Interaction effect between inoculations of Pantoea agglomerans and pathogenic fungus Fusarium oxysporum on the growth of sweet potato in a pot experiment

We conducted a dual culture test between bacterium Pantoea agglomerans strain MY1 and pathogenic fungus Fusarium oxysporum strain BM3 to examine antagonistic activity of the bacterium. We observed the suppression of mycelial growth around the MY1-colony, which was a wetting-out action on Fusarium mycelia. In a co-inoculation pot experiment of P. agglomerans and F. oxysporum, the roots of sweet potato young plants were immersed in 30 mL of MY1 culture for 24 h to inoculate P. agglomerans before transplantation to pots, and autoclaved MY1 culture treatment was performed as an offset control of nutrients. While inoculating F. oxysporum, two 1 cm2 pieces of BM3 plate culture were attached to the side surface of the root just before transplantation. After 46 d of cultivation, the total dry weight (shoot + root) was measured and analyzed using ANOVA. The results were as follows: 1) the inoculation with BM3 significantly decreased dry weight; 2) in the effect of MY-inoculation with three levels of with and without inoculation of MY1 and addition of autoclaved MY1, there was a significant difference, but plant growth-promoting effect of the inoculation with MY1 compared to the offset control could not be detected; and 3) the interaction effect between BM3-inoculation and MY1-inoculation was significant. This interaction effect suggests that inoculation with MY1 culture suppressed the growth inhibitory effect of BM3-inoculation. These results suggest that the bacterium P. agglomerans strain MY1 has a suppressive effect on the growth inhibition caused by Fusarium stem rot fungus in sweet potatoes.