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Phomopsis Canker of Douglas-fir

Diaporthe lokoyae Funk
(anamorph =Phomopsis lokoyae Hahn)

Ascomycotina, Diaporthales, Valsaceae

Hosts: In B.C., Diaporthe lokoyae has been reported on western larch, Sitka spruce, western redcedar, western hemlock, Douglas-fir, and dawn redwood.

Distribution: Phomopsis canker is widespread throughout the range of coastal Douglas-fir; most records of this disease are from the coastal regions, predominantly southern Vancouver Island and the lower mainland. One collection has been confirmed in the interior of the province, near Vernon.

Identification: Leader and branch dieback occurs associated with cankers on diseased seedlings and young trees. Cankers appear as brown, sunken, elliptical areas of dead bark with a well defined margin. They are often centered around a dead twig or branch, or are associated with dieback of growing shoots (Fig. 41). Fruiting bodies of both the sexual stage (Diaporthe), and the asexual stage (Phomopsis) form on the surface of the cankered bark as small (0.5 mm in diameter), dark-coloured pimples. Both types of fruiting bodies may be found throughout the year.

Microscopic Characteristics: Perithecia in clusters of 2-4, black, subglobose, 300-400 Ám diameter; ostioles cylindric, 100-270 Ám long. Asci cylindric, 8-spored, 36-68 x 7-12 Ám with apical refractive ring. Ascospores cylindric-ellipsoid, constricted at a single septum, terminal appendages at each end, hyaline, 10-16 x 2.5-4.5 Ám, each cell containing two oil drops. Paraphyses broad and tapering, up to 200 Ám long, 8-10 Ám wide at the base, 3-4 Ám wide at the rounded tip, hyaline, simple or branched, septate.

Pycnidia erumpent, black, lenticular to subglobose, 300-600 Ám in diameter, 200-300 Ám high. Conidiophores lining the single locule, flexuous, subulate, 5-20 Ám long; conidiogenous cells phialidic. Conidia of two types: a-spores hyaline, elliptic-fusoid, non-septate, containing two oil droplets, 6-10 x 2-4 Ám; ▀-spores hyaline, elongate-fusiform, nonseptate, minutely guttulate, 10-12 x 1.5-2.5 Ám.

Damage: Sporadic outbreaks of this disease occur in plantations and nurseries. Most damage is minor, particularly on older trees. Severe top-kill and girdling of younger trees can result in poor growth form or mortality.

Remarks: This disease is known as Phomopsis canker because the asexual stage is more common, and was described prior to the discovery of the sexual stage (Diaporthe).

References:

Funk, A. 1968. Diaporthe lokoyae n. sp., the perfect state of Phomopsis lokoyae. Can. J. Bot. 46: 601-603.


Figures

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Phomopsis canker on Douglas-fir - Click to see a larger version of this image

Figure 41a: Phomopsis canker on Douglas-fir.