Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 1996
Publication Date: N/A
Interpretive Summary: Fusarium dry rot causes an estimated 100-400 million dollars of losses in potato storage houses each year and, for tubers stored for human consumption, is no longer controllable with fungicides. We previously found 18 strains of bacteria that are capable of controlling dry rot in laboratory and field tests. In order to increase the likelihood that this discovery will be developed into a commercial product helpful to USDA-ARS customers, the present work was conducted to determine how many cells of bacteria are needed to control Fusarium dry rot, how the level of control changes when less bacterial cells are used, and how we could get more disease control to take place from small doses of bacterial cells. We determined that decreasing the number of bacterial cells proportionally decreased disease control. However, when the cells of two different bacteria were combined using 1/100 the usual number of cells, we discovered that some combinations of bacteria gave control as good as obtained with a full dose of one bacterium. This discovery makes the development of a biological control product active against dry rot of potatoes even more likely since it could be much less expensive to produce an effective product that only requires 1/100 the usual amount of active ingredient. The commercialization and use of a biological control product active against Fusarium dry rot would decrease the amount of pesticide residues on potatoes and in the environment.
Technical Abstract: Eighteen bacterial strains were individually assayed against Gibberrella pulicaris (5 x 10**5 conidia/ml) by coinoculating antagonist and pathogen into wounds in Russet Burbank potatoes. All antagonist concentrations (10**6,10**7, and 10**8 cfu/ml) decreased disease (38-76% vs control, P<0.05). When 4 strains were assayed at 11 concentrations (range: 10**5-10**8 cfu/ml) against G. pulicaris, linear regression of the log-dose, log-response data was significant for all 4 strains (P=0.001-0.01, R**2=0.50-0.74). Challenging G. pulicaris with all possible antagonist pairings within two sets of 10 antagonist strains (5 x 10**5 cfu/ml of each strain) resulted in 16 of 90 pairs controlling disease better than predicted from averaging the performance of individual strains making up the pair (P<0.10). Successful pairs reduced disease by 70% vs controls, a level of control comparable to control obtained with 100x the inoculum dose of a single antagonist strain. Strain genus or soil of origin were not useful in predicting successful pairings. Scanning electron microscopy revealed a highly variable topography within puncture wounds in potatoes, representing a diverse colonization environment for bacterial antagonists and conidia of G. pulicaris. The economic feasibility of producing a mixed microbial biological control product and the effect of liquid culture production of cell biomass on dose-response curves and mixed microbial product performance are discussed.