September, 1999

Differences in Aggressiveness of Sphaeropsis sapinea RAPD Marker Group Isolates on Several Conifers. J. T. Blodgett, former Postdoctoral Research Associate, and G. R. Stanosz, Associate Professor, Departments of Plant Pathology, and Forest Ecology and Management, University of Wisconsin-Madison, 1630 Linden Drive, Madison 53706-1598. Plant Dis. D-1999-0709-01R, 1999 (on-line). Accepted for publication 3 June 1999.

Sphaeropsis shoot blight and canker disease caused by the fungus Sphaeropsis sapinea can result in extensive losses of native and exotic conifers throughout the world. Damage can occur in nurseries, Christmas tree and ornamental plantings, and forest stands affecting hosts in at least eight coniferous genera. Two types of this pathogen (groups A and B) were originally differentiated by their appearance in culture. However, these groups can be differentiated more clearly using a molecular technique called random amplified polymorphic DNA (RAPD). The relative susceptibility of the hosts of this pathogen cannot be determined from the literature because of a lack of comparative trials under controlled conditions and the use of unknown pathogen groups. This study compared the aggressiveness of both groups of this pathogen on seedlings of Scots pine varieties East Anglia and Austrian Hills, red pine, mugho pine variety Pumileo, Colorado blue spruce, Douglas-fir, and balsam fir. Although group A isolates were more aggressive on most of the hosts, group B isolates caused measurable symptoms on blue spruce. Hosts varied considerably in their responses to group A isolates, with East Anglia Scots pine being the most susceptible and balsam fir the least susceptible. Both fungal groups also survived in or on healthy-appearing trees. The findings emphasize the importance of distinguishing the group(s) of this pathogen encountered in the field or used in research; the need to compare resistance among coniferous genera, species, and varieties to both groups of this pathogen; and the potential for both groups of the pathogen to survive in or on healthy-appearing trees. Planting species or varieties resistant to this pathogen would be desirable where it is known to cause loss. Our methods can be used to quantify differences in resistance to each pathogen group among a variety of coniferous hosts and to select resistant host material.