Soil-dependent variation in strigolactone signaling distance revealed by a parasitic seed germination bioassay

Strigolactones are root-exuded plant metabolites acting as germination stimulants for several parasitic weeds. While strigolactone bioactivity in soil is assumed to be temporally and spatially restricted, quantitative estimates of their signaling distance are lacking. This study aimed to quantify strigolactone signaling distance in soils of contrasting texture, as an estimate of physical transport distance, and to assess the influence of soil biological activity and water content.

Phelipanche aegyptiaca seed germination served as a biological indicator in a soil column experiment to estimate synthetic strigolactone GR24 transport in clay, loamy sand and pure sand soils. Induced germination declined with increasing distance from the GR24 source in all soils, but at markedly different rates. Effective signaling distances, estimated using log-logistic models fitted to the data, ranged from 0.05 to 14.2 mm across soils and treatments. Signaling distance was shortest in clay soil and increased in coarser-textured soils. Soil sterilization increased signaling distances, particularly in loamy sand, indicating a strong role for microbial degradation. Higher soil water content increased the signaling distance, especially in coarse soils. In pure sand, induced germination remained high at the maximum tested distance, with no significant distance dependence in sterilized treatments.

This study provides quantitative evidence that strigolactone signaling distance in soil varies widely with soil properties. These findings demonstrate that both biotic degradation and abiotic transport constraints limit the signaling range. The bioassay introduced here offers a novel tool for evaluating strigolactone fate in soil, but requires further testing with natural strigolactones. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.