Evaluation of Resistance to Leaf Scald by Quantitative PCR of Xanthomonas albilineans in Sugarcane

摘要

Leaf scald, caused by Xanthomonas albilineans, is a major sugarcane disease controlled primarily with host resistance. Because visual evaluation can be uncertain due to erratic symptom expression, a reliable resistance screening method is needed. A quantitative polymerase chain reaction (qPCR) with potential for resistance screening was used to compare bacterial populations in 31 clones at different times after inoculation, and the correlation with the visual symptom rating method was determined. Comparisons of bacterial populations quantified by qPCR and visual symptom severity ratings in systemically infected leaves showed variable results, with the highest correlation at 8 weeks after inoculation.To measure consistency, the correlation was determined among three ferent field experiments for data obtained with the same method at diffe times after inoculation. The qPCR assay was more consistent among periments compared with visual symptom rating at8 weeks after inoc tion. Susceptible check cultivars always had high bacterial populations the severe inoculation resulted in moderate to high bacterial population two of three resistant checks in some experiments. The results suggest qPCR can provide an improved method to evaluate resistance to leaf si in sugarcane; however, multiple experiments will be needed to accura determine clone resistance levels.