Improvement of biological control capacity of Paenibacillus polymyxa E681 by seed pelleting on sesame

Sesame is an important vegetable crop for the production of oil in Korea. The main obstacle of sesame cultivation is the occurrence of damping-off diseases and wilt caused by a complex of soil-borne pathogens in fields cultivated for two or more successive years. To protect sesame seedlings against these diseases, Paenibacillus polymyxa E681, a plant growth-promoting rhizobacterium (PGPR) previously shown to suppress disease incidence and promote growth on cucumber and pepper in the greenhouse and field experiments, was evaluated for its capacity for biological control and growth promotion in vitro and in situ. Seed treatment with strain E681 alone did not show consistent protection. Therefore, seed pelleting with strain E681 was attempted to increase the seed size and improve the stability and effectiveness of biocontrol capacity by strain E681. Through screening of pelleting materials, a combination of clay and vermiculite was selected for further experiments to enhance seed germination and root colonization of strain E681 on sesame. In greenhouse trials, formulations of strain E681 reduced disease incidence in disease-conducive soil. In the field, pelleting of sesame seeds with strain E681 significantly reduced pre- and post-emergence damping-off compared to the non-treated or pelleting alone controls; pelleting also promoted the plant growth and the grain yield. Furthermore, the efficacy of strain E681 for biological control and plant growth promotion was improved by sesame seed pelleting compared to the treatment with strain E681 alone. Hence, the application of strain E681 via seed pelleting offers potential to overcome some of the problems associated with successive years of sesame cultivation.