A NEW GENE IN MAIZE CONFERRING THE CHLOROTIC HALO REACTION TO INFECTION BY EXSEROHILUM-TURCICUM

During recurrent selection in the maize synthetic BS19, S-1 lines exhi biting a unique lesion phenotype in response to infection with Exseroh ilum turcicum were observed. This phenotype, dubbed ''chlorotic halo,' ' initially appears as dark orange-brown pigmented infection points th at are later surrounded by a circular chlorotic halo about 1 cm in dia meter. Most infection points retain this phenotype, although some late r develop into the elongated, elliptical necrotic lesions typical of n orthern leaf blight (NLB). An inbred line derived from this initial se lection was crossed to the susceptible inbred line A619 and the inheri tance of the chlorotic halo reaction studied in advanced generations f rom 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 stu dies. The chlorotic halo reaction was expressed against races 0,1,23, and 23N of E. turcicum in the field. The effectiveness of the chloroti c halo gene in reducing losses to NLB remains to be demonstrated.