Cândida Renata Jacobsen Farias

Qualidade sanitária de sementes de aveia-preta (Avena strigosa Schreb.) produzidas no estado do Rio Grande do Sul, safra 1999/2000

Este trabalho teve como objetivo avaliar a qualidade sanitaria de sementes de aveia-preta (Avena strigosa Schreb.) produzidas no Estado do Rio Grande do Sul. Foram avaliados 81 lotes de sementes oriundos de 16 municipios de diferentes regioes fisiograficas. Utilizou-se o metodo do substrato papel, com 400 sementes por lote. Foram detectados os fungos Alternaria sp., Chaetomium sp.,Cladosporium sp., Colletotrichum sp., Curvularia sp., Epicoccum sp., Nigrospora sp., Colletotrichum sp., Fusarium sp. e os fungos de armazenamento Aspergillus sp.e Penicillium sp.A maior incidencia media foi dos fungos Phoma sp.e Bipolaris spp., com 18,4 e 22,4% respectivamente. Pode-se concluir que deve haver um melhor manejo da cultura da aveia-preta, visando diminuir a contaminacao das sementes por fungos, principalmente, nas regioes tipicas produtoras de cereais de inverno.Uma das principais causas da baixa produtividade de milho e a qualidade da semente, que afeta o estande inicial, o vigor das plantas e, consequentemente, a produtividade. O objetivo deste trabalho foi determinar o efeito da germinacao, um dos principais componentes da qualidade da semente e a densidade de semeadura no estabelecimento da cultura e na produtividade de milho. Quatro lotes de sementes de milho hibrido BRS 201, com germinacao de 95%, 90%, 85% e 75%, foram semeados em tres densidades de semeadura: 50, 60 e 70 mil sementes/ha na Embrapa Milho e Sorgo, Sete Lagoas. MG, em 1996/97 e 1997/98. Os parâmetros avaliados foram: emergencia de plântulas 10 dias apos a semeadura, indice de velocidade de emergencia (IVE), numero de espigas/ha, numero de plantas/ha, producao de espigas/ha e producao de graos/ha. A utilizacao de sementes com germinacao inferior a 90% provocou reducoes acentuadas na emergencia de plântulas em campo, no numero de plantas e consequentemente, na produtividade do milho BRS 201. O aumento da densidade de 50 para 70 mil sementes/ha na semeadura nao compensou a reducao da qualidade de semente. Para o acrescimo de 15% na germinacao, foi observado, em media, um ganho de produtividade de 30%. Com base nos resultados deste trabalho, recomenda-se aos produtores de milho, a utilizacao de lotes de semente com germinacao superior a 90% e densidade de semeadura entre 50 e 60 mil sementes/ha.

Regional survey and identification of Bipolaris spp. associated with rice seeds in Rio Grande do Sul State, Brazil

In the harvest year of 2004, a random sample of seed lots (n=165) from six rice-growing regions of Rio Grande do Sul (RS) State, Brazil, were examined under seed health blotter test. Fungi growth resembling Bipolaris or Drechslera spp. was isolated and identified at the species level. Observations on the anamorphic structures (conidiophores and conidia) allowed separation of isolates into three groups. Pseudothecia, asci and ascospores from sexual crosses between isolates from a same anamorphic group but originated from different regions showed the typical characteristics of three recognized species (anamorph/ teleomorph): Bipolaris cynodontis (Cochliobolus cynodontis); B. curvispora (C. melinidis) and B. oryzae (C. miyabeanus). All species were widely distributed across the rice-growing regions. Overall, the most prevalent species were B. oryzae (44.6%) and B. curvispora (42,9%) followed by B. cynodontis (24,1%). This is the first report of B. cynodontis associated with rice seeds in Brazil and the preliminary identification of B. curvispora in rice by the observation of the teleomorph phase was confirmed. The regional occurrence of a complex of pathogenic Bipolaris species related to brown spot epidemics in other countries, may have epidemiological consequences in the region which deserve further investigation.

