R. H. Johnston

Applying Real-Time Quantitative PCR to Fusarium Crown Rot of Wheat

Fusarium crown rot (FCR) of wheat is a persistent problem that causes significant losses worldwide. In Montana, FCR is caused primarily by Fusarium culmorum and F. pseudograminearum. Recently, a real-time quantitative PCR (QPCR) assay was developed for FCR using primers and probes specific for a segment of the trichodiene synthase (tri5) gene. The purpose of this study was to determine the utility of QPCR for accessing FCR severity on wheat in field experiments. In 2004 and 2005, plots of spring and durum wheat were inoculated with varying levels of F. pseudograminearum oat inoculum and grown under rain-fed conditions. Two weeks prior to harvest, plants were collected from the plots and assessed for FCR severity and analyzed by QPCR for Fusarium DNA quantities. Disease severity scores (DSS) and Fusarium DNA quantities were positively correlated with each other for all three cultivars in 2004 but for only the durum cultivar in 2005 (P < 0.05). In 2004, grain yields for both spring wheat cultivars were negatively correlated with Fusarium DNA quantities (P > 0.05). When DSS and Fusarium DNA quantities negatively correlated with yield, both measurements were comparable in predicting yield reduction (R = -0.64 and -0.77, respectively). Results indicate that this QPCR assay is effective in measuring FCR severity in wheat.

Combined biological and chemical seed treatments for control of two seedling diseases of Sh2 sweet corn

Experiments were conducted in both the glasshouse and in the field to determine if biological and chemical control agents could be used together on sweet corn (Zea mays L.) seed to control Pythium ultimum damping-off or Penicillium oxalicum seedling disease. Pseudomonas aureofaciens AB254 and Pseudomonas sp. AB842 were used for control of P. ultimum and P. oxalicum, respectively. Metalaxyl seed treatment for control of P. ultimum was used at rates from 100 to 0.01% of the recommended rate either alone or in combination with P. aureofaciens AB254. Imazalil seed treatment for control of P. oxalicum was used at rates from 100 to 1% of the recommended rate either alone or in combination with Pseudomonas sp. AB842. In field tests, combining a chemical treatment with the biological agent did not affect the efficacy of disease control. Nor did combining low rates of chemical with the biocontrol agent increase the efficacy or reliability of disease control.

Survival of Teliospores of Tilletia indica in Soil

This study was conducted to assess survival of Tilletia indica teliospores in a location in the northern United States. Soils differing in texture and other characteristics were collected from four locations, equilibrated to -0.3 MPa, and infested with teliospores of T. indica to give a density of 103 teliospores per gram of dry soil. Samples (22 g) of the infested soil were placed in 20-μm mesh polyester bags, which were sealed and placed at 2-, 10-, and 25-cm depths in polyvinyl chloride tubes containing the same field soil as the infested bags. Tubes were buried vertically in the ground at Bozeman, MT, in October 1997. Soil samples were assayed for recovery and germination of T. indica teliospores 1 day and 8, 20, and 32 months after incorporation of teliospores into soil. The rates of teliospores recovered from soil samples were 90.2, 18.7, 16.1, and 13.3% after 1 day and 8, 20, and 32 months after incorporation of teliospores into soil, respectively, and was significantly (P < 0.01) affected by soil source. The percentage of teliospore recovery from soil was the greatest in loam soil and lowest from a silt loam soil. The rate of teliospores recovered from soil was not significantly affected by depth of burial and the soil source-depth interaction during the 32-month period. The percentage of germination of teliospores was significantly (P < 0.01) affected by soil source and depth of burial over the 32-month period. The mean percentage of teliospore germination at 1 day, and 8, 20, and 32 months after incorporation into soils was 51.3, 15.1, 16.4, and 16.5%, respectively. In another experiment, samples of silty clay loam soil with 5 × 103 teliospores of T. indica per gram of soil were stored at different temperatures in the laboratory. After 37 months of incubation at 22, 4, -5, and -18°C, the rates of teliospore recovered from soil were 1.6, 2.0, 5.7, and 11.3%, respectively. The percentage of spore germination from soil samples was highest at -5°C. Microscopy studies revealed that disintegration of teliospores begin after breakdown of the sheath-covering teliospore. The results of this study showed that teliospores of T. indica can survive in Montana for more than 32 months and remain viable.

SOURCES OF RESISTANCE TO CEPHALOSPORIUM GRAMINEUM IN TRITICUM AND AGROPYRON SPECIES

SummaryResistance to the soil-borne pathogen Cephalosporium gramineum was evaluated in Agropyron elongatum, A. intermedium. A. intermedium var. trichophorum, an Agrotriticum, and eight species of Triticum. Only A. elongatum and A. intermedium showed high levels of resistance. Agrotriticum (56 chromosomes) was resistant too. High resistance to C. gramineum is available, but its utilization will probably require the use of chromosome substitution techniques to transfer the resistance into an agronomically useful wheat.

Comparison of pathogenicity of the Fusarium crown rot (FCR) complex (F. culmorum, F. pseudograminearum and F. graminearum) on hard red spring and durum wheat.

Fusarium species involved in the Fusarium crown rot (FCR) complex affect wheat in every stage of development from seedling to grain fill. This study was designed to compare the aggressiveness of the FCR complex members including F. culmorum, F. pseudograminearum and F. graminearum in causing seedling blight, decreased plant vigour and crown rot. To assess their relative pathogenicity, two hard red spring wheat cultivars and two durum wheat cultivars were inoculated in the field with five isolates from each of the three species for two years. Significant differences in patterns of pathogenicity were identified. In particular, F. culmorum caused greater seedling blight while F. pseudograminearum and F. graminearum caused greater crown rot. Greatest yield reductions were caused by F. pseudograminearum. Cultivar differences were identified with respect to seedling disease and late season crown rot. No interactions were identified between cultivar performance and isolates or species with which they were challenged.