Screening citrus genotypes for resistance to canker disease (Xanthomonas axonopodis pv. citri)

With 3 figures and 3 tables Citrus canker (Xanthomonas axonopodis pv. citri) has brought great damage to citrus industry worldwide, and it is difficult to control, so the use of resistant genotypes seems the only choice. All the tested citrus species showed typical symptoms when artificial inoculation was performed. The present study aimed to find genotypes possessing active resistance to canker disease. A total of 14 accessions from three species were investigated by puncture inoculation of excised leaves with the pathogen, and it was found that 'Huaihua', 'Sanye' and 'No.25-86' in Citrus ichangenesis, 'Shenju' and 'Zhencheng' in C. junos had fewer disease spots on pin-holes with delayed symptom appearance; while 'Chinese Citron' (C. medica) did not show any lesions. These six genotypes were further tested in an epidemic field by inoculation with 2.5 x 10⁷ cfu/ml of pathogen solution for 2 years. Only the tested citron showed complete and active resistance, with tissue necrosis on the pin-holes; the other five accessions were all infected with different disease incidences. Therefore, the citron accession was considered as a resistant genotype, and was already used for resistant cultivar breeding.