Valácia Lemes da Silva Lobo

An Unprecedented Outbreak of Rice Blast on a Newly Released Cultivar BRS Colosso in Brazil

Rice blast occurred in epidemic proportions on a newly released upland rice cultivar BRS Colosso, in the rice growing season 2004/2005. Twenty isolates were collected from the affected panicles of the cultivar BRS Colosso from three different States, two pathotypes IB-1 and IB-17 were identified. They were classified into thirteen Brazilian pathotypes based on the reaction pattern on eight upland rice cultivars, utilized as local differentials. Differences in aggressiveness of the isolates on the cultivar BRS Colosso were evident. Ten highly aggressive isolates were used to determine the partial resistance to leaf blast in the BRS Colosso and BRS Bonanca. There was no significant isolate x cultivar interaction for partial resistance. The mean leaf blast severity was significantly higher in BRS Colosso than in BRS Bonanca. Inoculation of culms with the same ten isolates showed cultivar x isolate interaction. Some isolates were more aggressive showing severe culm blast. There was no correlation among the aggressiveness of the isolates on leaf and culm. The disease outbreak in BRS Colosso could be attributed to the absence of adequate degree of partial resistance, the preexistence of compatible pathotypes IB-1 and IB-17 and their dissemination through seed.

Stability and microbiological quality of rice bran subjected to different heat treatments

Rice bran is a byproduct commonly used for animal feeding; however its nutritional value and potential application in human diet have attracted market interest. Its preservation for safe use is still a challenge, so the objective of this study was to determine the quality of commercially available rice bran samples subjected to different heat treatments (extruding, parboiling, toasting, and microwave oven heating) in order to promote stabilization during storage under room temperature. Rice bran samples were collected from two industries, and each treatment was divided in three parts, each corresponding to three repetitions. All samples were evaluated for moisture content, total microorganisms, mold and yeast counting, hydrolytic rancidity, and lipase activity during 90 days of storage. Most of the heat treatments, including domestic and thermoplastic extrusion, generated products which may be used for human consumption under the tested conditions in terms of physicochemical and microbiological quality. The domestic treatments were more efficient in eliminating microorganisms or keeping them within acceptable limits. The toasted rice bran showed satisfactory results in terms of moisture, hydrolytic rancidity control, and lipase activity.

Efeito do tratamento químico de sementes de arroz no controle da brusone nas folhas e na qualidade sanitária e fisiológica das sementes

Foram realizados dois experimentos de campo, em 2004 e 2005 com o objetivo de avaliar a eficiencia de fungicidas no tratamento de sementes no controle de brusone nas folhas. Os mesmos fungicidas foram avaliados em laboratorio, analisando-se o perfil fisiologico e sanitario das sementes tratadas. A analise conjunta dos experimentos mostrou diferencas significativas quanto aos valores da area abaixo da curva de progresso da doenca (AACPD). Os tratamentos com pyroquilon e azoxystrobin foram os que propiciaram menor severidade de brusone nas folhas, apresentando as menores AACPD, enquanto o tratamento com carboxim + thiram nao diferiu da testemunha no controle da doenca. No entanto, este tratamento aumentou significativamente a germinacao das sementes em relacao a testemunha (22%) e aos demais tratamentos. De maneira geral, todos os tratamentos foram eficientes em reduzir e/ou eliminar os fungos presentes nas sementes em laboratorio, o carboxin + thiram e o tricyclazole foram os tratamentos que se destacaram.

Use of local rice cultivars as additional differentials to identify pathotypes of Pyricularia oryzae

Eight additional rice cultivars as differentials were selected to identify pathotypes occurring in the Tocantins State. They were BRS Jaburu, BRS Taim, BRS Bigua, BR IRGA-417, Epagri 109, Javae, Metica-1 and Supremo. These differentials were used in addition to the international set to determine the pathogenic diversity of 193 Pyricularia oryzae isolates collected during 1994-2002 from irrigated rice cultivars. They were conserved in Pyricularia culture collection of Embrapa Rice and Bean Research center. From 193 P. oryzae isolates 38 pathotypes were identified based on leaf blast reactions of international set and 29 pathotypes based on these additional differentials. The predominant pathotypes (TI-1, TG-2, TD-15 and TF-2) were represented by 53% of the tested isolates. The major international pathotypes (IB-45, IB-41, II-1 and ID-13) were represented by 43% of the isolates tested. The virulence pattern of 28 isolates belonging to the pathotype IB-45 was further differentiated into nine local pathotypes using additional set of differentials. The irrigated rice cultivars used as additional differentials serve as complementary set to identify pathotypes of interest for breeding blast resistant cultivars for Tocantins State.

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.