Diagnostic tests and their application in the management of soil- and water-borne oomycete pathogen species

Abstract

Oomycete diseases cause significant losses across a broad range of crop and aquaculture commodities worldwide. These losses can be greatly reduced by disease management practices steered by accurate and early diagnoses of pathogen presence. Determinations of disease potential can help guide optimal crop rotation regimes, varietal selections, targeted control measures, harvest timings and crop post-harvest handling. Pathogen detection prior to infection can also reduce the incidence of disease epidemics. Classical methods for the isolation of oomycete pathogens are normally deployed only after disease symptom appearance. These processes are often time consuming, relying on culturing the putative pathogen(s) and the availability of expert taxonomic skills for accurate identification, a situation that frequently results in either delayed application, or routine 'blanket' over-application of control measures. Increasing concerns about pesticides in the environment and the food chain, removal or restriction of their usage combined with rising costs have focussed interest in the development and improvement of disease management systems. To be effective, these require timely, accurate and preferably quantitative diagnoses. A wide range of rapid diagnostic tools, from point of care immunodiagnostic kits to next generation nucleotide sequencing have potential application in oomycete disease management. Here we review currently available as well as promising new technologies in the context of commercial agricultural production systems, considering the impacts of specific biotic and abiotic and other important factors such as speed and ease of access to information and cost effectiveness.

Pythium Damping-Off and Root Rot of Capsicum annuum L.: Impacts, Diagnosis, and Management

“…Immunological methods rely on antigen–antibody specificity. Although immunological methods for Pythium have been minimal because of the difficulty in producing species-specific antibodies [ 37 ], they have a better potential for use in point of care test systems operated by non-specialists [ 72 ]. Ray et al [ 73 , 74 ] used the polypeptides released during fungal infections as immunogens to develop polyclonal antibodies to detect early P. aphanidermatum infections in turmeric and ginger rhizomes, respectively.…”

Monitoring oomycetes in water: combinations of methodologies used to answer key monitoring questions

“…Trapped propagules can also be subjected to direct immunostaining procedures in situ on a membrane filter and observed by stereo microscope or a hand lens using the zoospore trapping immunoassay (ZTI), a procedure whereby captured, viable zoopsores and cysts are encouraged to germinate in situ prior to immuno-staining (Wakeham et al, 1997;Pettitt et al, 2002). The range of immunodiagnostic procedures of potential use in the testing and monitoring of irrigation water for oomycetes has been more fully reviewed by O'Brien et al (2009) and more recently by Wakeham and Pettitt (2017).…”

“…ZTI assays often require pre-filtration to remove debris, and the immunostaining procedure is more prone to interference than on dipsticks, especially when turbid samples are being assessed. ELISA and LFD test strips are not able to discriminate between viable and non-viable material (Wakeham and Pettitt, 2017). Whilst limited success has been achieved by coupling these procedures with a baiting step, there is a danger of false-positive tests as antigenic material has been found to attach to bait tissues in inoculated irrigation water previously subjected to heat, chlorination, or UV sterilization treatments (Wedgwood, 2014).…”

Phytophthora root rot of chickpea: inoculum concentration and seasonally dependent success for qPCR based predictions of disease and yield loss

“…A number of methods have been developed to determine oomycete inoculum concentration, including molecular methods that can detect low concentrations of oospores in soil (Wakeham and Pettitt 2017). For instance, a soil sievingcentrifugation method that concentrates oospores of Phytophthora capsici followed by quantitative PCR (qPCR) can detect 1 oospore/g soil (Pavon et al 2008).…”