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Developing a Screening Pipeline for the Identification of Phosphorus-Solubilizing Bacteria

By Juan Quijia Pillajo, Sachin Naik, and Michelle Jones

Phosphorus (P) is an essential nutrient with low availability for plant uptake. High media pH levels can cause the formation of insoluble compounds with calcium (Ca). Phosphorus solubilizing bacteria (PSB) can enhance P availability for plant uptake by producing organic acids to acidify the rhizosphere. The identification of PSBs requires both in-vitro and in-planta evaluations. In-vitro protocols allow for the screening of extensive bacterial collections, but the number of bacterial isolates that can be tested in the greenhouse is limited by the amount of space and time required to evaluate the plant responses to PSB inoculation. Digital phenotyping is an emerging tool for high throughput and precise evaluation of plant performance and health. 

This project aimed to develop a PSB screening pipeline using an in-vitro protocol and digital phenotyping with the TraitFinder (Phenospex) Greenhouse system. In-vitro P solubilization was quantified using the malachite-green assay. Eighteen isolates were identified as PSBs from a collection of around 1000 isolates. Digital phenotyping data was validated in a greenhouse experiment with Marigold (Tagetes patula) ‘Durango Orange,’ Radish (Raphanus sativus) ‘Cherry Belle,’ and Tomato (Solanum lycopersicum) ‘Bush Beef Steak.’ Plants were grown in a peat-based substrate and irrigated with 100 ppm N from a 15-0-15 fertilizer. P was provided weekly as insoluble Ca2(PO4 )3 via drench. Three in-vitro-identified PSB (OSU1, OSU2, and OSU3) and two microbial-based products (Lalrise Vita and MycoApply Endo) were tested. The growth index and shoot dry weight measurements were consistent with the digital biomass data calculated by TraitFinder. Lalrise Vita promoted growth in all plant species evaluated. Lalrise Vita also improved marigold health, which was assessed using the hue index, green leaf index (GLI), and plant senescence reflectance index (PSRI). The malachite-green assay and digital phenotyping are suitable tools for the rapid identification of phosphorus-solubilizing bacteria.