Survival of SSG, an Endophytic Burkholderia Biocontrol Agent, on the Boxwood Leaf Surface

Survival of Burkholderia cepacia complex (Bcc)-based biocontrol agents (BCA) has been associated with their field performance for foliage disease control. SSG, a strain of boxwood endophytic Bcc, suppresses a broad spectrum of plant foliage diseases, including boxwood blight, but the control efficacy declines over time. Factors affecting SSG survival on leaf surfaces were investigated to promote the application of the BCA for boxwood blight management. ‘Justin Brouwers' boxwood plants were treated with SSG cells at 107 to 108 colony-forming unit (CFU)·ml−1, maintained in a moist chamber at 10, 20, or 30 C (50, 68, 86 F), and sampled after the inoculum was blow-dried at 0, 3, 6, 12, and 24 h after treatment. The retained cells per leaf at 0 hours was 105 to 106 CFU, but only less than 10% of the cells survived 24 h after application, irrespective of the wet period and temperature. A wet condition of 12 and 24 h at 20 and 30 C facilitated SSG survival on the second day. Further survival of SSG was affected by temperature but not wetness. Damp conditions and pleasant temperatures can improve bacteria survival and stability and are keys to promoting BCA field applications. Index words: Biocontrol agent, endophyte, survival on plant surfaces, temperature, wetness. Species used in this study: Bacterium strain, SSG (Burkholderia sp);Plant species: Buxus sempervirens L. ‘Justin Brouwers'.