Bacterial Antagonists, Zoospore Inoculum Retention Time, and Potato Cultivar Influence Pink Rot Disease Development

Authors: Schisler, David; Slininger, Patricia - Pat; MILLER, JEFF - UNIVERSITY OF IDAHO; WOODELL, LYNN - UNIVERSITY OF IDAHO; CLAYSON, SHANE - UNIVERSITY OF IDAHO; OLSEN, NORA - UNIVERSITY OF IDAHO

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2009
Publication Date: 1/28/2009
Citation: Schisler, D.A., Slininger, P.J., Miller, J.S., Woodell, L.K., Clayson, S., Olsen, N. 2009. Bacterial antagonists, zoospore inoculum retention time, and potato cultivar influence pink rot disease development. American Journal of Potato Research. 86:102:111. DOI: 10.1007/s12230-008-9066-7

Interpretive Summary: Pink rot of potato causes severe disease on potato plants and in stored tubers in many potato growing regions of the world including North America. The disease is especially difficult to control in potato storages since the organism that causes the disease has become increasingly resistant to chemical control methods and potato resistance to the disease is not very high. In our laboratory, we previously discovered biocontrol agents that reduce one or more potato tuber storage maladies including dry rot, late blight and sprouting. In this study, we found that 4 of our biocontrol agents also reduced pink rot on two different cultivars of potatoes. The level of reduction in pink rot ranged from 19 to 32% for the best biocontrol agent. We also found that the biocontrol agents reduced the disease regardless of the form that the pathogen’s infectious units were in. These results demonstrate the utility that these biocontrol agents can have in reducing pink rot and the potential benefit of these strains to producers of potatoes and potato storage operators that are suffering economic losses due to this disease.

Technical Abstract: Pink rot of potato, primarily incited by Phytophthora erythroseptica, is a disease of importance in many potato growing regions of the world including North America. The principal mode of entry by the pathogen into tubers in storage is via wounds or eyes; surfaces that theoretically could be protected using microbial antagonists. Ten microbial antagonists known to reduce one or more of the potato tuber storage maladies dry rot, late blight and sprouting were assayed for efficacy against pink rot on tubers of cultivars Russet Burbank and Russet Norkotah. Antagonist strains were grown in a semidefined liquid medium at 25 C for 48h, diluted to a concentration of approximately 3 x 10E+8 cfu/ml, individually combined with zoospores of P. erythroseptica, and the mixed microbial suspension used to inoculate shallow puncture wounds on tubers. Data from full factorial experimental designs with 10 levels of antagonist, 2 levels of cultivar, and 2 levels of inoculum age after inducing zoospore liberation from sporangia indicated that all factors influenced the size of pink rot lesions on tubers (FPLSD, P less than 0.05). Enterobacter cloacae S11:T:07, P. fluorescens bv. V S11:P:14, Pseudomonas sp. S22:T:04, and Enterobacter sp S11:P:08 reduced lesion size with strain S11:T:07 reducing lesion size by 19% and 32% in two different sets of experiments. Lesion size was greater on Russet Norkotah than Russet Burbank tubers (42.3 and 26.5 mm, respectively), but cultivar did not influence antagonist performance as determined by comparing relative performance indices of individual antagonist efficacy on each cultivar. Zoospore innoculum of the pathogen incited smaller lesions in the early stages of individual bioassays than occurred later in bioassays when most zoospores had encysted. The implications of inoculum potential changing over the course of conducting bioassay experiments on pink rot is discussed.