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Studies were made on the root-surface fungi of soybean grown in field plots where various soil temperature and moisture environments had been maintained for five previous growing seasons. Washed-root segments were incubated on agar plates at temperatures corresponding to those of the field plots. Fusarium was the most abundant genus appearing on the plates. Species of Mucor, Trichoderma, Alternaria, Mortierella, Aspergillus, Corynespora, Rhizoctonia, Penicillium, Gliocladium, and sterile forms appeared fairly frequently. Statistical analysis of the data revealed that changes in soil and incubation temperature markedly affected the relative frequency of 12 genera, and age of plant significantly affected nine genera. Soil moisture influenced the frequency of only one genus. High soil and incubation temperature (28 C) encouraged greater root populations of Rhizoctonia early in the season, Trichoderma and Aspergillus throughout the growing season, and Fusarium late in the season. Low soil temperature conditions (12 C) favored growth of Pythium, Mortierella, Mucor, Alternaria, Cladosporium, throughout the growing season, and Corynespora and Cylindrocarpon, primarily during mid-season. Late in the season Gliocladium preferred the intermediate temperature of 20 C.

A total of 20 species of fungi representing 12 genera were found to be associated with Datura metel L. in Bangladesh. The fungi were Alternaria alternata (Fr.) Keissler, Arthrinium saccharicola Stevenson, Aspergillus niger Van Tiegh., A. flavu s Link ex Fr,, Cladosporium elatum (Harz) Nannf . , C. coffeanum Noack, C. gloeosporioides {Penz.) Sacc., C. graminicola (Ces.) Wilson, Corynespora pruni (Berk. & Curt.) M. B. Ellis, Curvularia fallax Boedijn , C. lunata (Wakker) Boedijn , C. penniseti ( Mitra) Boedijn , C. prasadii R.L. & B.L Mathur, Fusarium flocciferum Corda. Sturm's Deutschl, F. nivale (Fr.) Ces., Rabenth. Herb., Nigrospora sphaerica (Sacc.) Mason, Penicillium spp . , Pseudocercospora fuligena (Roldan) Deighton, Rhizopus stolonifer (Ehrenb. ex. Fr.) Lind and one sterile unidentified fungal species . The percentage of association of Cladosporium elatum isolated from infected fruits was higher than any other fungi. Arthrinium saccharicola , Colletotrichum coffeanum, Corynespora pruni, Fusarium flocciferum and F. nivale are new records for Bangladesh. Key words: Fungi; Association; Datura metel DOI: http://dx.doi.org/10.3329/dujbs.v19i1.8947 DUJBS 2010; 19(1): 83-89

A disease of Hibiscus syriacus interested the author, since the causal fungus has been thought to belong to a rarely known, but an important fungal genus. The disease spots appear on the leaves first in summer, but it becomes severe in autumn. The spots are subcircular, at first light brown, discolor to dark brown, then greyish brown. It is caused by a fungus Corynespora Hibisci nov. spec. Since the genus Corynespora was established by GUSSOW in 1906, it has long included one species only. In some cases even the existence of the genus was doubted. C. Hibisci, the causal fungus of the brown spot disease, is the second species in this genus. Isolation and inoculation of the causal fugnus has been carried out and the pathogenic nature of this fungus has been ascertained. Germ-tubes are sent from the distal or proximal end of the conidia. At the tip of the germ-tubes an appressorium is formed, and an infection hypha is sent, which penetrates the epidermis at the anticlinal wall of the epidermal cells. Soon a necrosis occurs in the host tissues. A detailed comparison of the causal fungus with related fungi and its technical description have been given.

Summary Azotobacter cultures which were studied for their fungistatic action towards different plant pathogenic fungi in iquid medium were used to assess their effect on spore germination of Alternaria (5 cultures), Curvularia (5 cultures) Corynespora (1 culture), Fusarium (3 cultures) and Helminthosporium (4 cultures). The germination percentage was recorded at the end of 6 hours at 30 °C.

Molecular phylogenetic analyses of a multigene matrix of partial nuSSU-ITS-LSU rDNA, rpb2 and tef1 sequences were performed to investigate the phylogenetic relationships of Corynespora, Exosporium and Helminthosporium species. Based on phylogenetic analyses and morphology, the genus Exosporium is synonymised with Helminthosporium, and the genus Corynespora is revealed as polyphyletic. Corynespora smithii is confirmed to be closely related to the generic type C. cassiicola and its morphology is described and illustrated. Exosporium tiliae, Corynespora caespitosa, C. endiandrae, C. leucadendri and C. olivacea are recognised in Helminthosporium, and Splanchnonema quercicola and S. kalakadense are combined in Helminthosporium. Based on pure culture studies and DNA sequence data, Massaria heterospora and Massarinula italica are shown to be the sexual morphs of Helminthosporium tiliae and H. microsorum, respectively. European accessions of Splanchnonema quercicola are recognised to differ from the North American type and are described as Helminthosporium quercinum. The sexual morph of H. oligosporum is recorded and described for the first time. The generic type of Helminthosporium, H. velutinum, is epitypified with a recent collection from the type host, Fagus sylvatica. Based on sequence data, Helminthosporium genistae is recognised as a distinct species. Several species for which subperidermal stromata have been reported are shown to be fungicolous on Diaporthales, the “stromata” representing aborted and transformed host stromata or conidiomata: H. caespitosum, H. microsorum, H. quercicola and H. quercinum on Coryneum spp.; H. hispanicum on conidiomata of Juglanconis juglandina; H. juglandinum on conidiomata of Diaporthe sp.; H. oligosporum and H. tiliae on Hercospora tiliae. The newly described H. austriacum is fungicolous on Amphisphaeria cf. millepunctata (Xylariales).

Four dematiaceous hyphomycetes associated with grey colonies on stems and branches and 1 species associated with necrotic phyllode lesions of Acacia spp. are described and illustrated. Corynespora alternarioides on stems of A. mitchellii differs from previously described species in having muriform obpyriform conidia and non-proliferating conidiogenous cells. Corynespora queenslandica is associated with distinct lesions on phyllodes of A. leiocalyx, A. concurrens and A. aulacocarpa and again has non-proliferating conidiogenous cells but long filiform conidia. Sporidesmium corrugatescens on stems of A. dealbata combines micronematous conidiophores and distoseptate verrucose conidia. Janetia refugia on stems of A. elata has finely verruculose distoseptate conidia, the basal cell of which is darker and protuberant, and short conidiogenous cells which are more deeply pigmented towards the apices, while J. canescens on stems of A. fimbriata and A. linifolia has polyblastic conidiogenous cells and pyriform to cylindrical conidia in which the base is more darkly pigmented and the walls are distinctly invaginated at the distosepta.