Paradigm Shift in Plant Disease Diagnostics: A Journey from Conventional Diagnostics to Nano-diagnostics

Abstract

Agriculture struggles to support the rapidly growing global population but catastrophic or chronic losses caused by plant disease pose a potential threat to production and quality of food, fibre and biofuel crops. Plant disease diagnosis and detection of plant pathogen are critical and integral part of successful disease management and can prove to be an important quarantine tool for transboundary movement of plant material. The demand for rapid, accurate, sensitive, standard, high throughput and simultaneous detection assays of plant pathogens has risen in the last few decades due to intensive monocropping. Early, quick and cost effective identification can only serve as a measure for management, minimizing further introduction or spread of a plant pathogen. In the present scenario due to emerging and re-emerging plant pathogens, Phytopathologists have moved from the more traditional use of biological indicator hosts to molecular and nano-diagnostics. Conventional methods for plant pathogen detection relied on identification of disease symptoms, isolation, culturing, identification by morphology (fungi), biochemical tests (bacteria) and physical properties, transmission assays, host range, etc. (viruses). These conventional methods suffer from an array of: requirement of skilled taxonomists for reliable identification of the pathogen, laborious, less sensitive, and relatively high time consumption. However, the advancement created by science in the field of biotechnology and molecular biology have revolutionized the field of plant disease diagnostics, providing a panel of methodologies, tools and techniques. Several techniques have been developed which have found application in plant pathogen diagnosis; these include serological techniques: enzyme linked immuno-sorbent assay (ELISA), which drastically increased the speed in which pathogen could be detected in vivo and molecular techniques: polymerase chain reaction (PCR) in the mid 1980s which enables amplification of pathogen genome region, thus increasing the sensitivity of pathogen detection. There has been an exponential increase in the number of protocols based on molecular tools such as second generation PCR known as the real-time PCR and microarrays which allows unlimited multiplexing capability. Increased use of automation and user-friendly software makes these technologies more widely available. High throughput sequencing platforms (Next generation sequencing) and lateral flow assays are also gaining attention for detection of pathogens. The upcoming introduction of quick on-site portable devices for diagnosis of pathogens using nano-based kits and development of innovative devices such as electronic nose is gaining momentum and has potential applications. Despite availability of an array of techniques, acceptability is required by scientific community for routine plant disease diagnosis.