Márcio Vinícius Carvalho Barros Côrtes

Increased enzymatic activity in rice leaf blast suppression by crude extract of Epicoccum sp

Epicoccum sp. showed in vitro antagonism to the rice pathogens Magnaporthe oryzae, Rhizoctonia solani, Sarocladium oryzae, Monographella albescens and Cochliobolus miyabeanus in dual culture. The colony growth of the rice blast fungus, M. oryzae, was reduced by 42.50%. The lethal doses (LD50) determined based on probit-log dosage response curves at 3 and 6 hours after germination were 393.0 and 326.6 ppm, respectively. The crude extract (600 ppm) reduced appressorial formation by 95.68%. A greenhouse experiment comparing the relative efficiency of conidial suspension and crude extract of Epicoccum sp. in the suppression of leaf blast showed no statistical difference between both application methods. However, the crude extract of Epicoccum sp. (4000 ppm) 48 hours before the application of M. oryzae induced resistance and suppressed leaf blast by 97.6%. Scanning electron microscopy of rice leaves inoculated with crude extract of Epicoccum sp. and challenged with M. oryzae showed appressorial deformation on penetration phase. Peroxidase and β-1,3-glucanase activities increased in plants sprayed with crude extract of Epicoccum sp., 24 hours after the application of the challenger. PAL as well as chitinase activities increased 72 hours after challenge inoculation. Epicoccum sp. was shown to be a potential antagonist and inducer of resistance against M. oryzae.

Characterization of Sarocladium oryzae and its reduction potential of rice leaf blast

1. Manuscript received in Aug./2016 and accepted for publication in Mar./2017 (http://dx.doi.org/10.1590/1983-40632016v4742738). 2. Universidade Federal de Goiás, Escola de Agronomia, Goiânia, GO, Brazil. E-mail: rafaela_argui@hotmail.com. 3. Empresa Brasileira de Pesquisa Agropecuária (Embrapa Arroz e Feijão), Laboratório de Microbiologia Agrícola, Santo Antônio de Goiás, GO, Brazil. E-mails: valacia.lobo@embrapa.br, marcio.cortes@embrapa.br, cristina.filippi@embrapa.br, prabhu.anne@colaborador.embrapa.br. The integrated management of rice leaf blast (Magnaporthe oryzae) is carried out mainly with the adoption of chemical control. However, the search for alternative practices has grown in recent years. Thus, the variability of 28 Sarocladium oryzae isolates was evaluated for the cerulenin production, as well as its potential for reducing the severity of rice leaf blast, quantifying the activity of enzymes linked to the plant defense mechanisms. More than 55 % of the S. oryzae isolates were antagonistic to the pathogens M. oryzae, Cochliobolus miyabeanus, Thanatephorus cucumeris and Monographella albescens, and 60 % of the isolates produced cerulenin at detectable levels. Both BRM 6461 (296.0 μg mL-1) and BRM 6493 (undetectable cerulenin) inhibited the formation of M. oryzae appressoria in 89.5 % and 85 %, respectively. The BRM 6461 isolate, applied as conidial suspension and filtered, reduced the severity of rice leaf blast in 68.8 % and 75.5 %, respectively. The enzymatic activity in the presence of M. oryzae was higher for lipoxygenase at 5 h (filtered) and at 24 h and 72 h (conidial suspension) after the pathogen inoculation. For phenylalanine ammonia lyase, the highest expression was at 5 h (filtered) and 72 h (conidial suspension). The enzymes chitinase, β-1,3glucanase and peroxidase and the salicylic acid phytohormone presented no differences, in relation to the controls (water and M. oryzae). The filtered from the BRM 6461 isolate, basically constituted by cerulenin, reduced the severity of rice leaf blast and possibly activated the defense mechanisms of the rice plants against M. oryzae.