Phylogenetic Diversity of Rhizoctonia solani Associated with Canola and Wheat in Alberta, Manitoba, and Saskatchewan.

Rhizoctonia solani is a damaging soilborne pathogen, which affects most field crops in the Canadian provinces of Alberta, Manitoba, and Saskatchewan. The objective of this study was to conduct a phylogenetic comparison of isolates of R. solani collected from a previous survey in the major canola- and wheat-growing regions of western Canada. A total of 128 multinucleate isolates from a previous survey were identified by internal transcribed spacer (ITS) sequence and compared to anastomosis group (AG) results. The multinucleate isolates of R. solani were grouped into eight distinct clades. Each clade corresponded to a specific AG with the exception of two distinct clades that were observed for isolates classified as AG 2-1 by anastomosis testing. While most isolates of AG 5 clustered together according to ITS sequences, three isolates classified by anastomosis grouping as AG 5 grouped with AG 2-1, AG 4, and a binucleate Rhizoctonia sp. in the phylogenetic analysis. In most instances, the results from AG tests were consistent with ITS sequence, but there were still several cases where isolates were inconsistently classified or failed to undergo anastomosis with any of the tester strains used in this study. This provides support for the use of the ITS region as a valuable tool for rapid identification of R. solani isolates to their respective AGs.

A new 1-hydroxy-2,6-pyrazinedione associated with hypovirulent isolates of Sclerotinia minor.

A new 1-hydroxy-2,6-pyrazinedione, sclerominol (1), was isolated from cultures of hypovirulent isolates of Sclerotinia minor, a fungal plant pathogen associated with lettuce drop and other plant diseases. This compound was characterized by NMR, mass spectrometry, and X-ray crystallography. One other 1-hydroxy-2,6-pyrazinedione, flutimide, has been reported. Flutimide has activity as an inhibitor of influenza virus endonuclease, and therefore, sclerominol was evaluated for related biological activity. Sclerominol (1) displayed some activity against cancer cell lines but little activity against three influenza virus strains. The role of 1 in the physiology of hypovirulent isolates of S. minor has not been determined, but 1 has also been recovered from debilitated isolates of S. sclerotiorum.

Interspecific Transmission of Double-Stranded RNA and Hypovirulence from Sclerotinia sclerotiorum to S. minor.

ABSTRACT Interspecific transmission of a hypovirulence-associated double-stranded RNA (dsRNA) and hypovirulent phenotype was attempted from hypovirulent isolate Ss275 of Sclerotinia sclerotiorum to five virulent isolates of S. minor. dsRNA and the hypovirulent phenotype were successfully transmitted to one of the five isolates, Sm10. Three putative converted isolates of Sm10 were slow growing and developed atypical colony morphologies characteristic of the hypovirulent phenotype. These isolates were assayed for virulence and produced significantly smaller lesions than isolate Sm10 on detached leaves of Romaine lettuce. One of these putative converted isolates, designated Sm10T, was tested to confirm interspecific transmission of dsRNA. In northern hybridizations, dsRNA isolated from Sm10T hybridized with a digoxigenin-labeled cDNA probe prepared from dsRNA isolated from Ss275. Random amplified polymorphic DNA analysis confirmed that isolate Sm10T was derived from Sm10 and not from Ss275 or a hybrid of the two species. The dsRNA and hypovirulent phenotype were subsequently transmitted intraspecifically from Sm10T to Sm8. To our knowledge, this is the first report of interspecific transmission of dsRNA and an associated hypovirulent phenotype between fungal plant pathogens by hyphal anastomosis.

First Report of Angular Leaf Spot Caused by Phaeoisariopsis griseola on Bean in Ontario, Canada.

During the summer of 2000, brown, angular-shaped leaf spots, frequently surrounded by a chlorotic halo, were observed in commercial fields of green bean (Phaseolus vulgaris L.) in Ontario, Canada. Brown synematta (30 to 60 µm × 160 to 330 µm) and brown conidia (2 to 5 septate, usually curved, 5 to 7.3 µm × 35 to 66 µm) from the underside of diseased leaves were plated onto V8 agar. Within 3 to 4 days, dark olive green colonies formed, and after 10 to 14 days, white mycelial growth occurred on the upper surface of colonies, and colonies appeared gray. The causal agent was tentatively identified as Phaeoisariopsis griseola (Sacc.) Ferraris, the cause of angular leaf spot of bean, and this identification was later confirmed by the Centraalbureau voor Schimmelcultures, The Netherlands. New colonies of the fungus were started by streaking conidia across plates of V8 agar and new conidia were produced within 36 h. Conidial suspensions of 1 × 105 conidia/ml were sprayed onto leaves of green bean varieties Goldrush, Strike, Bronco, and Gold Mine. Plants were placed in a mist chamber at 20 ± 2°C for 11 days and then kept at high humidity for four more days. Lesions were observed 8 to 10 days after treatment and synematta developed 12 to 14 days after treatment. Disease symptoms and synematta were observed on all bean varieties tested. P. griseola was reisolated from inoculated plants, fulfilling Koch's postulates. To our knowledge, this is the first report of angular leaf spot occurring on P. vulgaris in Ontario.

Mutagenicity of cyanate, a decomposition product of MNU.

Knox reported that the short-term effects of the carcinogen methylnitrosourea (MNU) were due to the formation of its decomposition product, the cyanate ion. He showed that cell survival and DNA synthesis decreased as the concentration of MNU and the cyanate ion (NCO-) increased in the medium. Further, the product of MNU decomposition comigrated with NCO- when added to his chromatographic test system. However, Knox did not study the mutagenicity of MNU or its breakdown products. We compared the mutagenicity of MNU and potassium cyanate (KNCO) in mammalian cells. Our results demonstrate that, although it is toxic to cells, KNCO does not induce ouabain-resistant mutants in cultured Chinese hamster cells (V79).