Reactions of supersweet (sh2) sweet corn to northern leaf blight (NLB)
and associated yields were evaluated in Belie Glade, Florida and Urba
na, Illinois in yield-loss trials, hybrid evaluations, and evaluations
of breeding materials. Hybrids differed significantly for NLB in all
trials. Severity of NLB ranged from 0 to 66% on 35 sh2 hybrids in yiel
d-loss trials, and from 0 to 60% on 80 sh2 hybrids in hybrid evaluatio
ns. NLB ratings ranged from 1 to 9 (approximately 0 to 80% severity) o
n 375 hybrids and 186 inbred lines in evaluations of breeding material
s. Various methods of rating NLB and ratings from multiple dates were
highly correlated, with correlation coefficients ranging from 0.76 to
0.98. Yield, measured as weight of ears and number of marketable ears
from inoculated plots as a percentage of that from control plots, decr
eased as disease severity increased. Linear or quadratic regression mo
dels explained 31 to 70% of the variation in percent yield as a functi
on of disease severity at harvest. The effects of NLB on yield were li
mited by NLB-resistance in several hybrids, including CCO 3268, Chieft
ain, Crisp N Sweet 710A, Day Star, Envy, Forever, GSS 1526, Jupiter, M
idship, Prime Plus, Sch 5005, and SummerSweet 7630. Although high leve
ls of partial resistance to NLB were prevalent among 375 new experimen
tal sh2 hybrids and 186 sh2 inbred lines evaluated in 1995, use of the
gene HtN may increase in the near future as breeders are incorporatin
g this resistance into new inbreds and hybrids. Breeders and plant pat
hologists would be wise to continue improving partial resistance to NL
B without using the gene HtN in genotypes with adequate levels of part
ial resistance, because the widespread use of the gene HtN will select
for virulent races of Exserohilum turcicum which occur in Florida, or
for races with new combinations of virulence.