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Abstract

Sapwood and crown symptoms in ponderosa pine infected with black-stain and annosum root disease.

Abstract

Crown growth parameters, extent of disease in roots, and volatile compounds from sapwood were measured for diseased and healthy ponderosa pine (Pinus ponderosa) in a relatively undisturbed stand dominated by the species in the Malheur National Forest, Oregon, USA. The pathogens were black-stain root disease caused by Leptographium wageneri var. ponderosum, annosum root disease caused by Heterobasidion annosum, or both. Samples of sapwood collected near the root collar were heated in sealed vials and volatile compounds analysed by gas chromatography. Acetaldehyde, acetone, ethanol, methanol, and 2-propanol (isopropyl alcohol) were quantified. Acetaldehyde was selected by logistic regression to be the best predictor for distinguishing healthy from diseased trees. Acetaldehyde concentrations were significantly lower in healthy trees. Concentrations of methanol and acetaldehyde from sapwood were positively correlated with the percentage of non-functional root area caused by disease, while length of the terminal leader and water content of sapwood from near the root collar were negatively related. Crown growth parameters did not change significantly until more than one-third of the root system was diseased. The mean ethanol concentration from diseased trees was significantly higher than that from healthy trees. About half of the diseased pine contained high ethanol concentrations, with substantial variation in concentrations among cardinal positions sampled around the root collar. While high ethanol concentrations were associated with diseased trees, low ethanol concentrations were not a good indicator of health. All volatiles, except ethanol, were partially or entirely generated by thermal decomposition of sapwood constituents when heated in sealed vials during analysis. Nevertheless, some of these may be useful chemical markers for identifying trees with root disease before the disease reaches an advanced stage; they might also be useful in estimating what proportion of a root system is diseased and non-functional.