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Articles by G.D. Turnbull
Total Records ( 4 ) for G.D. Turnbull
  K.F. Chang , S.F. Hwang , A.H. Khadhair , H.U. Ahmed , S.E. Strelkov , M. Deyholos , G.D. Turnbull and J. Feng
  During the summer of 2003 and 2004, a total of 58 isolates of Ascochyta rabiei were collected from chickpea plants grown in southern Alberta, Canada. RAPD analysis of genomic DNA extracted from these isolates was conducted using six short sequence primers (OPA-03, OPA-13, OPB-07, OPC-01, OPC-20 and OPJ-15) and analyzed to establish the genetic relationship and distance between isolates. A total of 75 bands were polymorphic. The 58 isolates were found to belong to five genotypes, indicating that the A. rabiei population of southern Alberta is genetically diverse. No relationship was found between the genotype groupings obtained through RAPD analysis and previously determined pathotype classifications of the same isolates.
  S.F. Hwang , H.U. Ahmed , K. Ampong-Nyarko , S.E. Strelkov , R.J. Howard and G.D. Turnbull
  Rhodiola (Rhodiola rosea) is a plant with adaptogenic properties and is suitable for cultivation in Alberta, Canada. Disease surveys indicated the occurrence of root rots in rhodiola plantations in the Province. A total of 74 fungal isolates were associated with discoloration and rotting in the crown and root regions of the plants. Among these, 15 isolates were identified as Fusarium sp., three as Pythium sp. and eight as Rhizoctonia sp. This is the first report of root rot in rhodiola in Alberta, Canada. These soil-borne pathogens are the potential threat to the quality and quantity of rhodiola production. Experiments were conducted to determine the effect of vesicular-arbuscular mycorrhizal fungi and these soil pathogens on rhodiola growth and development under greenhouse conditions. Overall results indicated that Fusarium, Pythium and Rhizoctonia sp. are all capable of reducing rhodiola biomass. However, biomass was significantly higher when vesicular-arbuscular mycorrhizal fungi were applied in conjunction with these pathogens or in non-inoculated controls. This suggests that vesicular-arbuscular mycorrhizal fungi could be used as a management tool for the control of seedling root rot diseases of rhodiola.
  S.F. Hwang , H.U. Ahmed , B.D. Gossen , H.R. Kutcher , S.A. Brandt , S.E. Strelkov , K.F. Chang and G.D. Turnbull
  Impact of long-term crop rotations on populations of soilborne pathogens in the genera Fusarium, Pythium and Rhizoctonia and on canola seedling establishment and development was evaluated under controlled conditions. Soil samples were collected from two crop rotation experiments conducted at two sites in Saskatchewan, Canada. A part of the 2006-soil sample of each rotation was sterilized to compare canola seedling growth with and without soilborne pathogens. With 2007-soil, the sterilization treatment was replaced with a fungicide seed treatment (Apron Maxx) to assess the potential to reduce seedling diseases. Populations of Fusarium, Pythium and Rhizoctonia sp. were estimated in the soil of each rotation using dilution plating onto selective media for each fungus. Higher seedling emergence and increased growth of canola were obtained in the sterilized soil or due to seed treatment. Fusarium was the predominant genus followed by Pythium and Rhizoctonia sp. in the soil of both sites. This study suggests that diverse crop in the rotation may reduce the populations of Fusarium, Pythium and Rhizoctonia in the soil and may contribute to improve the overall growth of canola.
  H.U. Ahmed , S.F. Hwang , G.D. Turnbull , S.E. Strelkov and B.D. Gossen
  Seedling blight caused by Rhizoctonia solani Kühn substantially reduces stand establishment and seed yield of canola (Brassica napus L.) in western Canada. The effect of crop residue on soil populations of R. solani and canola seedling blight was examined under field, greenhouse and laboratory conditions. Field plots were established with inoculation or noninoculation with R. solani as the main plot and barley, canola, oat and field pea residues as the sub-plots. Soil samples were collected from each subplot for analysis in a greenhouse bioassay and laboratory assay of R. solani population before seeding canola. The crop residue effect was not significant. Under inoculation with R. solani, the yield was consistently greater when canola was grown on barley residue compared to the canola residue over two-year trials, although oat and pea residue contributed to greater yield. Without inoculation, canola yield was greatest when grown on barley residue, intermediate on oat and pea and the least on canola in the first trial and in the second trial greater yield was obtained on barley and oat residues compared to other residues. In the greenhouse bioassay, canola seedling emergence was greater, while damping off and root rot were less severe, following barley or oat compared to canola or field pea in both inoculated and non-inoculated treatments. Populations of Rhizoctonia were lower following barley or oat relative to canola or field pea. Crop rotation and incorporation of barley or oat residue between canola crops may be a useful strategy to reduce seedling blight of canola.
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