The effect of the leaf surface waxes of maize on bacterial colonization.
Lise M. Marcell and Gwyn A. Beattie, Iowa State University, Ames, IA

The influence of specific plant traits on bacterial colonization of leaves is poorly understood. We evaluated the influence of leaf surface waxes on bacterial leaf colonization using four maize (Zea mays L.) mutants that were altered in loci affecting the biosynthesis of the cuticular waxes. These mutants varied greatly in their leaf surface topography, leaf wettability and the quantity and quality of their cuticular waxes, and were 93-99% genetically identical to the wild type. We found that Clavibacter michiganensis subsp. nebraskensis (Cmn) established significantly larger populations on two of the mutants, gl1 and gl4, than on the wild type, but established similarly sized populations on the mutants gl3 and gl5gl20 and the wild type. These increases resulted from a combination of enhanced survival in the first 24 h after inoculation, an increased rate of growth after 24 h, and an increase in the carrying capacity of the mutants for Cmn. In contrast, Pantoea agglomerans established significantly larger populations on only one mutant, gl4, and this increase resulted primarily from enhanced survival following inoculation. The leaf surface properties of gl4 suggest that it may promote bacterial survival by prolonging the residence time of water during periods of drying. Interestingly, mutant gl5gl20 negatively impacted the development of P. agglomerans populations. These results provide evidence that leaf surface waxes influence bacterial colonization of leaves, and imply that changes in these characteristics, such as result from air pollutants and global climate change, could influence the size of leaf-associated bacterial populations.