Evaluation of Endophytic Bacteria as Potential Biological-Control Agents for Oak Wilt

Abstract

Endophytic bacteria were isolated from surviving live oaks (Quercus fusiformis) in Texas, where oak wilt is epidemic, and evaluated as potential biological control agents for the disease. Of the 889 bacterial isolates tested, 183 showed in vitro inhibition of the pathogen, Ceratocystis fagacearum. Six isolates were further evaluated for colonization of containerized Spanish oaks (Quercus texana) and live oaks. In general, when injected into the stems, Bacillus species colonized Spanish oaks more extensively than Pseudomonas species; whereas, the opposite was true for live oaks. In containerized live oaks inoculated with the oak wilt pathogen, preinoculation with Pseudomonas denitrificans 1-15 reduced the number of diseased trees by 50% and in the same trial decreased the percentage of crown loss by 17%. In a second trial, no reduction in numbers of diseased trees was observed; however, preinoculation with either strain 1-15 or Pseudomonas putida 5-48 significantly reduced crown loss. These studies indicate that a potential exists for the utilization of selected bacteria to control oak wilt.