INHIBITION OF ETHYLENE BIOSYNTHESIS AND THE ENDOGENOUS ETHYLENE AND CHLOROPHYLL CONTENT OF POA-PRATENSIS LEAVES INFECTED BY BIPOLARIS-SOROKINIANA

The ethylene-biosynthesis-inhibiting substances CAN, AOA, AIB, CCCP, C OCL, and PG were applied to roots of intact Poa pratensis to determine their ability to decrease endogenous ethylene production and subseque nt chlorophyll (Chl) loss from leaves inoculated with Bipolaris soroki niana. Endogenous ethylene of leaf blades was measured 24, 48, 72, and 96 h after inoculation, as pathogenesis progressed, and Chl content w as determined at 96 h. Endogenous ethylene was significantly decreased at each 24-h sampling period by CAN, AOA, CCCP, and PG. Loss of Chl d uring pathogenesis was substantially decreased by CAN and AOA, but Chl loss in response to CCCP and PG did not differ from that of the untre ated, inoculated control (43 % of control). The differential response of Chl loss to the ethylene inhibitors suggests that substances blocki ng the conversion of AdoMet to ACC are more effective at decreasing th e endogenous ethylene surge and preventing Chl loss during pathogenesi s than are substances that block the conversion of ACC to ethylene. Th e ethylene and Chl responses are discussed relative to physiological m anipulation of symptom expression.