In this study, the same 98 lines used in
the study by Perkins and Hooker (6) were
evaluated at three locations (Iowa, Illinois, and Pennsylvania) with an
indigenous isolate of F. turcicum race 2 from that location. Thirty-five lines were
resistant, intermediate, or segregating for resistance at one or more locations.
Differences among locations for disease
reaction may have been due to variation
among isolates of F. turcicum race 2,
environmental effects, or differences
among evaluators. Plants in Iowa and
Illinois were rated by the same individual
but the plants in Pennsylvania were rated
by a different individual. However, the
rating was qualitative and the presence of
a chlorotic margin indicated a resistant
or intermediate-type lesion. Therefore, it
is possible that different individuals could
greenhouse. However, Ladyfinger pop
corn, an original source of resistance to
race 1 (3), was resistant at all locations
but was rated 5.9 in the greenhouse. A
number of lines that were rated 3.0
(resistant) in the greenhouse were
susceptible at one or more locations. The
differences in field and greenhouse
reactions may have been due to environmental differences (light, temperature,
relative humidity, etc.), growth stage of
the plants, or differences among isolates
of E. turcicum race 2. The isolate of E
turcicum used by Perkins and Hooker (6)
and the isolates used in this study were all
designates race2, i.e., virulent on plants
carrying the Ht gene. However, these
isolates may differ for other virulence
genes that have not been described.
According to these data, several
additional sources of chlorotic-type
lesion resistance are available for control
of E. turcicum race 2. It also appears that
with more differential cultivars, additional
races of E. turcicum may be described.