Endophytic infection alleviates biotic stress in sunflower through regulation of defence hormones, antioxidants and functional amino acids

Eco-friendly strategies pertinent to disease resistance in crops are desired for sustainable agriculture as they minimize chemical input into the agriculture industry. Fungal endophytes with phytohormones secreting capacity are well known for their plant growth promotion but have never been reported previously for their favourable role in plant resistance against pathogens. We studied the role of two fungal endophytes in promoting growth of sunflower (Helianthus annuus L.) and regulating hormone signalling networks involved in plant defence against fungal infection caused by Alternaria alternata. The two endophytic fungi (Penicillium citrinum LWL4 and Aspergillus terreus LWL5) promoted growth of sunflower and produced gibberellins (GA(1), GA(3), GA(4), GA(9), GA(12), and GA(20)), organic acids (malic, quinic and succinic acid) and siderophore. In A. alternata infected plants, the sole or combined treatment of P. citrinum and A. terreus markedly reduced disease incidence and reprogrammed the host plants to higher growth. The signalling of plant-defence hormones, such as salicylic acid and jasmonic acid fluctuated with the application of sole or combined endophytes in the diseased plants. The endophyte-association regulated oxidative stress responses by activating glutathione and polyphenol oxidase, and down-regulating catalase and peroxidase. In diseased plants, the endophytic-symbiosis rescued plant growth by the overwintering synthesis of free amino acids. In conclusion, the inoculation of endophytes reprogrammed plant growth during disease incidence by regulating the defence-linked responses of the host plant. Exploring endophytic symbiosis can help achieve sustainable agriculture in an eco-friendly way without using fungicides.