Burkholderia sp. SSG is a broad-spectrum antagonist against plant diseases caused by diverse pathogens

SSG, a Burkholderia isolate recovered from boxwood leaves, has many genes and gene clusters coding plant growth promoting traits and antagonistic activity against plant pathogens. It has been demonstrated that this bacterial isolate is a potent biofertilizer for boxwood and an effective biocontrol agent against boxwood blight. In this study we evaluated SSG against 21 additional pathogens including six bacteria, nine fungi and six Phytophthora species using dual culture assays, and against twelve diseases in planta under controlled environment. SSG suppressed all fungal and Phytophthora species, and five of the six Gram negative bacteria in dual culture. SSG provided the most consistent control to bacterial blight of geranium caused by Xanthomonas campestriscampestriscampestriscampestris at 41% to 58%, and to pansy leaf spot by Colletotrichum fnicticola at 30% to 32% across all three treatment timings from 1 day before inoculation (dbi) to 3 days after inoculation (dai). Among the six other diseases evaluated for multiple treatment timings, SSG provided the greatest control at 1 dbi to two diseases with hydrangea anthracnose by C. gloeosporioides at 67% and rhododendron Ramorum blight by Phytophhtora ramorum at 54%. The best SSG control of pansy gray mold by Botrytis cinerea was 67% at 1 wbi while that of tomato spotted wilt virus of impatiens was 53% at 2 wbi. When plants were treated with SSG only at one timing of 1 dbi, the best disease control was observed on Phytophthora blight of annual vinca by P. nicotianae at 95%, followed by pansy leaf spot by Alternaria tenuissima at 60%, Phytophthora blight of bell pepper by P. capsici at 56%, and Volutella blight of boxwood by Pseudonectria rouselliana at 44%. Further investigations into its efficacy for control of two root/crown rot diseases are warranted. Nevertheless, this study demonstrates that SSG is a promising broad-spectrum biocontrol agent for a variety of plant diseases caused by diverse pathogens.