Shoot Blight of Lodgepole Pine Seedlings in Nebraska Caused by Sphaeropsis sapinea

Shoot blight was observed on lodgepole pine (Pinus contorta Douglas ex Loud.) seedlings in fall 1994 at the USDA Forest Service Bessey Tree Nursery, Halsey, NE. Shoots were stunted, cankered, and sometimes curled at the tips, and bore brown needles that often had been killed before full elongation. Pycnidia were present on necrotic needles and stems. Conidia from these pycnidia produced pure cultures of Sphaeropsis sapinea (Fr.:Fr.) Dyko & Sutton in Sutton. The fungus was identified based on cultural, pycnidial, and conidial characteristics and comparison with known isolates. Also, random amplified polymorphic DNA markers of isolates were consistent with those of the A morphotype of S. sapinea (1). The ability of each of the two recognized morphotypes of S. sapinea to cause shoot blight of lodgepole pine was tested by inoculation of potted, 2-year-old seedlings in a greenhouse. Elongating terminal shoots were wounded by removing a needle pair approximately 1 cm below the shoot apex. A plug cut from an actively growing culture on water agar (WA) was placed fungus-side-down on the wound. The two isolates used (128, A morphotype; and 124, B morphotype) are representative of larger collections of these two morphotypes for which aggressiveness has been compared (2). Noncolonized WA plugs were placed on similarly wounded control seedlings. Nonwounded control seedlings also were used. Parafilm was wrapped around the shoots to hold the agar plugs in place and was removed 1 week later. Each treatment was applied to 10 seedlings in each of five completely randomized replicates. After 4 weeks, the condition (living or dead) of shoot tips was recorded, and the length of necrotic stem (canker) below the point of inoculation was measured to the nearest 0.25 cm. Segments of shoots were harvested, surface sterilized, and incubated to determine the presence of the pathogen. Analyses of variance were performed with Minitab for Windows version 10.1 software (Minitab Inc., State College, PA). Seedlings inoculated with either morphotype developed symptoms resembling those observed in the nursery. Neither incidence of shoot tip death nor severity (as indicated by canker length) differed greatly according to isolate morphotype. The means for number of shoot tips killed by the A and B isolates were 8.8 and 6.4 (out of 10), respectively (P = 0.07). The means for lengths of cankers produced by the A and B isolates were 4.9 and 3.8 cm, respectively (P = 0.10). Among controls, only one wounded seedling developed any symptoms. The pathogen was identified on incubated shoot segments from inoculated seedlings, but not those of control seedlings. This is the first report of S. sapinea as a cause of shoot blight of lodgepole pine in the U.S., and it associates the A morphotype with damage observed in the Bessey nursery. Further, the ability of the B morphotype to cause disease of lodgepole pine is established. Results of inoculations contrast with those obtained with red pine (Pinus resinosa Aiton) seedlings, on which the B morphotype was not aggressive (2). Susceptibility of lodgepole pine seedlings to both A and B morphotypes of S. sapinea, however, is similar to that exhibited by the related species, jack pine (P. banksiana Lamb.) (2). These species are classified in subsection "contortae" of the genus Pinus. Both morphotypes of S. sapinea should be considered as potential causes of shoot blight encountered on lodgepole pine. References: (1) G. R. Stanosz et al. Plant Dis. 80:1175, 1996. (2) J. T. Blodgett and G. R. Stanosz. Plant Dis. 81:143, 1997.