A quantitative method for inoculating strawberry leaves with Xanthomonas fragariae, factors affecting infection, and cultivar reactions

Abaxial surfaces of strawberry (Fragaria × ananassa) leaves were quantitatively inoculated with the causal agent of angular leaf spot, Xanthomonas fragariae, using a rigidly mounted spray gun device to examine factors affecting infection. Lesions were uniformly distributed within the inoculation sites, and their numbers increased as the distance between the spray nozzle and leaf surface decreased and the duration of the inoculation burst increased. Leaves of plants exposed to darkness before inoculation had low numbers of lesions, but numbers increased markedly after only 0.5 h of light and became maximal after 4 h, demonstrating the importance of inducing stomatal opening prior to inoculation. Exposing plants to a high or low preinoculation humidity did not affect lesion numbers, but incubating plants at a high postinoculation humidity resulted in greater numbers of lesions than those incubated at low humidity. Exposing plants to mist for 3 days following inoculation did not further increase lesion numbe...