Rhizobial elicitor molecule signaling muskmelon defense against gummy stem blight disease involving innate immune response

Abstract

The crude oligosaccharide (CO) from plant growth-promoting fungus, Talaromyces verruculosum (AB2 strain) was isolated from the muskmelon rhizospheric soil in this study. Various concentrations of CO elicitor was utilized for seed treatment to muskmelon at varying time intervals to evaluate its plant growth promotion and disease protection ability against gummy stem blight disease, which is caused by Stagonosporopsis cucurbitacearum (DBTNP-2 strain). A maximum of 92% of germination and seedling vigor of 2439.76 was recorded at 6 h under in vitro conditions, after CO-pre-treated plants with 4 mgml−1. Similarly, when compared to the control, the CO-treated seed (4 mgml−1) exhibited increased vegetative growth parameters under greenhouse conditions after 6 h. In the studies of disease protection, a significant 80.88% protection from disease was noticed in plants pre-treated with CO (4 mgml−1) after 6 h. The protection thus obtained was systemic and needed a minimal of five days to achieve maximum resistance and thereafter, this protection remained stable at all time periods. An early elevated hypersensitive reaction and the defense related cellular components such as lignin, callose, H2O2 and phenol deposition, were noticed in comparison with the unprocessed control plants. Furthermore, when compared to pathogen or water control, a significant up-regulation of defense-related PAL, POX, PPO and LOX enzymes was found in the plants, which were pre-treated with CO, either with or without pathogen infection. The present research directly evidences that when confronted with the pathogen infection, the CO-treated muskmelon plants promote plant growth and trigger the resistance through the morphological, histological and biochemical defense mechanisms.