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Hemlock - Blueberry Rust
Naohidemyces vaccinii (Wint.) Sato, Katsuya et Hiratsuka
(=Pucciniastrum vaccinii (Wint.) Joerst.)
(=Pucciniastrum myrtilli Arthur)
Basidiomycotina, Uredinales, Pucciniastraceae
Hosts: In B.C., the aecial hosts of Naohidemyces vaccinii are western, mountain, and eastern hemlock. The telial hosts in B.C. include black huckleberry, dwarf bilberry, grouseberry, evergreen huckleberry, he-huckleberry, lignonberry, little-leaf huckleberry, oval-leaf blueberry, red huckleberry, and velvet-leaf blueberry.
Distribution: This fungus is widely distributed throughout the range of its hosts in B.C.
Identification: The infected needles of hemlock become chlorotic or discoloured and may be shed prematurely (Figs. 37a, 37b, 37c). Diseased trees therefore show symptoms of needle necrosis and thinning foliage. Yellow-orange aeciospores are produced in shallow-conical aecial pustules that develop in rows on the lower surface of needles (Fig. 37d).
Uredinia are produced on the lower surface of leaves on the alternate host, appearing as pustules which produce yellow-orange urediniospores (Fig. 37e). In late summer, telia form as flat, dark-coloured crusts on lower leaf surfaces.
Microscopic Characteristics: Spermogonia hypophyllous, subcuticular, without bounding structure, 80-150 µm in diameter and up to 70 µm in height. Aecia on current years needles rarely on cone scales, hypophyllous, in two rows divided by midrib of needle, 200-400 µm in diameter, 100-200 µm in height, subepidermal in origin, dome-like, peridium with many hemi-spherical differentiated ostiolar cells 10-14 µm in diameter. Aeciospores globose to sub-globose, often narrower at the bottom, conspicuously echinulate (Fig. 37f), borne singly on pedicels, 19.5-29 x 14-19.5 µm, yellow. Uredinia hypophyllous, up to 500 µm in diameter or sometimes several coalescing, dome-shaped, peridium with conspicuous ostiolar cells (14)16.5-43 x 7.5-17.5 µm. Urediniospores subglobose, echinulate, 17.5-27.5 x 10-19 µm (Fig. 37g). Teliospores one spore deep, consisting of several laterally adherent cells within epidermal cells, 20-30 x 18-23 µm in surface view, 16-22 mm in height, one germ pore in the centre of each cell, wall lightly pigmented.
Damage: Damage to either host is negligible and localized in areas where hemlock regeneration grows intermingled with huckleberries and blueberries.
Remarks: Until recently, this rust was considered a part of the genus Pucciniastrum. However, because of the unique structure of its aecia, it has been placed in the genus Naohidemyces. Another needle rust, Melampsora epitea, which is also found on hemlock could be confused with N. vaccinii. The aecia of M. epitea are "loose," with no peridium covering the aeciospores, while those of N. vaccinii have a dome-shaped covering with a centrally located hole (ostiole) through which spores are released.
References:
Sato, S., K. Katsuya, and Y. Hiratsuka. 1993. Morphology, taxonomy and nomenclature of Tsuga-Ericaceae rusts. Trans. Mycol. Soc. Japan 34: 47-62.
Ziller, W. G. 1974. The tree rusts of western Canada. Can. For. Serv., Publ. No. 1329. Victoria, B.C.
Figures
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Figure 37a: Discoloured hemlock needles resulting from Naohidemyces vaccinii infection.
Figure 37b: Discoloured hemlock needles resulting from Naohidemyces vaccinii infection (upper needle sufaces).
Figure 37c: Discoloured hemlock needles resulting from Naohidemyces vaccinii infection (lower needle surfaces).
Figure 37d: Aecia on the lower surface of hemlock needles.
Figure 37e: Uredinia on Vaccinium.
Figure 37f: Echinulate aeciospores of N. vaccinii and dome-shaped aecium.