Bacterial antagonists, zoospore inoculum retention time and potato cultivar influence pink rot disease development
2009
Schisler, David A. | Slininger, Patricia J. | Miller, Jeff S. | Woodell, Lynn K. | Clayson, Shane | Olsen, Nora
Zoospores or germinating encysted zoospores of the pathogen Phytophthora erythroseptica can cause new infections via tuber eyes, lenticels and cracks and cuts that result from tuber harvesting operations; infection courts that theoretically could be protected using microbial antagonists. Ten microbial antagonists that reduce Fusarium dry rot, late blight and/or sprouting in storage 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 48 h, diluted to a concentration of approximately 3 x 108 cfu/ml, individually combined with zoospores of P. erythroseptica, and the mixed microbial suspension was used to inoculate shallow puncture wounds on tubers. Data from full factorial experimental designs with ten levels of antagonist, two levels of cultivar, and two levels of inoculum age after inducing zoospore liberation from sporangia indicated that all factors influenced the size of pink rot lesions that developed internally around wound sites (P <= 0.05). In two different sets of experiments, Enterobacter cloacae strain S11:T:07 reduced lesion size more than the other antagonists (19% and 32% reduction versus the control) though Pseudomonas fluorescens bv. V S11:P:14, Pseudomonas sp. S22:T:04, and Enterobacter sp S11:P:08 also significantly reduced disease. 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. Significantly, zoospore inoculum 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 are discussed.
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