In a field trial conducted during the 2024–2025 Kharif season in Uttarakhand, India, researchers evaluated the effects of pre-sowing seed priming with the synthetic strigolactone analog (-)-epi-GR24 on the growth, productivity, and rhizosphere soil dynamics of Vigna mungo (urd bean). Seed treatment using intermediate concentrations of 5 µM and 10 µM significantly enhanced field establishment, vegetative vigor, root development, nodulation, and grain yield compared with untreated control plots. The study demonstrated that strigolactones, a class of carotenoid-derived phytohormones traditionally recognized for regulating plant architecture, can also stimulate rhizosphere microbial activity and improve soil nutrient availability under field conditions. However, the trial observed non-linear responses where higher concentrations failed to deliver proportional benefits, underscoring the importance of dosage optimization in phytohormone applications.
Vigna mungo represents an essential pulse crop extensively cultivated throughout South and Southeast Asia, serving as an indispensable dietary source of protein, minerals, vitamins, and dietary fiber that plays a critical role in mitigating malnutrition in developing nations. As a leguminous species, urd bean enhances soil fertility through symbiotic nitrogen fixation with rhizobia, thereby decreasing reliance on synthetic nitrogen fertilizers. Maintaining robust soil microbial communities that facilitate organic matter decomposition, nutrient cycling, and disease suppression is critical for supporting resilient crop growth under common environmental challenges such as drought and nutrient deficiency. Pre-sowing seed priming, which involves the controlled hydration of seeds in bioactive solutions followed by redrying prior to radical emergence, offers a cost-effective technique to initiate early metabolic processes, synchronize germination, and improve seedling vigor under field conditions.
Strigolactones function as crucial phytohormones that regulate shoot branching, root architecture, and rhizosphere signaling, promoting mutualistic symbioses with arbuscular mycorrhizal fungi and rhizobia to improve phosphorus and nitrogen uptake. Previous studies had shown that synthetic analogs like GR24 enhance antioxidant defenses, fresh biomass, and stress resilience in crops such as maize, cucumbers, and sunflowers under saline or drought environments. However, earlier investigations predominantly focused on plant morphological traits or stress responses under controlled settings, leaving the integrated plant-rhizosphere system following seed priming underexplored in grain legumes. In particular, limited field evidence existed regarding how seed-applied (-)-epi-GR24 simultaneously influences seedling establishment, root development, nodule formation, and rhizosphere enzyme activity. To address this knowledge gap, the authors evaluated a range of (-)-epi-GR24 concentrations between 1 and 20 µM to identify agronomically effective application levels in V. mungo.
The field trial was conducted at the research farm of Graphic Era Hill University in Dehradun, Uttarakhand, India (latitude 30.111771 N, longitude 77.883643 E), during the 2024–2025 Kharif season. The experimental area was organized according to a randomized block design consisting of five treatments replicated across four blocks, covering a total surface of 288 square meters. Individual experimental plots measured 6 square meters each, separated by 0.5-meter buffer zones, with each replication block spanning approximately 32 square meters. Throughout the crop growth cycle, the experimental site experienced mean minimum and maximum temperatures of 21.2 degrees Celsius and 26.53 degrees Celsius, respectively, a mean relative humidity of around 80 percent, and zero millimeters of total rainfall. Prior to sowing and treatment application, representative composite soil samples were collected from a depth of 0 to 15 centimeters to characterize baseline physical, chemical, and biological soil conditions.
The plant material evaluated was Vigna mungo cultivar PU 31, an authorized high-yielding variety obtained from Govind Ballabh Pant University of Agriculture and Technology in Pantnagar, Uttarakhand. Introduced in 2005, cultivar PU 31 matures within 75 to 80 days, possesses bold, shiny black seeds, and demonstrates resistance to Yellow Mosaic Virus and rust. Synthetic strigolactone analog (-)-epi-GR24, with a molecular weight of 298.294 grams per mole, was provided by Professor Christopher S. P. McErlean from the University of Sydney. For treatment application, 10-gram seed lots were soaked for 24 hours at room temperature in 50 milliliters of solution containing 0, 1, 5, 10, or 20 µM (-)-epi-GR24, surface-dried, and shade-dried for 5 to 6 hours before sowing on August 9, 2024, at a 3 to 5 centimeter depth with 10-centimeter spacing. Field preparation included double cultivator ploughing, harrowing, levelling, basal NPK fertilization at a 120:60:60 ratio, and manual weeding without chemical pesticide interventions.
Soil biological health was evaluated by monitoring microbial populations and dehydrogenase activity, an indicator of microbial oxidative metabolism. Dehydrogenase activity was quantified using the reduction of 2,3,5-triphenyltetrazolium chloride to triphenylformazan based on the Casida analytical method. Soil samples of 3.0 grams were combined with 0.2 grams of calcium carbonate, 1 milliliter of 3 percent triphenyltetrazolium chloride, and 2.5 milliliters of distilled water, followed by incubation at 37 degrees Celsius for 24 hours. The produced triphenylformazan was extracted using 10 milliliters of methanol, filtered, and analyzed spectrophotometrically at 485 nanometers, with activity expressed as micrograms of triphenylformazan per hour per gram of soil. Soil chemical traits, including organic carbon, pH, electrical conductivity, available nitrogen, and available phosphorus, were also determined alongside microbial counts. Experimental data were statistically analyzed via one-way analysis of variance using the Web-Based Agricultural Statistical Software Package developed by ICAR-CCARI, separating treatment means using Tukey’s Honestly Significant Difference test at p < 0.05.
