Authors
K. L. Johnson, Department of Plant Pathology, University of Georgia, Athens 30602;
G. V. Minsavage, Department of Plant Pathology, University of Florida, Gainesville 32611;
T. Le, Department of Plant Pathology, University of Georgia;
J. B. Jones, Department of Plant Pathology, University of Florida; and
R. R. Walcott, Department of Plant Pathology, University of Georgia
Abstract
Bacterial fruit blotch (BFB), caused by the seedborne, gram-negative bacterium Acidovorax citrulli, is a serious threat to cucurbit seed and fruit production worldwide. Because of the lack of effective management strategies, we investigated the efficacy of a nonpathogenic A. citrulli strain as a biological control seed treatment for BFB. For this study, we generated a type III secretion system mutant of A. citrulli, AAC00-1ΔhrcC, that was nonpathogenic on watermelon but retained its ability to colonize germinating watermelon seed. With watermelon seed naturally infested with A. citrulli, AAC00-1ΔhrcC reduced BFB seedling transmission by 81.8% relative to control seed. In comparison, another A. citrulli antagonist, A. avenae strain AAA 99-2, reduced BFB seedling transmission by 74.6% for seed samples from the same lot. Additionally, when female watermelon blossoms were protected with AAC00-ΔhrcC and subsequently challenged with AAC00-1, the resulting seedlots displayed 8% BFB seedling transmission. This was not significantly different than seed from blossoms protected with AAA 99-2 (4%) but significantly less than those from blossoms protected with 0.1 M phosphate-buffered saline (36%). These results suggest that nonpathogenic A. citrulli has potential as a biological control seed treatment component in a comprehensive BFB management program.
