Bacterial colonization of cuticular mutants of maize.
L. M. MARCELL and G. A. Beattie. Iowa State University, AMES, IA. Phytopathology 89:S48.

For many bacterial pathogens, large epiphytic populations contribute to a high probability of disease. To study the influence of the plant cuticle on leaf surface populations, we inoculated several glossy maize mutants, which are altered in their cuticles, with Pseudomonas syringae, a pathogen of corn, and Pantoea agglomerans, a corn saprophyte. For these studies, we selected 4 out of 11 mutants that had been previously characterized for their surface hydrophobicity, extractable cuticular waxes, and wax crystal morphology. Results showed that the tightly-associated populations, i.e. those not released by sonication, increased dramatically from 2% to 85% over 5 days, indicating that bacteria either became firmly attached to the leaf surface, or that colonization of internal spaces increased over time. The mutants all retained greater initial numbers of bacteria than did the wild type. For the pathogen, the leaf-associated populations decreased faster on the mutants than on the wild type following inoculation, suggesting that increased leaf surface hydrophilicity did not improve colonization as expected. For the saprophyte, the population dynamics on 3 of the mutants were not significantly different than on the wild type. Interestingly, the saprophyte exhibited a significantly different pattern of colonization on gl4, which is the mutant that was most similar to the wild type in surface hydrophobicity, wax quantity and wax crystal morphology. The increased size of the populations of the saprophyte on gl4 suggests that the cuticle of gl4 offers a more favorable habitat for bacterial colonization than the wild type or the other 3 mutants that were tested.