RESUMO
Verticillium dahliae is a fungal pathogen that causes wilt disease in a wide range of host plants. Characterization of virulence, morphological, and molecular variations among V. dahliae isolates from different geographic origins is essential for any breeding program aimed at producing plant cultivars resistant to this disease. We characterized virulence variation among V. dahliae isolates from Chinese cultivated eggplant grown in Northeast China by pathogenicity testing on susceptible, moderately resistant, and resistant eggplant accessions in a glasshouse using a root-dipping method of infection. These isolates were also characterized for morphological features based on growth on potato dextrose agar media and for genetic variation based on ISSR markers. All 12 isolates were divided into three pathotypes based on the virulence, i.e., strong, moderate, or weak type. Three isolates were categorized as defoliating pathotypes, with strong virulence, and the rest of the isolates were categorized as non-defoliating pathotypes, with moderate to weak virulence. The eggplant isolates were classified into three morphological types or morphotypes, hypha, hypha-sclerotia, and sclerotia; no significant correlations were detected between pathotypes and morphotypes or geographic origins. ISSR fingerprinting indicated genetic diversity among isolates, ranging from 0.26 to 0.69. Specific fingerprint types were not correlated with either pathotype or morphotype. However, ISSR analyses did reveal two clusters in which the isolates in each share the same or neighboring geographic origins.
Assuntos
Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Solanum melongena/microbiologia , Verticillium/genética , China , Impressões Digitais de DNA/métodos , Variação Genética , Geografia , Raízes de Plantas/microbiologia , Virulência/genéticaRESUMO
Symptoms resembling giant calyx, a graft-transmissible disease, were observed on 1-5 % of eggplant (aubergine; Solanum melongena L.) plants in production fields in Sao Paulo state, Brazil. Phytoplasmas were detected in 12 of 12 samples from symptomatic plants that were analysed by a nested PCR assay employing 16S rRNA gene primers R16mF2/R16mR1 followed by R16F2n/R16R2. RFLP analysis of the resulting rRNA gene products (1.2 kb) indicated that all plants contained similar phytoplasmas, each closely resembling strains previously classified as members of RFLP group 16SrIII (X-disease group). Virtual RFLP and phylogenetic analyses of sequences derived from PCR products identified phytoplasmas infecting eggplant crops grown in Piracicaba as a lineage of the subgroup 16SrIII-J, whereas phytoplasmas detected in plants grown in Bragança Paulista were tentatively classified as members of a novel subgroup 16SrIII-U. These findings confirm eggplant as a new host of group 16SrIII-J phytoplasmas and extend the known diversity of strains belonging to this group in Brazil.