Confirmatory, Non-Invasive and Non-Destructive Diagnostics of Plant Biotic and Abiotic Stresses Using A Hand-Held Raman Spectrometer
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Global food security is one of the most important needs of our civilization and its importance will only increase in the future. Currently, over a billion people suffer from a lack of sufficient nutrition and, by 2050, we will need 70% more food.1 These problems can be potentially eased by an expansion of agricultural land areas through conversion of forests. However, this approach is inefficient and destructive to nature. Another strategy is to develop methodology for timely detection and identification of biotic and abiotic stresses. Precisely identifying plant diseases will allow for a selective pathogen treatment in certain area of farm fields. Such a precise disease-treatment approach is economically advantageous and has the potential of saving up to 50 % of the total agricultural yield worldwide.2 There are several molecular and imaging techniques that can be used to detect biotic and abiotic stresses. For instance, polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) are commonly used for the confirmatory diagnostics of plant diseases. However, these molecular methods have their own limitations. ELISA, for instance, including double and triple antibody ELISA, has low sensitivity, photobleaching instability and poor specificity to related pathogen strains.3-4 PCR has limited portability, high labor and cost requirements, need of specific expertise, difficulty in screening an entire orchard with PCR analysis, and is essentially destructive to the analyzed specimen.5-7 There are several imaging techniques, such as hyperspectral imaging and thermography, which potentially can be used for indirect detection of biotic and abiotic stresses on plants. These techniques allow for fast imaging of broad field areas. However, they suffer from poor specificity since the pathogen detection is based on a change in plant color or temperature. Obviously, such changes could be also caused by a variety of different factors such as heat and nutrient deficiencies. Additionally, despite quick imaging, data analysis typically requires several weeks before conclusions can be drawn.8 Accounting for the fast growth of plants and rapid proliferation of plant diseases, such slow data analysis turnaround drastically decreases practical applications of hyperspectral imaging, thermography and other imaging techniques.These limitations recently catalyzed a push toward developing minimally invasive and substrate general techniques that can be used in the field for confirmatory detection and identification of both biotic and abiotic stresses on plants.
