Trichoderma harzianum T6776 modulates a complex metabolic network to stimulate tomato cv. Micro-Tom growth

Trichoderma harzianum 6776 is a novel and beneficial tomato fungal isolate. To investigate the mechanisms underlying the T. harzianum 6776-tomato interaction, several physiological and biochemical responses were explored on dwarf tomato plants, cv. Micro-Tom. Growth of treated and untreated plants was evaluated by measuring the height and biomass production of plants. The leaf pigment content and sugar partitioning in plant organs were evaluated by biochemical analysis. The photosynthetic parameters were measured by a miniaturized PAM fluorometer and a portable gas-exchange system. The hormonal analysis in root and xylem sap was performed by gas cromatography- mass spectrometry (GC-MS). T. harzianum 6776 positively affected plant growth, increasing the leaf pigment content and improving the photosynthetic activity at both stomatal and non-stomatal levels. Differences in pigment composition and photosynthetic performance were reflected in the carbohydrate content and their partitioning. In the absence of a pathogen, root and xylem vessel stress and growth-related hormone balance were affected by the interaction with T. harzianum 6776, with an increase in jasmonic and indoleacetic acids and a decrease in salicylic acid content. This study shows the complex connection between increased hormone accumulation and transport, altered sugar partitioning and enhanced photosynthetic efficiency induced by T. harzianum 6776, and how growth promotion is the result of the combination of these drastic changes in Micro-Tom plants.