Avaluation of Methods of inoculation of Gibberella zeae in maize

O plantio direto e o cultivo de milho safrinha sÃo fatores que podem proporcionar alteraÃÃes no microclima e na biologia do agroecossistema, aumentando as populaÃÃes de fungos como Gibberella zeae, agente etiolÃgico da doenÃa denominada giberela ou podridÃo-vermelha-da-espiga. Esse trabalho teve como objetivo identificar mÃtodos de inoculaÃÃo que auxiliassem na seleÃÃo e na caracterizaÃÃo de genÃtipos tolerantes à G. zeae. O experimento foi conduzido no municÃpio de Toledo/PR durante a safrinha de 2008. O delineamento experimental foi em blocos ao acaso com cinco repetiÃÃes, em esquema fatorial tendo como primeiro fator os hÃbridos (2B710; 30F45; DKB 214; 30F98; DKB 390; AG 9020; 30F80; 30R50 e 30K73) e como segundo fator os mÃtodos de inoculaÃÃo. Os hÃbridos foram agrupados como suscetÃveis (2B710; 30F45; DKB 214; 30K73), tolerantes (DKB 390; AG 9020; 30F80; 30R50) e moderadamente suscetÃvel a giberela (30F98). Os 12 mÃtodos avaliados consistiam em simular a infecÃÃo natural do fungo pelo estigma ou por danos causados por insetos nas laterais das espigas, variando ainda em ausÃncia de cobertura (cÃmara Ãmida), cobertura por 24 horas e por 48 horas. Os mÃtodos com inoculaÃÃo de 2 mL na lateral da espiga sem cobertura (3), com cobertura por 24 horas (7) e com cobertura por 48 horas (11) se mostraram eficientes na caracterizaÃÃo de hÃbridos tolerantes e suscetÃveis e poderÃo ser empregados em larga escala na identificaÃÃo e seleÃÃo de variedades de milho tolerantes à doenÃa. Mais do que isso, a sociedade poderà consumir produtos de milho com qualidade superior, com menos micotoxinasThe non tillage planting and the cultivation of âsafrinhaâ (short season) corn are factors that may provide alterations in the microclimate and in the biology of agro ecosystem, increasing the populations of fungus like Gibberella zeae, which is the etiologic agent of one of the maize ear rots. This work had the objective to identify inoculation methods that can be useful in the election and in the characterization of genotypes tolerant to G. zeae. The experiment was conducted in Toledo/PR during the 2008 âsafrinhaâ season in a randomized complete block design with five replications, on a factorial scheme where hybrids were the first factor (2B710; 30F45; DKB 214; 30F98; DKB 390; GAC 9020; 30F80; 30R50 and 30K73) and the inoculation methods were the second factor. The hybrids had been grouped as susceptible (2B710; 30F45; DKB 214; 30K73), tolerant (DKB 390; GAC 9020; 30F80; 30R50) and moderately susceptible to giberela (30F98). The 12 evaluated methods consisted of simulating the fungus natural infection on the silk or on the damage caused by insects in the lateral of the ears, and also varying by the absence of covering on the ear (humid chamber), by covering the ear for 24 hours and by covering the ear for 48. The methods with inoculation of 2 mL in the lateral of the ear without covering (3), with covering for 24 hours (7) and with covering for 48 hours (11) had shown efficiency in the characterization of tolerant and susceptible hybrids and could be used on a large scale in the identification and selection of maize varieties with tolerance to ear rot caused by G. zeae. As a result, the seed industry can provide superior materials and the farmers will reduce their losses due to kernel quality. Moreover, the whole society will consume better maize products, with less mycotoxin