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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.2019.tde-20191218-115631
Document
Author
Full name
Andrea Carla Krambeck da Silva Santos
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1995
Supervisor
Title in Portuguese
Fusarium oxysporum f. sp. vasinfectum em sementes de algodoeiro: detecção, inoculação artificial e controle químico
Keywords in Portuguese
ALGODÃO
FUNGICIDAS
FUNGOS FITOPATOGÊNICOS
INOCULAÇÃO
MURCHA DE FUSARIUM
SEMENTES
Abstract in Portuguese
A murcha de Fusarium do algodoeiro, causada por Fusarium oxysporum f. sp. vasinfectum (Atk) Snyder & Hansen, é uma das doenças mais importantes da cultura. Quando não se dispõe de cultivares resistentes, o seu controle deve envolver o emprego de sementes livres do patógeno e/ou o tratamento sistemático de sementes com fungicidas altamente eficientes, para minimizar a possibilidade de introdução do fungo em áreas isentas. Sementes da cultivar suscetível Acala Del Cerro, produzidas em região onde a doença tem ocorrido com frequência, foram utilizadas no presente trabalho. Foram comparados cinco métodos de detecção de Fusarium oxysporum f. sp. vasinfectum em sementes: papel de filtro, papel de filtro com congelamento, papel de filtro com dicloran, meio BDA e meio PCNB. Considerando a recuperação de Fusanum oxysporum f. sp. vasinfectum e a inibição de Rhizopus sp., contaminante frequentemente associado às sementes e que mascara os resultados, determinou-se como sendo o método mais recomendado o do papel de filtro com congelamento. Como a incidência natural do patógeno em sementes é normalmente baixa (< 2 % ), determinou-se o método mais adequado de inoculação artificial de sementes, para se dispor de material infectado, em grande quantidade, em condições semelhantes às ocorridas na natureza, para a realização de testes in vivo. Foram comparados cinco variações do método de contato das sementes com a colônia do patógeno. Verificou-se que 48 horas de contato, a 20 ± 2°C, 12h luz/12h escuro, proporcionou 99,33% de sementes infectadas, que mantiveram suas condições fisiológicas satisfatórias. A sensibilidade de Fusarium oxysporum f. sp. vasinfectum aos fungicidas foi determinada através de testes in vitro e in vivo. Onze tratamentos (fungicidas e misturas) foram comparados quanto a percentagem de inibição do crescimento micelial (PIC), através de medição do diâmetro de colônia em BDA com 0,1; 1; 10 e 100 ppm do produto. Através do cálculo do ED50 (concentração que inibe em 50% o crescimento micelial), foram considerados altamente eficientes (ED50 < 1 ppm) prochloraz, thiabendazol, benomyl, thiabendazol + thiram e benomyl + thiram; comportaram-se como pouco eficientes (ED50 = 10-50 ppm) carboxin + thiram, captan e thiram; foram ineficientes (ED50 > 50 ppm) dicloran, carboxin e PCNB. No teste in vivo, sementes de algodoeiro inoculadas artificialmente com Fusarium oxysporum f. sp. vasinfectum foram submetidas ao tratamento com os seguintes fungicidas e/ou misturas: benomyl (100 g i.a./100 kg sementes), thiabendazol (180 g i.a./100 kg), prochloraz (50 g i.a./100 kg), benomyl + thiram (50 + 140 g i.a./100 kg) e carboxin + thiram (187,5 + 187,5 g i.a./100 kg). Na testemunha, a incidência de Fusarium oxysporum f. sp. vasilifectum foi 100% no teste de sanidade pelo método do papel de filtro com congelamento; os tratamentos benomyl; prochloraz e benomyl + thiram, que não diferiram entre si, apresentaram controle superior a 94%; a mistura caboxin + thiram apresentou eficiência em torno de 50%. O tratamento com thiabendazol foi perdido devido a severa incidência de Rhizopus sp. Entretanto, o teste padrão de germinação e a emergência em areia mostraram melhor desempenho de benomyl + thiram, prochloraz e carboxin + thiram. Assim sugere-se que sementes comerciais de algodoeiro, suscetíveis a Fusarium oxysporum f. sp. vasinfectum, sejam tratadas com benomyl + thiram, na dose de 50 + 140 g i.a./100 kg de sementes
Title in English
Fusarium oxysporum f. sp. vasinfectum in cotton seeds: detection, artificial inoculation and chemical control
Abstract in English
The cotton Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (Atk) Snyder & Hansen, is one of the most important diseases of this crop. When resistant cultivars are not available, the disease control must involve the use of seeds free of the pathogen and/or sistematic seed treatment with highly efficient fungicides, to minimize the possibility of pathogen introduction in uninfested areas. Seeds of the susceptible cultivar Acala Del Cerro, produced in a region where the disease has occurred frequently, were used in this work. Five seed-borne Fusarium oxysporum f. sp. vasinfectum detection methods were compared: blotter, deep-freezing, blotter + dicloran, PDA medium and PCNB medium. Considering the Fusarium oxysporum f. sp. vasinfectum recovering and the contaminant Rhizopus sp. inhibition, the deep-freezing method was the recomended one. As the natural incidence of Fusarium oxysporum f. sp. vasinfectum in cotton seeds is normally low (< 2 %), the most adequate method for artificial inoculation, for obtaining a great amount of infected material similar to natural infection, necessary to in vivo tests was determined. Five variations of seed-colony contact method were compared. It was observed that the contact for 48 hours, at 20 ± 2°C, 12h light/12h darkness, produced 99,33% of infected seeds, wich keep their physiological conditions in a good level. The Fusarium oxysporum f. sp. vasinfectum sensibility to fungicides was measured by in vitro and in vivo experiments. Eleven treatments (fungicides and mixtures) were compared for the percentage of mycelial growth inhibition (PIC), through the measurement of the colony diameter in PDA with 0.1, 1,10 and 100 ppm of the products. Calculation of ED50 (fungicide concentration that reduce the mycelial growth in 50%) allows to consider as highly efficient (ED50 < 1 ppm) prochloraz, thiabendazol, benomyl, thiabendazol + thiram and benomyl + thiram; low efficient (ED50 = 10-50 ppm) were carboxin + thiram, captan and thiram; inefficient (ED50 > 50 ppm) were dicloran, carboxin and PCNB. For the in vivo assays, artificially Fusarium oxysporum f. sp. vasinfectum inoculated cotton seeds were submitted to the following fungicides and/or mixtures: benomyl (100 g a.i./100 kg seeds) , thiabendazol (180 g a.i./100 kg), prochloraz (50 g a.i./100 kg), benomyl + thiram (50 + 140 g a.i./100 kg) and carboxin + thiram (187.5 + 187.5 g a.i./100 kg). In the control, the Fusarium oxysporum f. sp. vasinfectum incidence was 100% in the seed health test by the deep freezing method; the treatments benomyl, prochloraz and benomyl + thiram, which did not differ among themselves, presented a control higher than 94 %; the carboxin + thiram mixture showed efficiency around 50%. The thiabendazol treatment was lost due to severe Rhizopus sp. incidence. However, the standard germination test and the germination in sand showed better performance of benomyl + thiram, prochloraz and carboxin + thiram. So, it is suggested that commercial cotton seeds, susceptible to Fusarium oxysporum f. sp. vasinfectum, could be treated with benomyl + thiram, 50 + 140 g a.i./100 kg of seeds
 
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Publishing Date
2019-12-19
 
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