Submitted to: Potato Association of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 22, 2005
Publication Date: July 1, 2005
Citation: Slininger, P.J., Schisler, D.A., Kleinkopf, G. 2005. Biological control of post harvest late blight of potatoes in storage by bacteria suppressive to fungal dry rot and sprouting. In: Potato Association of America Annual Meeting Proceedings, July 17-22, 2005, Calgary, Alberta, Canada. Paper No. G39. 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 liquid media and screened in wounded potato bioassays for their ability to suppress late blight incited by P. infestans (US-8, mating type A2). Stationary-phase bacteria were mixed with fungal zoospores to inoculate potato wounds with 5 mL containing ~10(8) bacterial CFU/mL and 2 x 10(4) zoospore count/mL. Disease suppressiveness was evaluated after tubers were stored one week at 15 degrees C and 90% relative humidity. Several of the BCA treatments reduced late blight by 25 to 60% (including three strains of Pseudomonas fluorescens and one of Enterobacter cloacae). Larger-scale pilot testing of these four strains, as individuals and in combination, was conducted by spraying 1.6 mL of 4 x 10(4) P. infestans sporangia/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 at 7.2 degrees C and 95% relative humidity for four weeks. All BCA treatments reduced disease. Disease suppression ranged from 35% (worst treatment)up to 86% (best) the first test year and from 35 to 91% the second year. Unwashed bacteria outperformed those washed free of culture broth.