In field resistance to asiatic citrus canker of Citrus spp. genotypes.
W. M. Nunes (1), S. A. Carvalho (2), J. Belasque (3), A. M. O. Gonçalves-Zuliani (1), M. A. Machado (4), J. Croce Filho (5), Z. Abdo (6), C. H. BOCK (7). (1) Universidade Estadual de Maringa, Maringa, Parana, Brazil; (2) Instituto Agronomico de Campinas, Cordeiropolis, Brazil; (3) Universidade de Sao Paulo, Piracicaba, SP, Brazil; (4) Instituto Agronomico de Campinas, Cordeiropolis, SP, Brazil; (5) Agencia
Asiatic citrus canker (ACC), caused by <i>Xanthomonas citri </i>ssp.<i> citri</i> causes 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 <i>Citrus</i> representing 9 species (<i>C. aurantifolia</i>, <i>C. aurantium</i>, <i>C. clementina</i>,<i> C. deliciosa</i>, <i>C. limon</i>, <i>C. paradisi</i>, <i>C. reticulata</i>, <i>C. sinensis, </i>and <i>C. unshui</i>, and) and 4 hybrids (<i>C. reticulata</i> x <i>C.</i> sp, <i>C. reticulata</i> x <i>C. paradisi</i>, <i>C. reticulata</i> x <i>C. sinensis</i>, and <i>C.</i> <i>unshui</i> x <i>C. sinensis</i>). The number of lesions per leaf was assessed eighteen times from 2005 to 2010 (≤4 times per year). Mixed model analysis of fixed and random effects showed six resistance-susceptibility groupings of species and hybrids. The most resistant species grouping included <i>C. unshui</i> and <i>C. limon </i>(mean lesions per leaf of 4.32 and 4.26, respectively), and the most susceptible species were <i>C. paradisi</i> and <i>C. aurantifolia</i>, with 14.84 and 10.96 lesions per leaf, respectively. Other species (<i>C. reticulata</i>, <i>C. aurantium</i>, C<i>. deliciosa</i>, and <i>C. sinensis</i>) had intermediate severity (5.48 to 9.56 lesions per leaf). Hybrids had a range of ACC severity, and were in the more resistant groupings (5.26 to 7.35 lesions per leaf). 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 locations where ACC is an issue.
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