Lanterna Rally

Author: Cynthia L. Broberg

Publisher:

Published: 2005

Total Pages: 0

ISBN-13:

Hybrid poplar clones show varying levels of attack by Cryptorhy17chus lapathi (L.), a wood-boring weevil. I investigated olfaction, feeding, oviposition and larval survival as well as phenological and biochemical differences among four hybrid poplar clones in order to determine the underlying mechanisms of resistance. Weevils did not discriminate between resistant and susceptible clones based on olfaction in pitfall bioassays or antenna1 responses, but did discriminate against the most resistant hybrid, NM 6 (Populus nigra L. x Populus maxinzowiczii Henry), in choice and no-choice pairedtwig feeding bioassays. In addition, the most susceptible hybrid, TN 302-9 (Populus trichocarpa Torrey and Gray x P. nigra), was preferred for feeding over Salix scouleriana Barratt e.x Hooker, a preferred host in the wild. However. these feeding preferences were not consistently held, therefore resistance can only be partially based on antixenotic cues prior to oviposition. In choice and no-choice experiments involving potted or field-planted clones, oviposition occurred somewhat less frequently and abundantly on two clones with P. maximouiczii parentage. However, no larvae survived on field-planted NM 6 and only four emerged from TM 256-28 (P. tiichocarpa x P. ma.ximot̃iczii). In contrast, 50 and 140 adults emerged from the two susceptible clones, TD 52-226 (P. trichocarpa x Populus deltoides Bartram ex Marshall) and TN 302-9, respectively. Thus, resistance partially involves decreased levels of oviposition, but more significantly, antibiosis in resistant clones prevents the developnẽnt of larvae, probably in early spring. The two resistant hybrids flushed earlier, but no differences were found with respect to sap flow or bark moisture content that could explain larval mortality. Similarly, constitutive levels of nutritive compounds (sitosterol, nitrogen, linoleic and linolenic acids, and carbohydrates) were generally lower, or not significantly different, in TN 302-9. Thus, all hybrids appear nutritionally sound. TN 302-9 contained high constitutive levels of condensed tannins and catechin, but overall phenolic glycoside levels (salicin and salicortin) were similar anlong all hybrids, with the exception of one sampling date. Neither induced or constitutive polyphenol oxidase (PPO) activity nor induced levels of secondary metabolites could explain resistance. Thus, the resistant hybrids with P. rnaxirnolticzii parentage have a novel mechanism for resistance.