The effect of Trichoderma harzianum in mitigating low temperature stress in tomato (Solanum lycopersicum L.) plants

Most tomato cultivars are considered as chilling-sensitive plants and the chilling stress prevalent in many regions of the northern hemisphere limits their culture. Some plant-symbiotic strains of the genus Trichoderma colonize plant roots and induce significant changes in plant gene expression leading to enhanced growth, especially under biotic and abiotic stresses. In this study, the effects of Trichoderma harzianurn AK20G strain (Th), as a bio-control agent, was investigated on the tolerance of tomato (Solarium lycopersicum L.) plants under chilling stress. Tomato plants were exposed to low temperatures after being inoculated with "Th" and their physiological, biochemical and molecular responses were investigated at different time courses. Results showed that "Th" have efficiently alleviated the adverse effects of cold stress leading to enhanced photosynthetic and growth rates. It was also revealed that "Th" reduced the lipid peroxidation rate and electrolyte leakage while increasing leaf water content and proline accumulation. Gene expression analysis revealed that the expression of transcription factor NAC1 and dehydrin TAS14 was drastically surged after cold treatment while P5CS expression was decreased with continuation of the cold stress. Interestingly, "Th" improved the expression of TAS14 and P5CS and their expression increased with the time during the experiment. The findings of the present study provide a detailed insight into the physio-biochemical and molecular processes leading to low temperature tolerance in T. harzianwn-inoculated tomato plants.