BUTTERFLY STAIN OF CHILEAN TEPA IN BACTERIAL WETWOOD
-FH TAINTER, JB MCLEMORE and SD MCELREATH
Department of Forest Resources, Clemson University, Clemson, SC 29634-1003, USA
Background and objectives
Chilean tepa, Laureliopsis philippiana, is a valuable and plentiful temperate hardwood timber species. its importance in international markets is likely to increase in the next decade as demand for other hardwood species begins to exceed the supply. A request has been made to the Animal and Plant Health Inspection Service of the United States Department of Agriculture to permit importation of tepa logs into the US.
The only known major pathogen-related defect is a discoloration of the heartwood known as butterfly stain. This stain appears in the log cross-secton as a series of partially overlapping, orange-brown arcs, each limited by a black zone line, and is associated with a very strong, naphthalene-like odor. The stain and odor diminish the value of tepa logs and the products derived from them. The physical appearance and odor suggest a "wetwood" condition. While most wetwood research has focused on North Amedcan and European tree species, there has been little investigation of this condition in trees growing in other locales. This research characterized butterfly stain, identified aerobic and anaerobic bacteria associated with it, and determined effects of the stain on selected physical and mechanical properties of the wood.
Materials and methods
Cross-sectional disks (35 cm thick) were cut from the butts of 18 freshly felled tepa trees or logs in December 1995 from two locations in ValdMa province, Chile. Approximately half of the trees sampled had very small amounts or no visible butterfly stain and were designated as controls. These disk samples were used to characterize the stain and to determine and compare physical and mechanical properties of the stained versus nonstained wood. Subsamples were used for isolation of aerobic and facultatively anaerobic bacteria and for examination with scanning electron microscopy (SEM). The bacteria were identified using the Biolog Microbial Identification System, the Analytical Profile Index (API), and the MIDI or Microbial Identification System (MIS). In December 1996 increment core samples were aseptically collected from five stain-affected and two non-affected tepa trees in Puyehue National Park. The cores were placed in thioglycollate medium for transport to the United States. Obligately anaerobic bacteria were cultured, and idenfified by using the API 20A, RapiD ANA 11, and MIS systems.
Results and conclusions
Butterfly stain appears to be the result of a compartmentalizafion-like response to bacterial invasion associated with small branch death andlor bacterial invasion through the roots. Major aerobic or facultatively anaerobic bacteria associated with the stain were Pseudomonas, Erwinia, and a pectnolytic Bacillus. An isolate identified as Erwinia chrysanthemi produced a naphthalene-like odor similar to that of freshly cut stained wood. The major obligately anaerobic bactedal species isolated was Ciostridium. Wood samples from stain-affected trees, regardless of whether or not they contained stain, were weaker in compression and static bending than samples from nonaffected trees. SEM revealed degradation of pit membranes in stained wood. Nonstained wood had significantly less calcium and potassium than did stained wood and wood from the black zone line. The pH of the black zone line was 6.55, significantly greater than stained wood (5.17). Wood from stain-affected trees was significantly more hygroscopic than wood from nonstained trees, regardless of whether a particular sample contained stained wood. These results suggest that butterfly stain of tepa is similar to the wetwood phenomenon found in several North American timber species such as Uimus and Populus. They also suggest that the black zone line is the site of the majority of host andlor microbial activity in the process of wetwood formation in tepa.