INDUCTION OF PHENYLALANINE AMMONIA-LYASE ACTIVITY AND CONTROL OF SPHAEROPSIS-SAPINEA INFECTION IN PINUS-RADIATA BY 5-CHLOROSALICYLIC ACID

Phenylalanine ammonia lyase (PAL) activity increased rapidly in Pinus radiata seedlings after treatment with 2 mM 5-chlorosalicylic acid (5C SA) and peaked after 48 h at four-times the level of the control. Elev ation of PAL is often associated with the induction of host resistance mechanisms. Thus, effects of 5CSA on subsequent infection of P. radia ta by Sphaeropsis sapinea Nas investigated. Only one out of 16 seedlin gs treated with 2 mh? 5CSA, 4 days before inoculation, developed deadt op compared to 14 of the controls. The 5CSA was directly inhibitory at this concentration and reduced growth rate of S. sapinea on agar by 2 7%. However, antifungal activity does not fully account for the observ ed disease control afforded by 5CSA since 0.5 mM and 0.25 mM 5CSA, whi ch did not inhibit growth of S. sapinea, significantly reduced the inc idence of deadtop Furthermore, 1 mh? 5CSA protected seedlings against fresh inoculation challenge for up to 32 days after application. Such durable resistance is unlikely to be attributable to the direct effect s of the applied compound and may suggest the involvement of inducible host resistance mechanisms.