EFFECTS OF RACE-0 AND RACE-1 OF EXSEROHILUM-TURCICUM ON SWEET CORN HYBRIDS DIFFERING FOR HT- AND PARTIAL RESISTANCE TO NORTHERN LEAF-BLIGHT

Field studies were done in 1988, 1989, and 1990 to compare the effects of races 0 and 1 of Exserohilum turcicum on sweet corn hybrids with different levels of Ht- and partial resistance to northern leaf blight (NLB). NLB decreased yields of susceptible hybrids in spite of chlorotic lesions, conditioned by Ht-resistance; but NLB had little effect on yields of hybrids with partial resistance. High levels of partial resistance in hybrids with or without Ht genes limited disease severity. Yields of partially resistant Ht-hybrids were within 10% of and not different from noninoculated controls. Yields of partially resistant hybrids without the gene Ht1 were not different from controls except for one comparison. Severity of NLB was less than 20% on partially resistant hybrids with or without Ht-genes and greater than 19% for hybrids that did not have partial resistance. Yields of susceptible hybrids without the gene Ht1 were 6-51% less than controls and did not differ between plots inoculated with races 0 or 1. Yields of susceptible hybrids with the gene Ht1 were 6-18% less than controls and did not differ between plots inoculated with races 0 or 1.