RESISTANCE TO NORTHERN LEAF-BLIGHT IN MAIZE (ZEA-MAYS) CONDITIONED BYTHE HTN GENE AND THE ASSOCIATION WITH ISOPEROXIDASES

The Htn gene confers resistance to northern leaf blight (NLB) caused b y Exserohilum turcicum. Three maize (Zea mays) near isogenic lines (NI Ls), with and without the gene HtN, two sweet corn inbred lines (IL677 a and H6314Htn), together with the parental, F1, F2, and backcross1 (B C1) populations from a cross between the inbreds W64A and W22HtN, were artificially inoculated and evaluated in the greenhouse for comparati ve resistance to race 1 of E. turcicum. The number and the size of les ions developed on the genotypes carrying the HtN allele were significa ntly reduced in comparison with plants lacking the HtN allele. Resista nce of plants carrying HtN was characterized by the formation of yello w or red spots at and around the sites of inoculation. Greenhouse stud ies were confirmed by field experiments. The association between isope roxidases and HtN gene was studied in leaf tissue samples which were c ollected from seedlings of the parents, F1, BC1, and F2 HtN segregatin g populations, prior to inoculation. Polyacrylamide gel electrophoresi s revealed distinct isoperoxidases for the susceptible and for the res istant inbred lines. A strong correlation was observed between individ ual plant-specific isozymes and plant expression of resistance conferr ed by the HtN allele in the segregating BC1 and F2 populations. These results suggest that, in the resistant parent, the HtN gene is linked to a locus coding for a specific isoperoxidase, or that the gene produ ct of the HtN allele is this isoperoxidase itself. The potential use o f peroxidase isozyme analysis as a marker for HtN is discussed.