Keywords: Maize genotype, Nothern leaf blight, tolerance

Northern leaf blight caused by Helminthosporium turcicum (synonym; Exserohilum turcicum) is a major disease of maize and threatening to maize production especially in the hills of Nepal. Cultivation of resistant/tolerant variety is only the practical, economical and feasible way of managing this disease, though other means of disease control particularly chemicals have been reported as effective to suppress the disease. Lack of resistant/tolerant varieties or gradual resistance breakdown of released varieties necessitates the continuous research on Helminthosporium pathogen in order to increase the frequency of resistance genes in maize genotypes. Therefore, pathogenic isolate of Helminthosporium turcicum was collected from hills and terai regions and evaluated for their virulence. Host genotypes were evaluated by using most virulent isolate of pathogen and resistance was assessed based on area under disease progress curve (AUDPC), experimented in green house and field at different locations: National Maize Research Program, Rampur (2000 winter), Institute of Agriculture and Animal Science, Rampur (2001 winter; and at Lumle Agricultural Research Station, Lumle (2000, summer) in randomized complete block design with three replications. Among the genotypes evaluated, Population 22, BA 93/2126, Across 94502, Rampur composite, Yellow hill pool, Across 9244, Population 42 C₈ and White hill pool performed better against Northern leaf blight compared to other genotypes. Moreover, leaf spot appeared late in Population 22, as described in HtN. BA 93/2126 also exhibited similar trend indicating tolerance/resistance source for Helminthosporium turcicum. Kalipare Panhelo, Yellow popcorn and White popcorn had always higher AUDPC and disease severity indicating potential sources for spreader rows in evaluating northern leaf blight breeding program/nursery.