title: Modulation of oxidative responses by a virulent isolate of Colletotrichum fructicola in apple leaves.
abstract: Apple bitter rot (ABR) and Glomerella leaf spot (GLS) can be caused by Colletotrichum fructicola. Although both diseases can occur simultaneously in orchards, some isolates show clear organ specialization. Thus, this work was aimed to compare microscopically the development of preinfective structures of ABR- and GLS isolates and their impact on the enzymatic oxidant defense system during the leaf infection process. On leaves, conidial germlings of GLS-isolate formed appressoria mostly sessile. In contrast, those of ABR-isolate were pedicellate and formed multiple melanized appressoria probably as a sign of unsuccessful infection attempts. Neither ABR- nor GLS isolate triggered hypersensitive response in apple leaves. In overall, the activity of scavenging enzymes was higher and long-lasting in leaves inoculated by GLS- than by ABR isolate and control. Guaiacol peroxidase, catalase, and glutathione reductase had activity peaks within 24 h after inoculation (HAI). Ascorbate peroxidase activity was higher only in GLS-infected leaves at 6 HAI, while superoxide dismutase remained unaltered. A lower level of hydrogen peroxide (H2O2) was determined in GLS-infected plants at 48 HAI, but the electrolyte leakage markedly increased. Disease symptoms in leaves were only caused by GLS-isolate. Results suggest that the virulent isolate coordinately downregulates the oxidative plant defense responses enabling its successful establishment in apple leaves.
authors.affiliation: Laboratory of Plant Pathology, Agricultural Science Center, Federal University of Santa Catarina, Rod. Admar Gonzaga 1346, 88034-001 Florianópolis, Santa Catarina, Brazil.
authors.forename: Aline Cristina
authors.initials: AC
authors.lastname: Velho
authors.affiliation: Laboratory of Plant Pathology, Agricultural Science Center, Federal University of Santa Catarina, Rod. Admar Gonzaga 1346, 88034-001 Florianópolis, Santa Catarina, Brazil.
authors.forename: Mathias F
authors.initials: MF
authors.lastname: Rockenbach
authors.affiliation: Department of Plant Protection, Faculty of Agronomy, University of the Republic, Av. Garzón 780, CP 12900 Montevideo, Uruguay.
authors.forename: Pedro
authors.initials: P
authors.lastname: Mondino
authors.affiliation: Laboratory of Plant Pathology, Agricultural Science Center, Federal University of Santa Catarina, Rod. Admar Gonzaga 1346, 88034-001 Florianópolis, Santa Catarina, Brazil. Electronic address: marciel.stadnik@ufsc.br.
authors.forename: Marciel J
authors.initials: MJ
authors.lastname: Stadnik
mesh_terms: D020231:Colletotrichum / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000378:metabolism; D006861:Hydrogen Peroxide; D027845:Malus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D018384:Oxidative Stress; D009195:Peroxidase / Q000235:genetics / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D013172:Spores, Fungal / Q000145:classification / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D006861:Hydrogen Peroxide; C121048:guaiacol peroxidase; D009195:Peroxidase; D013482:Superoxide Dismutase
keywords: Apple bitter rot; Glomerella leaf spot; Hypersensitive response; Oxidative stress enzymes; Reactive oxygen species