Sérgio Alves de Carvalho, Centro de Citricultura “Sylvio Moreira”, Instituto Agronômico de Campinas (IAC), 13490-970, Cordeirópolis, SP, Brazil;
William Mário de Carvalho Nunes, Núcleo de Pesquisa em Biotecnologia Aplicada, Universidade Estadual de Maringá, 87020-900, Maringá, Paraná, Brazil;
José Belasque, Jr., Departamento de Fitopatologia e Nematologia, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Piracicaba, SP, Brazil;
Marcos Antonio Machado, Centro de Citricultura “Sylvio Moreira”, IAC;
José Croce-Filho, Secretaria de Estado da Agricultura e do Abastecimento do Paraná, Maringá, PR, Brazil;
Clive H. Bock, United States Department of Agriculture–Agricultural Research Service (USDA-ARS)-SEFTNRL, Byron, GA 31008; and
Zaid Abdo, USDA-ARS-SAA, Athens, GA 30605
Asiatic citrus canker (ACC) is caused by Xanthomonas citri subsp. citri. The disease results in yield loss and renders fruit unfit for the fresh market. A 6-year study in Paraná State, Brazil, was conducted to compare the susceptibility of 186 genotypes of citrus representing sweet orange (Citrus sinensis), mandarin (C. reticulata), Mediterranean mandarin (C. deliciosa), Clementine mandarin (C. clementina), Satsuma mandarin (C. unshiu), sour orange (C. aurantium), lemon (C. limon), sweet lime (C. aurantifolia), grapefruit (C. paradisi), and four hybrids (C. reticulata × Citrus sp., C. reticulata × C. paradisi, C. reticulata × C. sinensis, and C. unshiu × C. sinensis). Sweet orange (C. sinensis) was represented by the most genotypes (n = 141). The number of lesions per leaf was assessed 18 times from 2005 to 2010 (up to 4 times per year). The data were analyzed using mixed-model analysis of fixed and random effects, which showed a total of six resistance-susceptibility groupings of species and hybrids. Based on species, the most resistant genotypes, on average, included Satsuma and lemon (mean lesions per leaf = 4.32 and 4.26, respectively), and the most susceptible genotypes were grapefruit and sweet lime, with 14.84 and 10.96 lesions per leaf, respectively. Genotypes of mandarin, sour orange, Mediterranean mandarin, and sweet orange had intermediate severity (5.48 to 9.56 lesions per leaf). The hybrids also showed a range of ACC severity but all were in the more resistant groupings (5.26 to 7.35 lesions per leaf). No genotype was immune to ACC. The most resistant genotype was ‘Muscia’ (C. reticulata) and the most susceptible was ‘Valencia Frost’ (C. sinensis) (1.86 and 14.78 lesions per leaf, respectively). Approximately one-sixth of the genotypes showed a negative relationship of mean lesions per leaf with time, suggesting increasing resistance as they aged, due to a reduction in either new flush or plant size and structure. These results of the relative susceptibility of different citrus genotypes can be used in future research and to assist in varietal selection or for breeding purposes both within Brazil and other regions where ACC is an issue.