Gray Leaf Spot Disease of Maize: Rating Methodology and Inbred Line Evaluation

Abstract

Development of gray leaf spot (GLS) of maize (Zea mays), caused by Cercospora zeae-maydis, was evaluated in seven inbreds in 1990 and 19 inbreds in 1991 in field plots with naturally infested corn debris. In 1990, nine ratings over 35 days were made beginning 9 August. In 1991, 10 ratings over 43 days were made beginning 17 July. Individual plants were assessed by two methods: 1) a disease index (DI) score was assigned on a 1-5 scale (1=no lesions, 5=all leaves dead); and 2) disease severity (DS) was expressed as diseased leaf area divided by the total area multiplied by 100, assessed on the ear -1 leaf and all leaves above it. The mean of ratings over time and the area under the disease progress curve (AUDPC) rankings for seven inbreds were similar both years (.)