In susceptible varieties, the hypodermic is narrow and lignin concentration is low. It is believed that these two factors are responsible for resistance. The fungus is not able to decompose the lignin and penetration of the wide hypodermic layer is greatly reduced. Unfortunately the measurement of these two characteristics is very time consuming and expensive. Murray's more recent laboratory work with seedlings has revealed another possible means of evaluating resistance.
Resistant varieties react differently to infection than susceptible varieties.
Resistant varieties were found to have increased lignin concentration at the site of infection which blocked further movement of the fungus into the leaf sheath. Typically, resistant varieties had about 2 percent infection rates compared to 80 percent infection rates for susceptible varieties. To date, six varieties have been tested extensively and results correlate closely with reaction in the field. If the seedling test continues to prove reliable, it offers the potential to greatly accelerate the screening of large numbers of varieties and experimental lines in a very short period of time. Studies are also underway to evaluate the genetic heritability of the resistance reactions evaluated in the seedling tests.