Differential host range reaction of citrus and citrus relatives to citrus canker and citrus bacterial spot determined by leaf mesophyll susceptibility

The leaf mesophyll susceptibility of 54 citrus species, cultivars, and relatives to Xanthomonas campestris pv. citrumelo, the cause of citrus bacterial spot, was evaluated in Hastings, Florida, during 1989 and 1990. A similar host range of 53 citrus species, cultivars, and relatives was tested in Beltsville, Maryland, during 1991 to compare their differential susceptibility to X. c. citri, which causes citrus canker, and to X. c. citrumelo by inoculations on foliage of the same trees in replicated field plots. Field-grown trees were pruned to stimulate synchronous leaf flush for inoculation by a modified pinprick method. Lesion size at 60 days (Hastings plots) or 45 days (Beltsville plots) postinoculation was used to quantify leaf mesophyll susceptibility