Foliage Spraying Molybdenum Promotes Plant Growth and Controls Soilborne Ralstonia solanacearum in Different Tobacco Varieties

Tobacco growing is greatly threatened by the devastating bacterial wilt disease caused by soil-borne bacteria Ralstonia solanacearum (R. solanacearum). Balanced plant nutrition has become effective strategy for crop disease management. In this study, we firstly conducted greenhouse and field experiments to investigate the effects of Molybdenum (Mo), acting as a foliar fertilizer, on tobacco plant growth and bacterial wilt control. A susceptible variety (Yunyan 87) and a moderately resistant cultivar (Nanjiang 3) were used in this study. Under greenhouse condition, the results demonstrated that the disease incidence in the Mo-treated plants decreased to 41.7% (Yunyan 87) and 44.4% (Nanjiang 3) compared with that of non-Mo-treated plants. The control mechanisms are related to the reduced bacteria colonializations in tobacco and improvement of defense enzymes including peroxidase, catalase, superoxide dismutase, polyphenol oxidase and phenylalanine ammonialyase. Malondialdehyde levels halved after 200mg/L Mo treatment compared to the control group. The field experiment results also showed that supplements of 200mg/L Mo significantly decreased the disease incidence by 30.3% and 33.9%, respectively. Moreover, foliar application of Mo increased plant growth under both growth conditions, promoting leaf and root development. Mo was taken up by tobacco leaves, but the content decreased during the growth of plants. Mo application could provide an alternative strategy for efficient management of tobacco bacterial wilt, even in crops other than tobacco, especially in Modeficient planting regions, which would have a great impact on agriculture and favor sustainable agriculture development.