Agriculture Reference
In-Depth Information
dISEASE rESISTAnCE TESTS
A pathogen inoculation test can be easily used to distinguish between disease-resistant and disease-suscep-
tible crop varieties that otherwise appear similar. The test has been successfully used to distinguish between
Phytophthera-resistant and susceptible soybean varieties (Fig. 9.27) and also in corn hybrids with different
responses to southern corn leaf blight, for example, Texas male sterile lines versus normal cytoplasm lines.
Testing of varieties for resistance or susceptibility to a pathogen must take place under strictly controlled
conditions. Environmental factors, namely temperature, light, and relative humidity must be carefully con-
trolled. Maintaining suficient inoculum levels is critical for the success of the test. Stage of plant develop-
ment at which inoculation should take place is another critical factor in this type of test. For most species,
the seedling stage is the time of greatest susceptibility and is therefore ideal for inoculation. Although test
results may not always correlate with resistance under ield conditions, disease response is an accurate way
of distinguishing resistant varieties from susceptible ones.
Figure 9.27. A test for resistance to
Phytophthora
root rot in soybean. The variety on the left is resistant and
the two on the right are susceptible (courtesy of Dorrance et al., 2007).
