First Report of Dothistroma septospora on Native Limber and Whitebark Pine in Montana.

Abstract

Dothistroma septospora (Doroguine) Morelet (= Dothistroma pini Hulbary), the anamorph of Mycosphaerella pini Rostr. in Munk, has been reported to cause needle blight in 29 Pinus species and hybrids in North America, including limber pine (P. flexilis James) in plantings in Kansas, Nebraska, and Ohio. We are unaware of any reports of D. septospora on limber or whitebark pine (P. albicaulis Engelm.) growing within their native ranges in the western United States. In June 1997, limber and whitebark pine in Montana were observed with severe defoliation and symptoms typical of those caused by D. septospora: affected second- and third-year needles were green at the base with brown tips or reddish-brown spots or bands, and black fruiting bodies in discolored portions of needles. Symptomatic needles were collected in natural stands of limber pine at 22 locations representing 15 counties in central, south-central, and southwestern Montana, and whitebark pine at three locations representing two counties in the Crazy Mountains in south-central Montana. Approximately 20 needles and five stromata from each location were examined with dissecting and compound microscopes to observe morphological features. Stromata were black, linear, 150 to 1450 μm (average 650 μm) by 65 to 450 μm (average 190 μm), subepidermal, and erumpent. Conidiophores were hyaline and unbranched. Conidia were 16.0 to 23.5 μm (average 18.5 μm) by 3.0 to 4.1 μm (average 3.4 μm), hyaline, 3 to 5 septate, blunt at the ends, and slightly falcate. The fungus described above was found at all sample locations. The teleomorph, M. pini, was not observed. Symptom expression and mycological characteristics were consistent with Hulbary's lectotype (1) of D. pini (= D. septospora). This is the first report of D. septospora on limber and whitebark pine within the hosts' native ranges. Reference: (1) R. L. Hulbary. Ill. Nat. Hist. Surv. Bull. 21:231, 1941.