A Method for Colletotrichum graminicola Inoculation in Maize Stalks

Abstract

ABSTRACT – Anthracnose stalk rot (ASR) disease caused by Colletotrichum graminicola can lead to major corn yield losses in Brazil. Studies on plant resistance and genetic variation in pathogen populations are required towards the development of ASR disease management strategies. However, the lack of adequate methods for C. graminicola inoculation in maize stalk has hindered these efforts. The main objective of the study was to develop a confident and feasible method for C. graminicola inoculation into maize stalk. Three inoculation methods were evaluated: TCMP (toothpick colonized by pathogen mycelium), TICS (toothpicks immersed in conidial suspension), and ICS (injection of conidial suspension). The effect of the internode position, the phenological stage, and the period of time required for maize reactions to ASR infection were also evaluated. The infection severity was assessed by a diagrammatic scale with six levels of severity from 0 (no necrotic spots) to 5 (100 % infection). The TICS was the best method, inoculation in the third internode and assessment of disease severity at tasselling stage (VT) 30 days after inoculation presented the more accurate results. The procedure was validated under field conditions. Key words: Zea mays; stalk rot; anthracnose. METODO PARA INOCULACAO DE Colletotrichum graminicola EM COLMOS DE MILHO RESUMO – A podridao do colmo do milho causada por Colletotrichum graminicola causa perdas severas em lavouras de milho. Estudos com resistencia de plantas e variabilidade genetica do patogeno sao necessarios para o desenvol-vimento de estrategias de manejo desta doenca. Por outro lado, ha ausencia de uma metodologia adequada para a inoculacao de C. graminicola em colmos. O objetivo principal do trabalho foi estabelecer uma metodologia confiavel e pratica para a inoculacao de C. graminicola. Foram avaliados tres metodos de inoculacao em colmo: palitos de dente colonizados por micelio; palitos de dente imersos em suspensao de conidios; e injecao de suspensao de conidios. Nos tambem determinamos o efeito da posicao do entreno inoculado, o estadio fenologico para a inoculacao e o periodo de tempo ideal apos a inoculacao para avaliar a severidade da doenca. O metodo de palitos de dente imersos em suspensao de conidios inoculado no terceiro entreno no estadio fenologico de pendoamento (VT) e avaliado aos 30 dias apos a inoculacao obteve o melhor resultado. A metodologia foi validada em plantas cultivadas em condicoes de campo. Palavras-chave: Zea mays; podridao de colmo, antracnose.