Quantification of Conidia of Diplodia spp. Extracted from Red and Jack Pine Cones

Frequency of detection and inoculum production by the conifer shoot blight and canker pathogens Diplodia pinea and D. scrobiculata on cones of red pine (Pinus resinosa) and jack pine (P. banksiana) were studied. Cones were collected from the ground and from canopies of red and jack pine trees in mixed stands at three sites in each of two different locations during two consecutive summers in Wisconsin. Conidia were extracted in water, quantified, germination tested, and the Diplodia species present was determined using molecular methods. At least one pathogen was detected from each tree at each site in both years. Overall, more conidia were extracted from cones from canopies than cones from the ground and from red pine cones than jack pine cones. Both total numbers of conidia extracted and proportions of cones yielding D. pinea or D. scrobiculata varied by location and pine species. Cones from either the ground or canopies can be used for surveys to detect Diplodia spp. at a given site but cones from canopies may be more useful to determine the relative abundance of potentially available inoculum of these pathogens.