Severity Of Powdery Scab Research Articles

Relationship between Spongospora subterranea f. sp. subterranea soil inoculum level, host resistance and powdery scab on potato tubers in the field

The relationship between initial soil inoculum level of Spongospora subterranea f. sp. subterranea (Sss) and the incidence and severity of powdery scab on potato tubers at harvest was investigated. In all experiments soil inoculum level of Sss (sporeballs/g soil) was measured using a quantitative real‐time PCR assay. Of 113 commercial potato fields across the UK, soil inoculum was detected in 75%, ranging from 0 to 148 Sss sporeballs/g soil. When arbitrary soil inoculum threshold values of 0, <10 and >10 sporeballs/g soil were set, it was observed that the number of progeny crops developing powdery scab increased with the level of inoculum quantified in the field soil preplanting. In four field trials carried out to investigate the link between the amount of inoculum added to the soil and disease development, disease incidence and severity on progeny tubers was found to be significantly (P < 0·01) greater in plots with increasing levels of inoculum incorporated. There was a cultivar effect in all years, with disease incidence and severity scores being significantly greater in cvs Agria and Estima than in Nicola (P < 0·01).

The Identification and Detection of Spongospora subterranea and Factors Affecting Infection and Disease

Powdery scab caused by Spongospora subterranea is a serious disease, affecting both the quality and quantity of ware and seed potatoes, particularly in northern Britain where soil conditions are conducive to disease development. To enable accurate quantification of S. subterranea DNA for epidemiological studies, a real-time PCR assay specific to this pathogen was developed. This assay could reliably detect and quantify DNA from sporeballs, zoospores and plasmodia/zoosporangia of S. subterranea. The assay was used to measure the viability of sporeballs in soil, was combined with a tomato bait plant technique in order to study zoospore release and was used to study infection levels in potato under various environmental conditions. Both the incidence and severity of powdery scab were found to be influenced by temperature, soil type and soil moisture regime when tested under controlled conditions. Soil inoculum level did not have a significant effect on infection and disease development and even low levels of inoculum were regularly found to result in severe disease symptoms. Evidence from A GB-wide trial and a five year survey in England and Wales confirmed that there is no simple or consistent relationship between powdery scab inoculum on seed and disease developing on the progeny crop. Disease risk appears to be more related to the relative conduciveness of environmental conditions rather than inoculum level. Integration of control measures is likely to be the most effective way for growers to reduce the impact of the disease.

The use of molecular diagnostics to investigate the epidemiology of potato diseases

In recent years, quantitative molecular diagnostic assays based on real-time PCR have been developed for many pests and pathogens of potato. In addition, simple sequence repeat markers have been developed and used to track isolates of Phytophthora infestans. These diagnostic assays are now being used as tools to study unresolved questions in the epidemiology of potato diseases including late blight, powdery scab and black dot. Examples of various investigations designed to examine the relative contribution of seed and soil-borne inoculum in causing black dot and powdery scab on progeny tubers, the effect of environmental factors on the incidence and severity of powdery scab and the survival of asexual and sexual inoculum of P. infestans in soil are described. Consideration is given to the development of appropriate diagnostic assays, their use in conjunction with relevant and robust sampling techniques, and the interpretation of results to inform disease risk assessment and control strategies through industry collaboration.

Effect of planting date and inoculum level on incidence and severity of powdery scab on potato

Powdery scab incidence and severity was examined on six potato cultivars planted at two different dates in a naturally infested field. There were two sub-plots; one where seed was exposed prior to planting to spores ofSpongospora subterranea from scabby peels, which were then added to the furrow at planting, and another where seed was exposed only to natural inoculum within the field. The later planting data reduced incidence and severity, but there were no differences between sub-plots. All cultivars became infected, but ‘Rosa’ was the most susceptible and ‘Katahdin’ the most resistant.

Incidence and severity of powdery scab on potatoes in Pennsylvania

Studies were conducted in Potter Co., Pennsylvania to investigate the effect of powdery scab (Spongospora subterranea) on five potato cultivars (Norchip, Rosa, Kennebec, Katahdin, and Monona) at two planting dates. Soil temperature was within the range of 15–18 C and soil moisture was within 15–19% based on dry weight throughout the season. The effect of planting date was significant at each disease assessment, except for the severity on the fourth assessment. By the end of the season, incidence of scab was 66% or more for all cultivars. Rosa, Kennebec and Katahdin had a greater scab incidence over both planting dates and a greater severity at the first planting date than Monona and Norchip.