Biological indices of runner bean (Phaseolus coccineus) seeds to priming and drying with cucurbitacin phytonematicides 

Abstract

Phytonematicide priming methods often give uneven results, mainly due to variability in how seeds respond to allelochemicals. The movement and effect of cucurbitacin-rich priming solutions inside seed embryos, especially with different emergence patterns, are still not clearly understood. Therefore, it is necessary to evaluate the biological sensitivity and safe stimulatory concentrations for runner bean seeds primed using PAD technology with cucurbitacin-based phytonematicides. This study investigated the biological indices of runner bean (Phaseolus coccineus) seeds ten days after priming in cucurbitacin-based phytonematicide solutions during 2024 at the University of Limpopo, South Africa. Runner bean seeds were primed in geometric series concentrations (0–64%) of Nemarioc-AL (containing cucurbitacin A) and Nemafric-BL (containing cucurbitacin B) for six hours, dried at 25°C, and germinated inside a temperature-controlled growth chamber. Data on germination percentage, radicle length, plumule height, and plumule diameter were analysed using the Curve-fitting Allelochemical Response Dose (CARD) algorithm to generate biological indices, allowing the computation of midpoint stimulation concentration. Positive quadratic relationships were observed between increasing phytonematicide concentrations and most germination variables, with R² values ranging from 89% to 99%. Negative quadratic relationships were not included in the in biological indices. The calculated overall sensitivity indices were 39 for Nemarioc-AL and 14 for Nemafric-BL, indicating high tolerance of runner bean seeds to both products. The respective MPC values were 1.05% and 0.58%, which supported 100% germination during validation tests. These findings demonstrate the potential of PAD technology for integrating phytonematicides into seed-based nematode management strategies without inducing phytotoxicity, particularly for crops exhibiting hypogenous emergence. In conclusion, the findings confirm that seeds with hypogenous emergence can serve as effective carriers of cucurbitacin phytonematicides,