The effects of temperature on zoospores of the crook root fungus Spongospora subterranea f.sp. nasturtii

Abstract

The effect of temperature on the release, survival, encystment and infectivity of Spongospora subterranea f.sp. nasturtii zoospores released from diseased watercress roots was studied. There was rapid, synchronized release of zoospores at 20°C followed by a steep decline in zoospore numbers. A similar trend occurred at 10° C and 15° C, although fewer zoospores were released and the subsequent decline was more gradual. In contrast, at 5°C very low numbers of zoospores were released over the first 5 days. Subsequently, zoospore release increased rapidly over the following 3 days and zoospore numbers were maintained at relatively high levels for a further 6 days. This duration of high zoospore numbers at 5°C was due to prolonged survival rather than continual release. When a uniform zoospore suspension released at IOC was transferred to 20·C zoospore numbers were found to decline rapidly over 6 days; the decline was less rapid at 15° C and IOC, taking 9 and 15 days, respectively. At 5°C zoospore numbers decreased slowly. Few zoospores encysted on roots at 20° C but increased numbers were found at 15°C and 10°C. There were significantly more diseased roots at 10° C than at 5,15 or 20° C. The lowest number of diseased roots was found at 20° C. The correlation between increased seventy of the disease in the field during the winter months and the effect of temperature on zoospores of S. subterranea f.sp. nasturtii is discussed.

Review: Powdery Scab of Potato—Increased Knowledge of Pathogen Biology and Disease Epidemiology for Effective Disease Management

“…A study by Fornier (1997) demonstrated that greater numbers of zoospores were released when sporosori where incubated at 15 and 25°C, compared with 5 and 10°C, but root infection of tomato plants was inhibited at 30°C. Claxton et al (1995) reported more diseased watercress roots at 10°C than at 5, 15 or 20°C, with the lowest number at 20°C, when they inoculated soil with Ssn sporosori. Both Fornier (1997) and Claxton et al (1995) observed a longer duration of relatively high concentrations of swimming zoospores in sporosorus suspensions at lower than at higher temperatures, explained by Claxton et al (1995) as resulting from prolonged survival rather than continual zoospore release.…”

“…Claxton et al (1995) reported more diseased watercress roots at 10°C than at 5, 15 or 20°C, with the lowest number at 20°C, when they inoculated soil with Ssn sporosori. Both Fornier (1997) and Claxton et al (1995) observed a longer duration of relatively high concentrations of swimming zoospores in sporosorus suspensions at lower than at higher temperatures, explained by Claxton et al (1995) as resulting from prolonged survival rather than continual zoospore release. In an experiment in which potato plants were grown in inoculated sand under controlled conditions, de Boer (2000a) showed that the incidence and severity of powdery scab on progeny tubers was greatest at 12.5°C, intermediate at 15°C, and low at 17.5 and 20°C, and no disease occurred at 10°C.…”

Development of a PCR‐based diagnostic test for Spongospora subterranea f.sp. nasturtii, the causal agent of crook root of watercress (Rorippa nasturtium‐aquaticum)

“…nasturtii has been developed. Claxton et al . (1995) described a system for releasing zoospores from crooked roots placed in a solution of nutrients, which provides a crude method of quantification, but this approach is laborious and takes at least 3 days to perform.…”

“…nasturtii has been developed. Claxton et al (1995) described a system for releasing zoospores from crooked roots placed in a solution of nutrients, which provides a crude method of quantification, but this approach is laborious and takes at least 3 days to perform. Approaches based on monoclonal or polyclonal antibodies have not been attempted on this pathogen, but they have been tried with other plasmodiophorids: such attempts to use antibody-based assays for plasmodiophorid detection have frequently encountered difficulties with sensitivity in soil (Harrison et al, 1993;Wallace et al, 1995;Wakeham & White, 1996;Walsh et al, 1996) and an inability to distinguish between live and dead resting spores (Harrison et al, 1993;Walsh et al, 1996), although this latter limitation may also apply to DNA.…”