|Van Es, H|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/2003
Publication Date: 9/1/2003
Citation: Davidson, L.E., Schindelbeck, R.R., Van Es, H.M., Gray, S.M., Bergstrom, G.C. 2003. Using air pressure cells to evaluate the effect of soil environment on the transmission of wheat soil-borne mosaic virus. Phytopathology. 93:1131-1136. Interpretive Summary: Soil-borne viruses of wheat are prevalent in most areas of the United States and cause significant yield loss, especially in areas with cool, wet climates during the planting season. These viruses are transmitted by soil-inhabiting protozoans and specifically by swimming zoospores that move between plant roots during saturated soil conditions. These are very much temperature dependent diseases which makes field studies difficult due to erratic and unpredictable weather conditions at the time when plant infection must take place. Controlled environmental studies have proven difficult due to an inability to identify precise conditions that allow virus transmission and plant infection to occur. There is some evidence to suggest these two phenomenon can be independent and that they require distinct environment conditions. Our research brought together soil physics and plant virology to exploit a technique widely used to study soil structure and its capacity to retain moisture. Air pressure cells were used to equilibrate soil at specific water capacities for specific times. Additionally, soil cores with known moisture content could be maintained at consistent or variable temperatures. The precise control of these two properties allowed us to determine the conditions that were optimal for the release of zoospores, the movement of zoospores between roots and the infection of roots by the protozoan and the virus. Knowing the range of optimal transmission and infection parameters will allow the development and testing of predictive models that may be useful in developing and implementing soil-borne virus disease management strategies.
Technical Abstract: A novel approach was implemented to address epidemiological questions and to devise a rapid screen for assessing chemical efficacy in preventing infection by a prevalent soilborne disease. Field soil infested with Wheat soilborne mosaic virus (WSBMV) and its presumed vector Polymyxa graminis Ledingham was used to investigate three epidemiological factors of viral transmission: soil matric potential, temperature, and duration required for transmission. Using an air pressure cell apparatus precise soil matric potentials were established at -1, -5, -20, and -40 kPa in soil cores infested with WSBMV and planted to wheat (Triticum aestivum). At these soil matric potentials, all pores equal to or smaller than 219.0, 55.9, 14.7, and 7.4 µm, respectively, would be water-filled. Of the four soil matric potentials tested, the only non-conducive treatment for WSBMV transmission was -40 kPa (the driest), which corresponds to a largest filled pore size that excludes movement by P. graminis zoospores. By starting plants at -40 kPa for 10.5 days then watering them to conducive matric potential, we found that WSBMV transmission occurs between 12-24 hours at 10 and 15C, and within 36 hours at 20C. No significant transmission occurred within 96 hours at 6.5C. In another series of experiments, transmission of Wheat spindle streak mosaic virus did not occur at 15C (the only transmission temperature tested), suggesting either that a different vector is involved or that WSSMV is unable to establish infection at 15C.