Smartphones are increasingly used as field labs by potato agronomists, combining CRISPR enzymes, isothermal DNA amplification, and optical readouts. These platforms, already demonstrated for late blight, are now being adapted for early blight (Alternaria solani), a disease that reduces yields and increases spray costs.
Early blight typically begins with small, dark lesions on lower leaves, but visual diagnosis can be uncertain and lead to unnecessary fungicide applications. A rapid, field-based molecular test would support more precise spray timing.
A practical workflow integrates recombinase polymerase amplification (RPA), CRISPR-Cas12a detection, and smartphone readouts. RPA amplifies DNA fragments in about 20 minutes at 37–42 °C. Cas12a, guided by RNA sequences, activates collateral cleavage that produces either a fluorescent or colorimetric signal. Readouts are made using clip-on optics or simple colorimetry apps. Sample preparation methods include simplified buffers, paper dipsticks, and microneedle patches that extract DNA directly from leaf tissue within one minute.
Recent studies provide evidence for feasibility. In 2025, a smartphone-integrated RPA-CRISPR-Cas12a system detected Phytophthora infestans (late blight) within 60–90 minutes and at concentrations of around 2 pg/µL, prior to visible symptoms. Another study validated RPA–CRISPR detection of Alternaria species from wheat, confirming assay specificity. Smartphone-based colorimetry platforms such as RAVI-CRISPR and the MagicEye app have also demonstrated reliable performance under field conditions.
A field-ready early blight workflow would involve microneedle sampling, 20 minutes of RPA amplification, 10–20 minutes of CRISPR detection, and analysis via smartphone apps. Decisions could be made in under 90 minutes, allowing fungicide applications to be delayed or advanced based on the confirmed presence of A. solani.
Analytical performance depends on guide design to avoid cross-reactivity with A. alternata and other foliar pathogens. Specificity, robustness against inhibitors in potato tissue, and contamination control remain practical considerations. Temperature-stable reagents, sealed-tube chemistries, and standardized phone optics are being developed to reduce variability.
Compared to scouting and hyperspectral imaging, CRISPR diagnostics directly detect pathogen DNA, providing confirmation rather than indirect stress signals. While PCR remains the laboratory standard, CRISPR offers a portable, sequence-specific option with faster turnaround than LAMP assays.
Implementation challenges include cost, which remains higher than LAMP, and the need for validation data before processors and buyers adopt results into supply-chain protocols. However, multiplex kits could expand diagnostics to late blight, blackleg, and soft rot pathogens, turning a single smartphone platform into a broader field lab.
Researchers note that climate pressure and market uncertainty are accelerating the adoption of precision diagnostics. Smartphone-CRISPR assays for early blight are expected to move from experimental prototypes to practical field kits within the next one to two years.
Source: Potato News Today