Systematic grid-based detection and quantification of six major strawberry pathogens for nursery fields

The global strawberry industry is very competitive and involves clonal propagation of planting stock, shipped to fruit production fields. This plant movement presents various plant health challenges where nursery stock, a critical step in the fruit production pipeline, must be as clean as possible. Pests and pathogens from nurseries, including symptomless plants and those with very low inoculum densities, can be introduced to fruiting fields resulting in plant damage and significant economic loss. Routine scouting as well as conventional diagnostic techniques, including plating, baiting, grow-outs, and a few molecular assays, are routinely used at multiple points of the propagation cycle to test for the presence of important pathogens. However, these techniques can be labor intensive, low volume, and can take several weeks to complete, leading to delayed operational decisions. We successfully developed and implemented a protocol for targeted quantification of the main major strawberry pathogens Colletotrichum acutatum, Fusarium oxysporum f. sp. fragariae, Macrophomina phaseolina, Phytophthora cactorum, Verticillium dahliae, and Xanthomonas fragariae. We utilized a systematic grid plant sampling plan in the nursery field totaling hundreds of acres. Samples are collected prior to plant harvest and subjected to high volume DNA extraction and purification assays before molecular diagnostics using pathogen-specific quantitative PCR. Using this protocol, pathogens can be detected and estimated even at extremely low DNA levels and field scale geospatial information captured. The information obtained can provide plant quality assurance and be used by nurseries to capture geospatially tagged plant and soil health information over time to make timely management decisions to maximize the quality of plants. While not replacing classical plant health approaches, field grid-based pathogen quantification can be deployed as an additional tool to increase quality and add value to strawberry production.