Antimicrobial Activity of Foliar Fertilizer Formulations and their Effect on Ice Nucleation Activity of Pseudomonas syringae Pv. garcae Van Hall; the Causal Agent of Bacterial Blight of Coffee

Abstract

This study was carried out with the broad objective of assessing the potential for control of Bacterial Blight of Coffee (BBC) using foliar fertilizer applications to Inhibit Ice Nucleation Activity (INA) of the causative agent (Pseudomonas syringae pv. garcae). Bacteria isolates from four coffee growing areas in Kenya were characterized based on visual, biochemical, physiological and pathogenicity characteristics to distinguish the pathogenic isolates of P. syringae from other phylloplane epiphytic bacteria. Isolates of bacteria from diseased coffee plants were categorised in three groups. Isolates that were pathogenic to coffee and produced typical symptoms of BBC fell under group 1 and were assumed to be of P. syringae pv. garcae. Other isolates that fell under groups 2 and 3 were considered to be saprophytic epiphytes. Four commercially available fertilizer formulations; Bayfolan™, Mboleasafi™, Farmphoska™ and Farmfoliar™ were tested on four pathogenic bacteria isolates collected from the four regions. All formulations significantly (p<0.05) reduced the number of bacterial colony forming units. Bayfolan™ treatment had the highest bacterial growth inhibition potential while Farmfoliar™ was least inhibitive. All the isolates were Ice Nucleation Active (INA+) and all the fertilizer formulations were potentially capable of suppressing the bacterial ice nucleation activity with Farmphoska™ being the most suppressive. Findings presented in this report indicate a potential for the management of BBC using foliar fertilizers to suppress the bacterial INA.