Infecção de sementes de trigo com Bipolaris sorokiniana pela técnica de restrição hídrica

Seed inoculation with pathogenic fungi using the water restriction technique is relatively recent. This study aimed to verify the effect of osmotic potentials (-0.4, -0.6 and -0.8 MPa) of PDA substrate modified by the amendment of sucrose in interaction with the period of exposure (48, 72 and 96 h) of wheat seeds to colonies of Bipolaris sorokiniana. Infection efficiency and inhibition of seed germination during and after treatment were the variables analyzed. The results of this study show that an exposure period longer than 48 hours to the fungal colonies did not inhibit full germination of the seeds. The germination rate increased linearly as the exposure period to the fungal colony was increased. Infection efficiency was not affected by osmotic potential and exposure time, varying from 0.53 to 0.92. However, seed germination was significantly reduced after 48 hours of exposure to the fungal colonies.

Regional and varietal differences in prevalence and incidence levels of Bipolaris species in Brazilian rice seedlots

A total of 722 rice seed lots were collected at six production regions of Rio Grande do Sul state during three consecutive seasons (2009/10 to 2011/12). For each seed lot, 200 seeds were assessed for the presence of Bipolaris spp. using a standard seed health blotter test. Results showed that B. oryzae and B. cynodontis were found in 62.5% and 10.4% of the seed lots, respectively. Overall mean incidence of B. oryzae and B. cynodontis were 0.5% and 0.06%, respectively. For the two most sampled varieties (75% of the seed lots), IRGA 424 and Puita INTA CL, mean incidence levels were highest and lowest, respectively. Among regions, infection risk was highest in the southeastern and lowest in the western regions of the state, especially the Fronteira Oeste. The prevalence and the incidence levels of Bipolaris oryzae reported in this study were lower than previous reports in the same region - eighty percent of the seed lots showed incidence levels below the recommended 5% inoculum threshold. In conclusion, rice seeds produced by IRGA-certified growers showed an overall good health quality with regards to B. oryzae infection, which is the main Bipolaris species associated with rice seeds in southern Brazil.

CONTROLE IN VITRO DE Bipolaris oryzae (Breda de Haan) COM EXTRATO DE Curcuma longa (Linnaeus) E SUA INTERFERÊNCIA NA FISIOLOGIA DAS SEMENTES DE ARROZ

This study was conducted to evaluate the use of Curcuma longa (Linnaeus) extract in the in vitro control of Bipolaris oryzae (Breda de Haan) and to characterize the effect of this extract on rice seed germination. A completely randomized arranged in a factorial experimental design was used: three isolates of B. oryzae from rice seed from different rice-growing regions of Rio Grande do Sul (Fronteira Oeste, Campanha, and Sul) were tested with three concentrations (20, 40, and 80 mg/mL) of C. longa plus a control treatment (0 mg/mL). Each reaction was repeated in quadruplicate. The effect of the extract upon the disease development was evaluated based on mycelial growth (PMG) and spore production; rice seed germination was evaluated using a germination test (Germitest®). The PMG results demonstrate that the treatments were effective in reducing PMG, with a stronger response observed as the concentration of the extract increased. An average inhibition of 84% of sporulation was observed for the tested strains compared with the control treatment. There were, however, no significant differences in terms of seed germination test with the different C. longa concentrations. Therefore, treatment of rice seeds with C. longa extract does not affect seed germination but positively inhibits mycelial growth and sporulation, affecting the in vitro sporulation of the different isolates of B. oryzae.

