The Influence of Clopyralid in Soil on Leaf Morphology of Pisum sativum L. and Its Relationship with Shoot Clopyralid Concentrations

The relationship between leaf symptoms caused by clopyralid and shoot concentrations of clopyralid was investigated by cultivating Pisum sativum L. At 1–10 μg/kg-dry weight (DW) of clopyralid in soil, the clopyralid concentrations in shoots increased up to 14 days and then decreased by 28 days after sowing. The fifth seedling leaf, which expressed the most serious symptoms, developed during the period when the shoot concentrations of clopyralid were at their highest and the symptoms in leaves formed after the fifth leaf became slightly less pronounced as the shoot clopyralid concentrations decreased. Thus, the severity of leaf symptoms depended on the shoot clopyralid concentration. The EC50 and EC10 values of clopyralid for P. sativum were calculated from the dose–response curve using an injury index based on the degree of leaf symptoms. The EC50 value was 30.9 μg/kg-DW (95% CI 28.4–33.4 μg/kg-DW), and the EC10 value was 3.2 μg/kg-DW (95% CI 2.2–4.1 μg/kg-DW), respectively. In addition, the dose–response curve obtained using the injury index increased from 1 μg/kg-DW of clopyralid in soil, confirming that the injury index could be used to estimate soil concentrations within a range that causes physiological disorders.