Bioactive Natural Products from Monarda for Control of Tomato Disease

Environmentally-friendly methods to control plant disease are needed in order to reach the goal of sustainability in agriculture. Because diseases caused by soil-borne organisms significantly reduce crop yields, identifying environmentally friendly methods for control of these diseases is imperative. The purpose of the research described in this thesis was to determine the impact of bioactive natural products on disease control in tomato production. The specific objectives were: 1) to determine the effect of adding herbage (dried and ground leaves and flowers) of three Monarda cultivars to greenhouse growth media on seedling losses caused by Rhizoctonia solani, and 2) to evaluate biological pesticides (alone and in various combinations) for control of Pythium disease. Experiments were designed as factorials with two rates of herbage, 0 or 10% (v/v) and two rates of R. solani inoculum, 0 or 2% (v/v) with 20 replicates in a randomized complete block design. In a second set of experiments, seedlings were transplanted into a substrate-based hydroponic system, and commercial production methods were used. The impact of herbage from three Monarda cultivars, one isolate of a commercial plant growth promoting rhizobacteria preparation, and one isolate of the pathogen Pythium myriotylum (all of which were substrate additives), as well as two isolates of Beauveria bassiana (seed treatment), alone and in combination was tested. Amending germination mix with herbage from 'Marshall's Delight' increased seedling height and germination above that of control regardless of R. solani infestation. Amendment with 'Sioux' did not protect against R. solani. In experiments with P. myriotylum, the pathogen rarely impacted fruit quantity or weight. Herbage did not increase fruit yield over nontreated controls, and treatment with B. bassiana reduced yield. However, there were significant interactions among treatments; for example Grade 1 tomatoes, treatment with P. myriotylium and B. Bassiana increased yield above that of treatments with P. myriotylium alone. Neither treatment was greater than control. Although additional research is needed, based on these results, these environmentally-friendly methods hold promise for disease control in tomatoes.