Resistance evaluation of sweet orange (Citrus sinensis) cultivars to Xanthomonas citri subsp. citri

Abstract Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri, is responsible for significant economic losses of citrus in Brazil and elsewhere. The disease occurs in all regions of commercial production of sweet orange (C. sinensis L. Osbeck). Compared to chemical control, deploying canker-resistant cultivars is a viable and economical alternative for management of the disease. The objectives of this study were to compare the resistance to citrus canker of 14 genotypes of sweet orange, and to verify the levels of various enzymes involved in the canker resistance response, specifically peroxidase, catalase, and superoxide dismutase. The 14 genotypes included were Hamlin, Vermelha, Pera EEL, Pera IAC, Pera Bianchi/CC, Pera Ipiguá, Pera IAC 2000/1, Pera Ovale Siracusa, Pera Ovale, Pera IAC 2000/2, Pera M5, Pera Arapongas, Pera 58 and Pera 59. The varieties were evaluated under greenhouse conditions, through inoculation of leaves with X. citri subsp. citri, strain Xcc 306. After inoculation, measurements of lesion diameter and biochemical analyses were performed. Significant differences in resistance to X. citri subsp. citri between the citrus genotypes were observed, with cultivars Pera IAC and Pera EEL having significantly or numerically the smallest diameter canker lesions. Cultivar Pera IAC showed elevated levels of peroxidase, catalase and superoxide dismutase, enzymes known to be involved in resistance response to pathogen invasion. Cultivars with a strong resistance response to infection, and that produce smaller lesions are likely good candidates for commercial production or for use in breeding programs.