarium wilt disease triggered by Trichoderma harzianum supplemented with exogenous chemical inducers (SA and MeJA)

The use of soil bioagent along with chemical inducers in controlling plant diseases is a unique strategy. The exogenous application of some chemical inducers such as salicylic acid (SA) or methyl jasmonate (MeJA) provides resistance to combat plant pathogens. The intrinsic mechanism that leads into the enhanced defense mechanism by using biological microorganisms, however, correlates with the signaling pathways involving these chemical inducers. In the present study, we have evaluated the biochemical changes relevant to defense activities when plants were pretreated with bioagent, Trichoderma harzianum (Th) and chemical inducers (SA and/or MeJA) and challenged by wilt pathogen Fusarium oxysporum f. sp . lycopersici. We have also evaluated the combined effect of biological (Th) and chemical inducers (SA and/or MeJA) pretreatment followed by pathogen exposure on the biochemical defense-related parameters in tomato. We found that the combined application of Trichoderma along with SA and MeJA provided a better strategy for controlling wilt pathogen rather than using bioagent and chemical inducers alone. The defense-related proteins and phenolics were found to be increased several folds at different time intervals following the combined treatment of biological and chemical inducers compared to when treatment was given alone with bioagent and chemical inducers. The activation of the phenylpropanoid pathway and accumulation of total phenolics were found to be highest at 48 h, whereas the activities of defense-related enzymes and PR proteins along with proline, were found to be maximum at 72 h. The activities of phenolics were also maximum at 48 h, and the activities of PR proteins and proline were higher at 72 h in all single treatments. However, the defense-related activities were greater in combined treatment compared to all single pretreated samples. Therefore, the combined pretreatment with bioagent and chemical inducers triggered the more aggressive defense responses when compared to single treatments and provided better protection against Fusarium wilt.