Manipulation of the temperature-sensitive interaction between soybean leaves and Pseudomonas syringae pv. glycinea—implications on the nature of determinative events modulating hypersensitive resistance

Abstract

The interaction between race 1 of Pseudomonas syringae pv. glycinea and cv. Harosoy soybean leaves was temperature sensitive for reaction-type—an incompatible reaction involving hypersensitive host cell death and glyceollin accumulation occurred at 22 °C but a compatible reaction resulted when inoculated plants were incubated at 31 °C However, fully resistant reactions occurred at 31 °C if inoculated plants were previously incubated at 22 °C for 18 h. This and other evidence indicated that the higher temperature did not inhibit resistance expression per se but affected an earlier event, probably the determinative phase specific to this race-cultivar interaction. Intermediate levels of resistance resulted when plants were shifted to 31 °C at 8 or 12 h after inoculation but resistance was not expressed when plants were shifted at 4 h; therefore, the determinative events leading to resistance expression had begun by c . 8 h and were complete by c . 18 h after inoculation. In contrast, resistance was always expressed when inoculated plants were incubated at 31 °C for various time periods and then shifted to 22 °C, even after 96 h when bacterial populations had reached maximum levels. Thus, it was concluded that compatibility was not specified through mechanisms involving induced host susceptibility or suppression of resistance. Instead, the observations confirm other evidence indicating that incompatibility is the specifically determined plant response and that compatibility results from the failure of incompatible recognition to occur. Finally, the results support the role of glyceollin in conferring resistance of soybean leaves to P. syringae pv. glycinea .