Reaction of genotypes of citrus species and varieties to Xanthomonas citri subsp. citri under greenhouse conditions.

Resistance of citrus genotypes to Asian citrus canker, caused by Xanthomonas citri subsp. citri (Xcc) was evaluated on 582 accessions (319 varieties of sweet orange), including varieties with a potential commercial use. All accessions were grown in a greenhouse and were spray-inoculated with Xcc to screen for resistance, based on analyses of lesion expansion. Inoculum (10(8) CFU/ml) was applied on the abaxial side of all leaves and all plants were incubated up to 30 days. Area of lesions on inoculated leaf blades was scanned and compared with healthy foliar area. A disease index was obtained and used to classify response to citrus canker. Two experiments were carried out with different varieties and distinct periods. A wide range of reaction was observed, with approximately 13% of all accessions resistant to citrus canker, 42% moderately resistant, 20% susceptible, and 25% highly susceptible.