Caracterização morfológica, fisiológica, isoenzimática e controle de isolados de Corynespora cassiicola (Berky & Curt) Wei, agente causal da mancha alvo
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2008-06-27
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Universidade Federal de Goiás
Resumo
Corynespora cassiicola is the causal agent of target spot of several crops of
economical importance such as soybean, cotton, tomato, cucumber etc. Sixteen isolates of
this fungus from several hosts and different regions in Brazil were obtained and conducted
morphologic, physiologic, isozymic characterization as well as control, in laboratory and
in greenhouse of the Center of Research in Phytopathology of Escola de Agronomia e
Engenharia de Alimentos, da Universidade Federal de Goiás , located in Goiânia, State of
Goiás. The main objectives of this investigation were to characterize: a) morphology: by
determination of dimensions and number of pseudosepta in one hundred spores of each
isolate; b) physiology: by evaluating mycelial growth under different temperatures (15oC,
20oC, 25oC, 30oC and 35oC) and photoperiods (0, 12 and 24 hours); sporulation in
different photoperiods; hours of continuous humidity to improve spores germination; the
pathogenicity of several isolates of C. cassiicola by inoculation on several hosts
(cucumber, soybean, cotton, coffee, Barbados cherry, tomato and melon) and the
preservation of 10 isolates using three methods: Castellani, mineral oil and periodic
transfer; c) isozyme analysis: with polyacrylamide gel eletrophoresis of esterase of 14
isolates; and d) control: by reactions of nine cucumber hybrids to C. cassiicola; and the
sensibility of six isolates of C. cassiicola to eight fungicides in vitro (captan, chlorotalonil,
mancozeb, azoxystrobin, difeconazole, carbendazim, tebuconazole and thiophanatemethyl)
using concentrations of 0, 1, 10, 100 e 1000 μg mL-1; fungicide treatment of
cucumber plants inoculated with C. cassiicola. The following results were obtained: a) the
dimensions (length and width) of spores were in accord with the key for the identification
of pathogen; b) the best temperature for mycelial growth in potato-dextrose-agar medium
(PDA) was 25oC; eight isolates exhibited response to the photoperiods used whereas six
were sensitive to photoperiod; the majority of isolates sporulated more under 24 hours of
light; eight hours of continuous humidity was enough to germinate the majority of spores
of the isolates; the pathogenicity of isolates was observed and some hosts were more
specifics to their isolate of origin, such as tomato plant, and others such as melon and
cotton plants were less specifics; and the mycelial growth of the great part of isolates were
not affected by the preservation method; sporulation showed great variation among the
methods and all preservation methods conserved the pathogenicity of the isolates; c) the
eletrophoresis analysis of sterase isozyme showed variation in number of the bands and
positions in the gel which indicated differences among isolates, these were divided in two
different groups of similarity, probably indicating the existence of races among them; d)
the less susceptible hybrids were Taisho, Nikkey, Yoshinari and Safira; the difenoconazole
fungicide resulted in better porcentage of pathogen inhibition in vitro and carbendazim
and thiophanate-methyl presented the worst results, and this last one can not be able to
inhibite the mycelial fungi growth and before seven and fourteen days of artificial
inoculation of pathogen and application of fungicides, only azoxystrobin was efficient to
control the disease.
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Citação
TERAMOTO, Adriana. Morphologic, physiologic, isozymic characterization of Corynespora
cassiicola (Berky & Curt) Wei, causal agent of target spot, and its control. 2008. 81 f. Tese (Doutorado em Ciências Agrárias) - Universidade Federal de Goiás, Goiânia, 2008.