The distribution pattern of two juvenile hormone related compounds in Fraser fir and the induced response to a balsam woolly adelgid infestation

Abstract

Two juvenile hormone related compounds (JRCs), juvabione and dehydrojuvabione, were isolated from Fra- ser fir, Abies fraseri (Pursh) Poirit. Both juvabione and dehydrojuvabione concentrations had large variations across the tested trees and within trees. Juvabione, but not dehydrojuvabione, was much higher in stemwood then in branchwood. There was no significant difference in either chemical in relation to high, low, or middle branch position. To determine if juvabione concentration was influenced by an infestation of balsam woolly adelgid, Adelges piceae Ratz., branches from infested and uninfested 11-year-old Abies fraseri with were sampled at the bottom, middle, and top branches of each tree. While mean juvabione concentrations for each infested fir were higher than their uninfested counterparts, only the infested middle tree sections had mean juvabione values that were substantially higher ( p = 0.078) than the corresponding uninfested tree section of all the infested firs. The two infested Abies fraseri that maintained apical dom- inance demonstrated the highest upper branch levels of juvabione of all the infested. These results indicate that juvabione may be induced in small Abies fraseri in response to adelgid attack. Trees that produce large quantities of this compound may possess tolerance to the adelgid. Further research is needed to elucidate this possibility. Resume : Deux composes analogues a l'hormone juvenile, la juvabione et la dehydrojuvabione, ont ete isoles chez le sapin de Fraser, Abies fraseri (Pursh) Poirit. Les concentrations de ces deux composes presentaient de fortes variations intra et inter-arbres. Contrairement a celle de la dehydrojuvabione, la concentration en juvabione etait beaucoup plus elevee dans le bois des tiges que dans celui des branches. Aucun des deux composes ne montrait de difference signifi- cative en relation avec la position inferieure, mediane ou superieure des branches dans la cime. Pour determiner si la concentration en juvabione etait influencee par une infestation de pucerons lanigeres du sapin, Adelges piceae Ratz., des branches ont ete prelevees dans les sections inferieure, mediane et superieure de la cime d' Abies fraseri âges de 11 ans, infestes et non infestes. Alors que les concentrations moyennes en juvabione de chacun des sapins infestes etaient plus elevees que celles de leurs homologues non infestes, seules les sections medianes infestees exhibaient des valeurs moyennes de juvabione substantiellement superieures (p = 0,078) a celles des sections correspondantes, non infestees, de tous les sapins infestes. Parmi tous les arbres infestes, les deux Abies fraseri qui avaient conserve une dominance apicale presentaient les niveaux les plus eleves de juvabione dans leurs branches superieures. Ces resultats indiquent que la juvabione pourrait etre induite par une attaque de pucerons chez les jeunes Abies fraseri. Les arbres produisant ce compose en grande quantite pourraient etre tolerants aux pucerons. La verification de cette hypothese necessite da - vantage de travaux de recherche. (Traduit par la Redaction) Fowler et al. 1707