Indirect and direct benefits of the use of Trichoderma harzianum strain T-22 in agronomic plants subjected to abiotic and biotic stresses

Biological control of several plant diseases has been successfully achieved by the use of Trichoderma harzianum strain T-22, which acts through chemiotropic mycoparasitic interactions with the target fungal or bacterial organism. Since this strain can colonize the roots of most plant species across a wide range of soil types, it is particularly important for agronomic purposes. On the other hand, the study on the effect of T-22 or its derived substances against plant viruses (e.g. Cucumber mosaic virus – CMV) and the pathogenic and molecular aspects involved in this kind of three-way cross-talk between the plant, virus and antagonist are very little known. Besides the use of T-22 as a biocontrol agent, it has been reported that this fungus can also directly improve root growth and plant development in the absence of pathogens. Several mechanisms have been proposed for this, such as production of some unidentified growth-regulating compounds by the fungus, the increased availability of nutrients for plants and induction of certain root morphological changes. All these findings indicate the versatility through which T-22 can directly increase plant tolerance against abiotic stresses, such as drought, salinity and soils with low fertility. In spite of their theoretical and practical importance, the mechanisms responsible for the growth response due to the direct (growthpromoting) and indirect (antipathogenic) actions of T-22 in agronomic plants have not been investigated extensively. This chapter, based on the most significant and updated studies published in the last years by our research group, aims to contribute to a better understanding of the fundamental biochemical and physiological aspects of the antipathogenic and plant growth-promoting activities of T-22 on some economically important crops. This could promote a rational and non-empirical inclusion of this important fungal species into modern agricultural sustainable practices.