Mycosphaerella suberosa Crous, F.A. Ferreira, Alfenas & M.J. Wingf. 1993
Details
Nomenclature
Classification
Associations
Descriptions
Mycosphaerella suberosa Crous, F.A. Ferreira, Alfenas & M.J. Wingf. 1993
Leaf spots epiphyllous, eventually becoming amphigenous, circular, 5-15 mm in diameter, becoming confluent, dark brown and corky with a diffuse yellow-red margin on the adaxial surface, abaxial surface discoloured and eventually becoming necrotic. Pseudothecia initially epiphyllous, eventually becoming amphigenous, numerous, discrete but densely scattered, black, globose, 60-70 µm wide, intraepidermal becoming erumpent, ostiole non-papillate, wall of variable thickness, thinnest at the base and thickest at the ostiole. Asci bitunicate, subsessile, 8-spored, ellipsoid to obclavate, straight or slightly curved, 30-40 x 1216 µm. Ascospores bi- to multi-seriate, guttulate, hyaline, smooth, obtuse at each apex, medianly 1septate, constricted at the septum, widest in the middle of the apical cell, tapering towards each apex but the taper more pronounced in the basal cell, 10-17 x 3-6 µm, with mucoid sheath. Anamorph not observed.
ASCOSPORE GERMINATION: Ascospores germinating after 48 h on water agar, becoming slightly piµmented and often with several germ tubes emanating from each of the two cells. Germ tubes form randomly and produce numerous septa. Ascospores become very distorted after forming 3-4 septa.
CULTURE: Colony diameter <5 mm after one month on 3% malt extract agar at 25°C in the dark, dull black, colony surface raised with a hard texture, aerial mycelium sparse. Margin entire, crenate and slightly appressed.
The pseudothecia are also slightly smaller, but the New Zealand collections generally agree with the previously published descriptions of M. suberosa (Table 1). The small differences in the morphological characters of the New Zealand fungus may be attributable to its presence on a host on which it has not previously been recorded. It is of interest to note that the hosts on which M. suberosa has been found in South America, Indonesia, and Australia (E. dunnii, E. globulus, E. grandis, E. moluccana, E. saligna, E. viminalis) belong to Eucalyptus subgenus Symphyomyrtus, whereas the New Zealand host, E. muelleriana, is in Eucalyptus subgenus Eucalyptus (Brooker 2000).
The New Zealand cultures of M. suberosa have been examined by A. W. Milgate (University of Tasmania) and the 5.8S and flanking ITS 1 and ITS2 regions of the rDNA sequenced for comparison with isolates of Australian Mycosphaerella species. The sequence from the New Zealand isolates of M. suberosa was identical with that from the Western Australian isolate of M. suberosa (VPRI 20605) described by Carnegie et al. (1997) (A. W. Milgate pers. comm.).