LAUSR

Halo blight caused by Pseudomonas syringae pv. phaseolicola is one of the major bacterial diseases on snap bean in Florida, and the outbreaks of this disease have occurred more often in recent years. Current management of this disease primarily depends on application of fixed copper-based bactericides, but the climate change and resistance development in the pathogen populations still cause hardship for disease management especially in south Florida. In this study, nicotinamide adenine dinucleotide (NAD+) was evaluated for its potential to reduce halo blight on snap bean. When NAD+ at 5 mM was applied by soil drench, foliar spray, or leaf infiltration, NAD+ significantly (P < 0.05) reduced disease severity of halo blight on snap bean compared to the untreated control. When NAD+ was applied by leaf infiltration, among the tested concentrations, NAD+ at 0.5-1.0 mM was most effective in decreasing halo blight disease. NAD+ at 2.5 mM applied as a foliar spray in rotation with Kocide 3000 (copper hydroxide) at 0.5 mg/ml further reduced the disease severity compared to Kocide 3000 alone. In the in-vitro study, no inhibitory effects of NAD+ were detected on the pathogen P. syringae pv. phaseolicola. Results of real-time polymerase chain reaction (qPCR) showed that the defense-related genes PR1, AZI1, EDS1, SARD1, PDF1.2, and PAL1 were up-regulated in the NAD+ treatment. Taken together, these data indicate that NAD+ significantly suppressed halo blight on snap bean, and application of NAD+ has the potential in management of this important disease.