LAUSR

The relative susceptibility of six Rutaceae family genotypes to bacterial citrus canker (CC) caused by Xanthomonas citri subsp. citri (Xcc) was assessed by measuring and comparing in planta bacterial populations over time following inoculation using a minimally destructive inoculation. These genotypes included lime (Citrus aurantifolia), grapefruit (C. paradisi), sweet orange (C. sinensis), calamondin (C. reticulata X C. japonica), kumquat (C. japonica), and orange jessamine (Murraya paniculata). Internal Xcc populations in orange jessamine plateaued early and remained significantly lower than other genotypes. Xcc populations increased rapidly in all other genotypes, decreasing precipitously and significantly over time in kumquat and calamondin as compared to the more susceptible genotypes sweet orange, grapefruit, and lime. Xcc populations in calamondin peaked by 7 DPI then began to fall significantly relative to the more susceptible genotypes sweet orange, grapefruit, and lime. Given the steep decline in populations in calamondin and kumquat, we compared water-soluble extracts from healthy leaf tissue from all previously investigated Citrus genotypes to determine if the extracts had any inhibitory effect on Xcc, implicating them in this abrupt population decline late in the infection process. Only extracts from calamondin leaf tissue significantly inhibited Xcc growth within 24 h. Potentially, constitutively produced inhibitory compounds in calamondin may result in less severe CC symptoms as a result of the rapid decline in Xcc populations.