Effects of Pseudomonas chlororaphis strain AFS009 and Beauveria bassiana strain GHA against Plumeria rust in Hawaii

This study examined the effects of beneficial rhizobacterium Pseudomonas chlororaphis strain AFS009 and entomopathogenic fungus Beauveria bassiana strain GHA against plumeria rust Coleosporium plumeriae. Two preemptive or three curative laboratory experiments and a curative field experiment were conducted to examine the effects of these commercially available biocontrol products. Treatments included the application of B. bassiana at 1.23 g/L and P. chlororaphis at 3 or 9 g/L. Systemic fungicide azoxystrobin applied at 0.12 g/L and water were included as positive and negative controls, respectively. While its effect was insignificant in the field trial, B. bassiana reduced the rust pustule development in one of two preemptive and two of three curative laboratory trials. In contrast, P. chlororaphis applied at 9 g/L suppressed the number of rust pustules in both laboratory and field experiments, demonstrating its potential biological activity against plumeria rust. In the field trial, the effect of P. chlororaphis was observed at 14 days post-treatment, suggesting that an application interval of 14 days on infected plants can take the rust under control.