Management of Root Rot Disease in Snap Beans Using Biological Control Agents

Jacqueline Joshua, Tennessee State University


Snap bean (Phaseolus vulgaris) is an annual, warm-season group of common beans selected for their succulent pods. Recently there has been an increasing demand for fresh vegetables in the US. However, the production of snap beans is constrained by the prevalence of diseases mainly root rots. Root rots are commonly managed through frequent fungicide applications, which could have some detrimental impact to the environment and people as well as reducing the grower’s profit by increasing production cost. Charcoal rot is a major root rot disease in snap beans and currently, there are no commercially available fungicide labeled to effectively control it; thus, requiring alternative disease management strategies like the use of biological control agents (BCA). The objectives of this study were to isolate, identify and evaluate selected BCAs for their bioactivity against diverse fungal pathogens in vitro by using dual culture technique and in vivo via seed treatments. Bacillus vallismortis (‘PS’), B. amyloliquefaciens (‘Psl’), B. subtilis (‘Prt’), Enterobacter sp. (‘E’) and B. thuringiensis (‘Y’) were isolated from papaya stem, root, snap bean root and dogwood stem respectively. Results showed the presence of significant variation in the growth inhibition by these BCAs against diverse pathogens in vitro. Of the BCAs evaluated, Macrophomina phaseolina was the most inhibited pathogen. Biological control agents evaluated included (‘Prt’, ‘PS’, ‘Psl’, ‘IMC8’ and ‘Y’) which were all Bacillus species showing over 50 % inhibition. Bacillus and Enterobacter isolates can be used as BCA for controlling charcoal rot disease. Bacillus vallismortis showed significantly higher chlorophyll content compared to the control and isolate ‘B17B’ (Serratia) was observed to colonize snap bean roots following a seed treatment with gfp-tagged ‘B17B’ isolate. This study also resulted in the identification of several volatile compounds with antimicrobial activity (cycloheptasiloxane tetradecamethyl-, cyclotetrasiloxane and octamethyl, 2, 3-dimethyldecane). The understanding of mechanisms by which these BCAs provide disease reduction are valuable for providing a path toward the full integration into the current disease management systems for root rot. It also paves a path for a large-scale evaluation that will lead to their adaptability by the industry sector for potential development of bio rational products.

Subject Area

Biology|Plant Pathology

Recommended Citation

Jacqueline Joshua, "Management of Root Rot Disease in Snap Beans Using Biological Control Agents" (2017). ETD Collection for Tennessee State University. Paper AAI10267510.