On citrus, the isolates showed significant
variation in their pathogenicity and
their ability to elicit host responses when
using infiltration inoculation (Figs. 1 and
2, Table 3). When a high concentration
(108
CFU/ml) of isolates 6177, 6758, and
1894 were infiltrated into newly expanded
citrus leaves, an HR-like symptom was
elicited (Fig. 1E). This HR-like symptom
was readily apparent at approximately 48 h
after inoculation, and abscission of inoculated
leaves occurred 24 to 48 h later. In
contrast, the HR elicited by X. citri pv.
citri strain AW and X. citri pv. aurantifolia
strain C on grapefruit appeared at least 72
h after inoculation, and the rapid abscission
of inoculated leaves was not observed
(data not shown). When the inoculum was
diluted 100-fold to 106
CFU/ml, these
isolates caused either chlorosis or no obvious
symptoms (Fig. 1E). Isolates 6268,
6269, and 6370, when infiltrated at high levels, caused raised lesions similar to
citrus canker disease after 1 to 2 weeks,
but only on grapefruit; on sweet orange
and key lime, only small, flat lesions with
raised margins appeared after 2 weeks.