FACTORS AFFECTING THE SURVIVAL AND SPREAD OF ACIDOVORAX-AVENAE SUBSP CITRULLI IN WATERMELON TRANSPLANT PRODUCTION FACILITIES

Survival of the watermelon fruit blotch pathogen (Acidovorax avenae subsp. citrulli) on plastic transplant production trays and dissemination of the pathogen in the greenhouse was studied. Bacteria survived 63 days on nontreated trays containing residues of potting substrate and root debris. Longevity of the pathogen decreased with increasing storage temperature. Fruit blotch bacteria were not detected on contaminated plastic trays after the trays were immersed for 5 min in a sodium hypochlorite (10% household bleach) solution. Standard greenhouse sanitation practices should preclude perennation of the pathogen associated with plastic trays used for watermelon seedling production. Overhead irrigation of seedlings resulted in greater levels of pathogen spread. Reduced relative humidities after overhead irrigation resulted in diminished levels of disease. The lowest incidence of disease occurred when trays were subirrigated. Copper hydroxide applied prior to irrigation also reduced disease levels. The threat of serious watermelon fruit blotch epidemics in transplant production facilities can be significantly reduced by eliminating the mechanism for splash dispersal, reducing atmospheric moisture, and using copper sprays as protectants.