Evaluation of Resistance-Inducing Compounds for Management of Tomato Bacterial Speck in Jos, Plateau State

Bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, is an economically significant disease in highland tomato production systems such as those on the Jos Plateau, where cool moist conditions favour its development. Systemic acquired resistance inducers offer a targeted and environmentally acceptable approach to enhancing plant defences against bacterial pathogens. This study evaluated the efficacy of four resistance-inducing compounds, including acibenzolar-S-methyl, salicylic acid, beta-aminobutyric acid, and a commercial chitosan formulation, for management of bacterial speck on tomato under Jos Plateau field conditions. Trials conducted at the Plateau State University experimental farm over two seasons used a randomised complete block design, with bacterial speck incidence, marker enzyme activities (phenylalanine ammonia lyase, peroxidase), and marketable fruit yield as measured outcomes. Acibenzolar-S-methyl treatment at 50 mg per litre applied at transplanting and 14 days post-transplanting reduced bacterial speck incidence by 67 percent and was associated with the highest phenylalanine ammonia lyase and peroxidase activities in treated leaf tissue. Chitosan treatment provided moderate disease suppression of 43 percent, comparable to one-third of the copper bactericide standard. Beta-aminobutyric acid showed inconsistent results between seasons. Induced resistance treatments were most effective when applied preventively before pathogen challenge, confirming their protective rather than curative mode of action. The study recommends acibenzolar-S-methyl as a viable resistance management option for highland tomato producers. Keywords: bacterial speck, Pseudomonas syringae, induced resistance, tomato, Plateau State.