© 2004 Plant Management Network.
First Report of Leptographium abietinum Associated with Blue Stain on Declining Western Siberian Larch in Alaska
Jenifer H. McBeath, M. Cheng, P. Gay, and M. Ma, Plant Pathology and Biotechnology, Agriculture and Forestry Experiment Station, University of Alaska Fairbanks, Fairbanks 99775-7200; and John Alden, Alaska Division of Forestry, Department of Natural Resources, Fairbanks 99707-4699
Corresponding author: Jenifer H. McBeath. email@example.com
McBeath, J. H., Cheng, M., Gay, P., Ma, M., and Alden, J. 2004. First report of Leptographium abietinum associated with blue stain on declining western Siberian larch in Alaska. Online. Plant Health Progress doi:10.1094/PHP-2004-0326-01-HN.
Western Siberian larch (Larix sukaczewii N. Dyl.), a fast-growing tree species, was introduced to Alaska in 1949 to evaluate its commercial potential. Early plantings demonstrated that L. sukaczewii adapted well to subarctic climatic conditions; L. sukaczewii is currently the fastest growing conifer in areas of Alaska outside of the southeastern region. During 2002, dead tops, branch dieback, and resinosis were observed in 20-year-old L. sukaczewii stands in Interior Alaska. In 1995, these plantations were heavily infested with larch sawfly (Pristiphora erichsonii (Hartig)). Examination of dead and dying trees revealed the presence of blue stain in the sapwood and galleries of eastern larch beetles (Dendroctonus simplex (LeConte)) under the bark (R. A. Werner, personal communication).
Surface-sterilized tissues from the margin of the blue stain were plated on 2% malt extract agar. A Leptographium species was consistently recovered (Fig. 1). It produced brown conidiophores that were erect, macronematous, mononematous with a mean length of 213 µm (range 75.4 to 592.8 µm), and lacked rhizoid-like structures. The stipe was brown, smooth, and cylindrical, with 0 to 13 septa and a mean length of 147.7 µm (range 18.2 to 488.8 µm) and diameter of 5.1 µm (range 2.6 to 7.8 µm). Basal cells were swollen, but apical cells were not. The conidiogenous apparatus, with a mean length of 65.2µm (range 33.8 to 104 µm), excluding the conidial mass, had 2 to 4 series of cylindrical branches: 2 to 3 primary branches, were light brown to brown, smooth, cylindrical, aseptate, 11.5 µm long (range 5.2 to 23.4 µm) and 4.8 µm wide (range 2.6 to 6.5 µm); secondary branches were hyaline to light brown, aseptate, 8.7 µm long (range 5.2 to 15.6µm) and 2.4 µm wide (range 1.3 to 3.9 µm); tertiary branches were hyaline, aseptate, 9.7 µm long (range 5.2 to 18.2 µm) and 2.4 µm wide (range 1.3 to 3.9 µm); and quaternary branches were hyaline, aseptate, 8.2 µm long (range 6.5 of 10.4 µm) and 2.1 µm wide (range 1.8 to 2.6 µm). Conidiogenous cells were discrete, 2 per branch, tapered slightly at the apex, and were 31.5 µm long (range 15.6 to 57.2 µm) and 1.4 µm wide (range 0.8 to 2.6 µm). Conidia were hyaline, aseptate, curved slightly at the base with a mean length and width of 7.0 × 2.0 and a range of 1.8 to 13 × 1.3 to 2.8 µm. Conidia accumulated in slimy droplets at the apices of the conidiogenous apparatus. Morphological characteristics were thus indicative of Leptographium abietinum (1). For molecular verification of this classification, primers corresponding to the 28S ribosomal gene for Leptographium species (forward primer [ITS3]: 5’-GCATAGATGAAGAAGCAGC-3’; reverse primer [LR3]: 5’-CCGTGTTTCAAGACGGG-3’) (2) and genomic DNA isolated from the purified fungal culture as the template were used in a polymerase chain reaction. An approximately 430-nucleotide product was recovered and sequenced from three replications [GenBank Acc. No. AY380784] (Fig. 2). A GenBank search revealed a direct match (100% identity) between our isolate and L. abietinum [GenBank Acc. No. AF343669] (2). L. abietinum has been found to cause blue stain on Lutz, Sitka, and white spruce in Alaska (3, 4).
Leptographium abietinum has not been identified on western Siberian larch elsewhere in the world; although other Leptographium anamorphs have been identified on larch (Larix laricina) in Japan (5). This is the first report, to our knowledge, of blue stain caused by Leptographium in western Siberian larch in Alaska. No other Leptographium species have been found on western Siberian larch in Alaska. Association of eastern larch beetles with L. abietinum remains to be elucidated.
1. Jacobs, K. and Wingfield, M. J. 2001. Leptographium Species. American Phytopathological Society, St. Paul, MN.
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3. Reynolds, K. M. 1992. Relations between activity of Dendroctonus rufipennis Kirby on Lutz spruce and blue stain associated with Leptographium abietinum (Peck) Wingfield. For. Ecol. Man. 47:71-86.
4. Werner, R. A., and Illman, B. L. 1994. Response of Lutz, Sitka, and white spruce to attack by Dendroctonus rufipennis (Coleoptera: Scolytidae) and blue stain fungi. Environ. Entomol. 23:472-478.
5. van der Westhuizen, K., Wingfield, M. J., Yamaoka, Y., Kemp, G. H. J., and Crous, P. W. 1995. A new species of Ophiostoma with a Leptographium anamorph from larch in Japan. Mycol. Res. 99:1334-1338.