|Slininger, Patricia - Pat|
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2007
Publication Date: 6/11/2007
Citation: Slininger, P.J., Schisler, D.A., Ericsson, L.D., Brandt, T., Frazier, M.J., Woodell, L., Olson, N., Kleinkopf, G. 2007. Biological control of post-harvest late blight of potatoes. Biocontrol Science and Technology. 17(5/6):647-663.
Interpretive Summary: Phytophthora infestans is considered to be the most significant pathogen of potatoes worldwide and historically was the cause of widespread late blight that resulted in the Great Potato Famine of the 1840's. The introduction of US-8 genotypes of this pathogen has coincided with an increase in severity of late blight in North America. Members of the Potato Association of America have placed the development of sustainable agricultural practices, involving more effective and efficient use of fungicides in combination with resistant cultivars, as a high priority need to keep late blight disease in check. We tested late blight suppression by our eighteen patented beneficial soil bacteria which inhibit the development of both dry rot disease and sprouting of stored potatoes. In repeated laboratory experiments at NCAUR and small pilot studies simulating commercial conditions at the University of Idaho Kimberly Research and Extension Center, we found that several of the bacteria consistently suppressed late blight of stored potatoes. Disease reduction ranged from 25 to 91 percent. These findings impact the potato industry by showing the potential of these patented bacteria as an efficient, environmentally compatible means to biologically control late blight, dry rot, and sprouting with only one treatment applied to tubers entering storage.
Technical Abstract: Introduction of US-8 genotypes of Phytophthora infestans has coincided with an increase in severity of potato late blight in North America. As alternatives to chemical fungicides, 18 bacterial strains patented as biological control agents (BCA) of both sprouting and Fusarium dry rot were cultivated in three liquid media and screened in wounded potato bioassays for their ability to suppress late blight incited by P. infestans (US-8, mating type A2). Washed or unwashed stationary-phase bacteria were mixed with fungal zoospores to inoculate potato wounds with 5 µL containing ~10**8 bacterial CFU/mL and 2 x 10**4 zoospore count/mL. Disease suppressiveness was evaluated after tubers were stored a week at 15 degrees C, 90 percent relative humidity. One-fifth of the 108 BCA treatments screened, reduced late blight by 25 to 60 percent, including among other strains Pseudomonas fluorescens S22:T:04 (showing most consistency), P22:Y:05, S11:P:12 and Enterobacter cloacae S11:T:07. Small-scale pilot testing of these four strains, alone and in combination, was conducted under conditions simulating a commercial application. Suspensions of 4 x 10**4 P. infestans sporangia/mL were sprayed at a rate of 1.6 mL followed by 0.8 mL of bacteria treatment at ~5 x 10**9 CFU/mL per each of 90 unwounded potatoes. Three replicate boxes per treatment (30 tubers per box) were randomized in storage and maintained 4 weeks at 7.2 degrees C, 95 percent relative humidity. All BCA treatments significantly reduced disease; and unwashed bacteria outperformed those washed free of culture broth. Disease suppression ranged from 35 percent (worst treatment) up to 86 percent (best) the first test year and from 35 to 91 percent the second year. Highest overall performance rankings significantly above the control were achieved by the following strains in culture broth: four-strain mix > P. fluorescens S22:T:04 > P. fluorescens S11:P:12. Combined with previous demonstrations of dry rot and sprout suppression, the consistent late blight control by these strains and strain mixtures suggests the commercial feasibility of a single treatment for broad spectrum suppression of post-harvest potato diseases and sprouting.