A New Gene in Maize Conferring the "Chlorotic Halo" Reaction to Infection byExserohilum turcicum

During recurrent selection in the maize synthetic BS19, S 1 lines exhibiting a unique lesion phenotype in response to infection with Exserohilum turcicum were observed. This phenotype, dubbed chlorotic halo, initially appears as dark orange-brown pigmented infection points that are later surrounded by a circular chlorotic halo about 1 cm in diameter. Most infection points retain this phenotype, although some later develop into the elongated, elliptical necrotic lesions typical of northern leaf blight (NLB). An inbred line derived from this initial selection was crossed to the susceptible inbred line A619 and the inheritance of the chlorotic halo reaction studied in advanced generations from this cross. Segregation ratios were consistent with the hypothesis that the chlorotic halo phenotype is controlled by a single recessive gene. This gene appears to be located on the short arm of chromosome 1 near the centromere, based upon reciprocal translocation mapping studies. The chlorotic halo reaction was expressed against races 0,1,23, and 23N of E. turcicum in the field. The effectiveness of the chlorotic halo gene in reducing losses to NLB remains to be demonstrated.