Pierluigi Bonello

Systemic effects of Heterobasidion annosum on ferulic acid glucoside and lignin of presymptomatic ponderosa pine phloem, and potential effects on bark-beetle-associated fungi.

Concentrations of soluble phenolics and lignin in the phloem of ponderosa pines inoculated with the pathogen Heterobasidion annosum were assessed over a period of 2 years in a 35-year-old plantation in northern California, USA. The major effect of the pathogen on phloem-soluble phenolics consisted of a significant accumulation of ferulicacid glucoside: 503 ± 27 μg/g fresh weight (FW), compared with 366 ± 26 μg/g FW for mock-treated and 386 ± 27 μg/g FW for control trees. Lignin content was negatively correlated with ferulic acid glucoside concentration, and there was an indication of lignin reduction in the cell walls of inoculated trees. Lignin had a negative effect on the in vitro growth of two common bark beetle fungal associates, Ceratocystiopsis brevicomi and Ophiostoma minus. For this reason it, is hypothesized that lower lignification may facilitate the growth of beetle-associated fungi, resulting in greater susceptibility of the presymptomatic host to bark beetle colonization.

The role of olfactory stimuli in the location of weakened hosts by twig-infesting Pityophthorus spp.

1. Senescing, shade‐suppressed, or broken branches of Monterey pine Pinus radiata are infested by twig beetles in the genus Pityophthorus (Coleoptera: Scolytidae). The studies reported here tested whether twig beetles can discriminate between healthy and pitch canker‐diseased branches, whether diseased branch tips produce more ethylene than undamaged controls, and whether ethylene and other volatiles, produced by the plant in response to tissue damage, are utilised by twig beetles in host location.

Feeding Response of Ips paraconfusus to Phloem and Phloem Metabolites of Heterobasidion annosum–Inoculated Ponderosa Pine, Pinus ponderosa

In studies of feeding by the bark beetle, Ips paraconfusus, two pine stilbenes (pinosylvin and pinosylvin methyl ether), ferulic acid glucoside, and enantiomers of the four most common sugars present in ponderosa pine phloem (sucrose, glucose, fructose, and raffinose) did not stimulate or reduce male feeding when assayed on wet α-cellulose with or without stimulatory phloem extractives present. When allowed to feed on wet α-cellulose containing sequential extracts (hexane, methanol, and water) of ponderosa pine phloem, methanol and water extractives stimulated feeding, but hexane extractives did not. Males confined in wet α-cellulose containing aqueous or organic extracts of culture broths derived from phloem tissue and containing the root pathogen, Heterobasidion annosum, ingested less substrate than beetles confined to control preparations. In an assay using logs from uninoculated ponderosa pines, the mean lengths of phloem in the digestive tracts increased as time spent feeding increased. Males confined to the phloem of basal logs cut from ponderosa pines artificially inoculated with H. annosum ingested significantly less phloem than beetles in logs cut from trees that were (combined) mock-inoculated or uninoculated and did not contain the pathogen. However, individual pathogen-containing treatments were not significantly different from uninoculated controls. It was concluded that altered feeding rates are not a major factor which may explain why diseased ponderosa pines are colonized by I. paraconfusus.