Melatonin and fungal metabolites synergistically enhance tomato tolerance to Cd and disease resistance by regulating phytohormones

Abstract

Mitigating biotic and abiotic stresses of plants through natural products is an environmental friendly and chemical free approach. In this study, the synergistic effect of exogenous application of melatonin (MT) and fungal metabolites (FM) were evaluated for their mitigation affects against bacterial wilt disease and cadmium toxicity in tomato plants. By using a multi-faceted approach including phytohormonal profiling, quantitative real-time PCR, biochemical assays, antibacterial test, and cadmium (Cd) content evaluation in plants, we presented evidence that MT and FM augmented disease resistance, tolerance to Cd toxicity and the combined treatment caused significantly increased effect by regulating phytohormone expression. Transcription of the genes related to the jasmonic acid (JA) and salicylic acid (SA) were enhanced while genes related to ethylene (ET) were decreased, which caused an increased JA and SA content and decrease in ET level. The plants treated with MT and FM showed significant reduction in disease intensity and Cd content compared to the control. Moreover, analyses indicated that the application of MT and FM reduced oxidative damage and increased antioxidant enzymes activity. The increased synergistic impact of MT and FM is supposed to be due to blending action mechanisms like resistance induction and enhanced growth impact of MT and antibacterial action of FM against R. solanacearum. These research findings emphasize the efficacy of a sustainable and comprehensive strategy in controlling bacterial wilt and Cd toxicity in tomato plants.