Supressão de brusone nas folhas de arroz com Cladosporium cladosporioides.
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2014-02-21
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Universidade Federal de Goiás
Resumo
Rice blast (Magnaporthe oryzae Couch, anamorph-Pyricularia oryzae Cav.) is
the major disease of rice causing yield losses up to 100%, in the world. Its control,
currently held by integrating genetic resistance, cultural practices and chemical control,
requires the inclusion of biological agents. The objectives of this study were to evaluate the
in vitro antagonism between C. cladosporioides and four different rice pathogens; to verify
the ability of C. cladosporioides in suppressing leaf blast and to study the mechanisms
involved during disease suppression. The bioassays were conducted in a completely
randomized design with three replications. The antagonism in vitro was evaluated by
pairing-up, in Petri dishes containing PDA medium, nine different isolates of C.
cladosporioides with the rice pathogens Sarocladium oryzae (sheath rot), Monographella
albescens (scald), Cochliobolus miyabeanus (brown stain) and M. oryzae. All C.
cladosporioides isolates reduced colonies mycelia growth up to 53.84% in addition to hallo
formation. Among the nine tested isolates, four were selected for in vivo studies. Under
controlled greenhouse conditions, three different concentrations were tested, in two
different applications way; 1) 48 hours before challenger inoculation with M. oryzae; 2)
mixture of M. oryzae and C. cladosporioides conidia suspensions. The isolated C24 C.
cladosporioides (5x105) sprayed 48 hours, before challenger inoculation reduced 97.1% of
leaf blast severity, and the spray mixture of conidial suspensions of C24 C. cladosporioides
(5x101) and M. oryzae 3x105 spray of decreased leaf blast severity by 88.6%.
Subsequently, the mechanisms involved in leaf blast suppression were investigated by
using the same isolate, both applications methods and by collecting rice plants leaves
sprayed with C. cladosporioides and M. oryzae. The application of C. cladosporioides 48
hours before challenger inoculation with M. oryzae and the conidial suspensions of mixture
of M. oryzae and C. cladosporioides reduced to 83.9% and 78.6% of leaf blast severity,
respectively. It was detected that, in the presence of C. cladosporioides and absence of the
pathogen activity of enzymes GLU, LIPOX, PAL and POX increased significantly. In the
presence of, C. cladosporioides and M. oryzae, POX and PAL activity and AS content also
significantly increased, in both application forms. Scanning electron microscopy confirmed
the physical interaction between plant/biological agent/pathogen during the penetration
phase. It was proved that C. cladosporioides is a biological agent efficient in activating
biochemical defense mechanisms of the rice plant during leaf blast suppression.
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CHAIBUB, A. A. Supressão de brusone nas folhas de arroz com Cladosporium cladosporioides.. 2014. 79 f. Dissertação (Mestrado em Agronomia) - Universidade Federal de Goiás, Goiânia, 2014.