Seedling emergence and crop stand assessments recorded at 30 days after sowing revealed significant variations in plant population per plot resulting from strigolactone priming. Plots sown with seeds primed with 5 µM (T2) and 10 µM (T3) (-)-epi-GR24 recorded the highest mean plant populations, reflecting superior crop establishment compared to the water-primed control. However, the plant population response was non-linear, as raising the concentration further to 20 µM (T4) failed to produce a corresponding improvement in stand density. From an agronomic perspective, establishing an adequate and uniform plant stand is critical because early seedling density forms the structural foundation for subsequent vegetative canopy growth and light capture. Plant height measurements followed a similar non-linear pattern, wherein intermediate concentrations of 5 µM and 10 µM produced significantly greater plant height than control treatments, whereas the highest 20 µM treatment showed a comparatively diminished vegetative response, demonstrating that moderate strigolactone concentrations favor shoot elongation.
Morphological evaluations revealed distinct concentration-dependent and trait-specific responses between above-ground organs and root system development. Priming with 5 µM (-)-epi-GR24 proved most effective for foliage development and root biomass, yielding the maximum leaf production of approximately 24 leaves per plant, alongside the greatest root length, root fresh weight, and root dry weight among all evaluated treatments. In contrast, symbiotic root nodulation reached its highest value under the 10 µM treatment, which generated approximately 66 root nodules per plant, significantly exceeding the nodule counts recorded in the untreated control and lower concentration groups. This divergence between the optimal priming concentration for leaf and root biomass accumulation and the dosage maximizing nodule formation illustrates the trait-specific regulatory actions of strigolactones. Elevating the concentration to 20 µM did not further stimulate root length, biomass accumulation, or nodulation, confirming that supra-optimal hormone exposure does not confer additive vegetative advantages.
Crop yield assessments demonstrated that seed priming with (-)-epi-GR24 exerted a pronounced, non-linear influence on both biological and economic yield attributes. Treatment with 10 µM (-)-epi-GR24 (T3) proved to be the most effective intervention for overall productivity, achieving a maximum seed yield of 35.27 grams per plant and a biological yield of 131.77 grams per plant. In comparison, non-primed control plants (T0) recorded a seed yield of 32.13 grams per plant and a biological yield of 94.63 grams per plant. Increasing the priming concentration to 20 µM led to an evident reduction in productivity, producing only 31.13 grams per plant of seed yield and 107.67 grams per plant of biological yield, values lower than those obtained under the 10 µM treatment. These quantitative comparisons verify that an intermediate concentration of 10 µM represents an agronomically optimal priming threshold for balancing reproductive partitioning and whole-plant vegetative biomass in urd bean.
Post-harvest rhizosphere soil analyses demonstrated that pre-sowing seed priming generated measurable secondary benefits within the root-associated soil environment. Plots planted with seeds primed at 5 µM and 10 µM exhibited substantial increases in biological activity, evidenced by higher populations of culturable bacteria and fungi compared to control plots, with bacterial abundance reaching its peak in the 5 µM group. Concurrently, soil dehydrogenase activity showed marked enhancement under optimized strigolactone treatments, peaking in the 10 µM treatment alongside elevated concentrations of organic carbon, available nitrogen, and available phosphorus. The simultaneous improvements observed in rhizosphere microbial numbers, enzymatic activity, and macronutrient availability suggest a functional relationship between strigolactone-mediated plant stimulation and rhizosphere biological functioning.
Despite these positive experimental outcomes, the authors highlighted important methodological boundaries and emphasized the need for cautious interpretation of the preliminary field data. The experiment was conducted at a single geographical site in Dehradun across only one Kharif season, meaning that multi-location and multi-season trials are required to confirm the consistency of these priming responses under diverse soil types and seasonal climates. Furthermore, the internal physiological and molecular mechanisms driving the observed growth and nodulation enhancements were not directly investigated in this trial; endogenous hormone concentrations, polar auxin transport rates, and strigolactone signaling components were not quantified. The authors concluded that while pre-sowing seed priming with 5 to 10 µM (-)-epi-GR24 presents a promising hormone-based approach to enhance urd bean productivity and soil health, detailed gene expression analyses and hormone profiling will be essential to fully elucidate the underlying molecular pathways.
Subject of Research: Agronomic effects of synthetic strigolactone seed priming on Vigna mungo growth and soil health
Article Title: Seed priming effect of (-)-epi-GR24 strigolactone for improvement of plant growth and soil health in Vigna mungo (urd bean)
Article References: Tyagi, A., Jagwan, A., Verma, G., Chauhan, A., Chugh, P., Rani, A., & Mitra, D. (2026). Seed priming effect of (-)-epi-GR24 strigolactone for improvement of plant growth and soil health in Vigna mungo (urd bean). Discover Plants. https://doi.org/10.1007/s44372-026-01036-7
Image Credits: AI Generated
DOI: 10.1007/s44372-026-01036-7
Keywords: Vigna mungo, urd bean, strigolactones, (-)-epi-GR24, seed priming, nodulation, rhizosphere, soil dehydrogenase activity, seed yield, biological yield, plant population, PU 31 cultivar, Graphic Era Hill University, randomized block design, soil microbial population, available phosphorus, available nitrogen
News Source: Drew Townsend. (November 12, 2026). Intermediate Strigolactone Priming Boosts Urd Bean Yield and Soil Biological Activity. Scienmag.
