Natural variability in Arabidopsis thaliana germplasm response to Xanthomonas campestris pv. campestris

this work aimed to study the interaction between the model plant arabidopsis thaliana and xanthomonas campestris pv. campestris (xcc), the pathogen responsible for black rot of crucifers. the response of 32 accessions of a. thaliana to the brazilian isolate of xcc cnph 17 was evaluated. no immunity-like response was observed. "cs1308", "cs1566" and "cs1643" grown in continuous light were among the accessions that showed strongest resistance when inoculated with 5 x 106 cfu/ml. in contrast, "cs1194" and "cs1492" were among the most susceptible accessions. similar results were obtained when plants were grown under short-day conditions. to quantify the differences in disease symptoms, total chlorophyll was extracted from contrasting accessions at different time points after inoculation. chlorophyll levels from controls and xcc inoculated plants showed a similar reduction in resistant accessions, whereas xcc-inoculated susceptible accessions showed a greater reduction compared to controls. to test the specificity of resistance, accessions cs1308, cs1566, cs1643 and cs1438 (which showed partial resistance to cnph 17), were inoculated with a more aggressive isolate of xcc (cnph 77) and ralstonia solanacearum. among the accessions tested, "cs1566" was the most resistant to xcc cnph 77 and also displayed resistance to r. solanacearum. accessions cs1308, cs1566 and cs1643 were also inoculated with a high titer of xcc cnph 17 (5 x 108 cfu/ml). no collapse of tissue was observed up to 48 h after inoculation, indicating that a hypersensitive response is not involved in the resistance displayed by these accessions.