Biocontrol of Fusarium sambucinum, dry rot of potato, by Serratia plymuthica 5-6

Serratia grimesii 4-9 and Serratia plymuthica 5-6, isolated from the rhizosphere of pea, Pisum sativum (L), were evaluated for their potential to suppress growth of Fusarium sambucinum in vitro and to reduce Fusarium dry rot in stored potatoes (Solanum tuberosum L). In vitro studies indicated that these bacterial isolates suppressed growth of F. sambucinum by 60% or more at both 15 and 25 degrees C. In a potato tuber slice assay the number of infection sites in potato slices exposed to F. sambucinum and treated with S. grimesii 4-9 and S. plymuthica 5-6 was reduced by 96 and 97%, respectively, at 15 degrees C. The diameter (mm) of the infection sites was reduced 91 and 96%, respectively, when compared to slices treated with F. sambucinum alone. Studies with Fusarium-infected whole potato tubers also showed significant reduction in dry rot formation following treatment with the bacterial isolates or the fungicide thiabendazole. When applied simultaneously with the pathogen, S. grimesii 4-9 and S. plymuthica 5-6 suppressed development of Fusarium dry rot by 60 and 77%, respectively, at 15 degrees C and by 63 and 84%, respectively, at 25 degrees C compared to tubers inoculated with the pathogen alone. Thiabendazole suppressed development of Fusarium dry rot by 66 and 81% at 15 and 25 degrees C, respectively, compared to tubers inoculated with the pathogen alone. These studies demonstrate the potential of soil bacteria as biofungicides for managing post-harvest crop diseases. Due to the potential risks to human health associated with S. grimesii 4-9, S. plymuthica 5-6 is recommended for further study for biofungicide development.