Detection and identification of bacterial contaminants from strawberry runner explants

Microbial contaminants were detected in surface-sterilized strawberry runner explants partially submerged in half-strength liquid Murashige and Skoog medium. From June to August, 1994, 45 of 70 strawberry genotypes were found to be contaminated, whereas from June to August, 1995, 53 of 72 contained contaminants. There were more bacterial than fungal contaminants. Bacterial contaminants from 22 strawberry genotypes were isolated, purified, and identified to genus by standard biochemical tests such as Gram's stain, motility, oxidase, and gelatinase, and carbon source utilization (Biolog Microplates, Biolog, Inc., Hayward, CA). Among the 30 isolates identified with the Biolog system, the majority were fluorescent pseudomonads including Pseudomonas fluorescens types A, F, and G. P. corrugate, P. tolaasii, P. paucimobilis, Xanthomonas campestris, Xanthomonas spp., and Enterobacter cloacae were also identified. Five Gram-negative and two Gram-positive contaminants could not be identified by the Biolog test. Biochemical tests were used to characterize the bacteria and to confirm Biolog test results. Bacteria identified in this study were soil, water, and plant related, indicating that efforts to reduce explant contaminant levels should be centered on the care of stock plants or the sterility of the watering system.