Comparison of various stress responses in oat in compatible and nonhost resistant interactions with rust fungi

The role of extracellular beta-1,3-glucanases and chitinases was investigated in oat leaves after infection with different rust fungi. The oat leaves (Avena sativa L .) were inoculated with the compatible rust Puccinia coronata f. sp . avenae and the two nonpathogens Puccinia recondita f. sp. tritici and Puccinia graminis f. sp. tritici. No alterations in enzyme activities were found in the compatible interaction . In the nonhost interaction with P. recondita ff sp. tritici beta-1,3-glucanase and chitinase activities increased by 100 % 24 h after infection. With P. graminis f. sp . tritici the activities of both enzymes increased about twofold after 48 h. In both nonhost interactions the observed increase in activity was due to the induction of an acidic fl-1,3-glucanase and a chitinase whereas the activity of the basic enzymes did not change. This increase is small compared to other systems and apparently the enzymes are not able to inhibit growth of the different rust fungi. Treatment of noninfected plants with the abiotic stress factor mercuric chloride induced necrosis and production of avenalumins but had no effect on the activities of the two enzymes investigated. In the nonhost systems no alteration of peroxidase activity and no induction of avenalumins could be found. Our results indicate that mechanisms other than the stress responses of oat plants studied so far are active in nonhost resistance