Ocorrência de Helicoceras oryzae em sementes e grãos de arroz produzidos no Rio Grande do Sul

Samples of rice seeds and grains were collected from different localities in the state of Rio Grande do Sul during 2000-2001 (62 samples) and 2001-2001 (194 samples). Samples from the localities of Agro Reis, Agudo, Alegrete, Arambare, Arroio Grande, Bage, Cacapava do Sul, Cachoeira do Sul, Cachoeirinha, Camaqua, Cangucu, Capao do Leao, Capivari do Sul, Dom Pedrito, Eldorado do Sul, Esteio, Guaiba, Herval, Itaqui, Julio Castilhos, Morro Redondo, Palmares do Sul, Pedro Osorio, Pelotas, Pinheiro Machado, Porto Alegre, Quarai, Restinga Seca, Rio Grande, Rosario do Sul, Santa Vitoria do Palmar, Santa Rita, Santo Ângelo, Santo Antonio, Sao Borja, Sao Gabriel, Sao Lourenco do Sul, Sao Luiz Gonzaga, Tapes, Turucu, Uruguaiana and Viamao were evaluated for the presence of a pest not found in Brazil, Helicoceras spp. Using the blotter test, 400 seeds were examined for each sample. The fungus H. oryzae was found in three samples of the 2000-2001 season: 268 (EEA-406), 647 (FORMOSA) and 652 (IRGA 419) from Cachoeirinha. These results allowed confirmation of the presence of the fungus H. oryzae. The Conesul Committee of Plant Health and Safety is evaluating the exclusion of this fungus, considered a pest of minor importance, from the quarantine list. Future studies about dissemination and impacts of the disease are necessary to support effective control measures.

Health quality of black oat (Avena strigosa Schreb.) seeds pruduced in Rio Grande do Sul statet

Este trabalho teve como objetivo avaliar a qualidade sanitaria de sementes de aveia-preta (Avena strigosa Schreb.) produzidas no Estado do Rio Grande do Sul. Foram avaliados 81 lotes de sementes oriundos de 16 municipios de diferentes regioes fisiograficas. Utilizou-se o metodo do substrato papel, com 400 sementes por lote. Foram detectados os fungos Alternaria sp., Chaetomium sp.,Cladosporium sp., Colletotrichum sp., Curvularia sp., Epicoccum sp., Nigrospora sp., Colletotrichum sp., Fusarium sp. e os fungos de armazenamento Aspergillus sp.e Penicillium sp.A maior incidencia media foi dos fungos Phoma sp.e Bipolaris spp., com 18,4 e 22,4% respectivamente. Pode-se concluir que deve haver um melhor manejo da cultura da aveia-preta, visando diminuir a contaminacao das sementes por fungos, principalmente, nas regioes tipicas produtoras de cereais de inverno.Uma das principais causas da baixa produtividade de milho e a qualidade da semente, que afeta o estande inicial, o vigor das plantas e, consequentemente, a produtividade. O objetivo deste trabalho foi determinar o efeito da germinacao, um dos principais componentes da qualidade da semente e a densidade de semeadura no estabelecimento da cultura e na produtividade de milho. Quatro lotes de sementes de milho hibrido BRS 201, com germinacao de 95%, 90%, 85% e 75%, foram semeados em tres densidades de semeadura: 50, 60 e 70 mil sementes/ha na Embrapa Milho e Sorgo, Sete Lagoas. MG, em 1996/97 e 1997/98. Os parâmetros avaliados foram: emergencia de plântulas 10 dias apos a semeadura, indice de velocidade de emergencia (IVE), numero de espigas/ha, numero de plantas/ha, producao de espigas/ha e producao de graos/ha. A utilizacao de sementes com germinacao inferior a 90% provocou reducoes acentuadas na emergencia de plântulas em campo, no numero de plantas e consequentemente, na produtividade do milho BRS 201. O aumento da densidade de 50 para 70 mil sementes/ha na semeadura nao compensou a reducao da qualidade de semente. Para o acrescimo de 15% na germinacao, foi observado, em media, um ganho de produtividade de 30%. Com base nos resultados deste trabalho, recomenda-se aos produtores de milho, a utilizacao de lotes de semente com germinacao superior a 90% e densidade de semeadura entre 50 e 60 mil sementes/ha.