Objective  Applicability of a seed-coating Bacillus subtilis suspension for promoting chili pepper seedling growth was investigated.

  Method  The chili pepper, Yangjiao No. 2, was used in the study by applying a B. subtilis agent on the seeds at the pharmacopoeia ratios of suspension to seeds at 1∶2, 1∶4, 1∶6, 1∶8, 1∶10, or 1∶12 (ml∶g). Subsequently, the seed germination as well as the seedling growth and physiological characteristics were monitored to determine the effects brought about by the coating treatments.

  Result   Compared with control, the coating increased the seed germination rate and the plant height, stem diameter, leaf area, plant dry weight, and growth index of the seedlings. The effects peaked at the suspension to seeds ratio at 1∶8. The coating treatments enhanced the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) but reduced the intercellular CO₂ concentration (Ci) on the leaves resulting in an uplifted photosynthetic capacity of the plants. Moreover, the treatments decreased the MDA content and O₂⁻production rate, while increased the SOD, POD and CAT activities, of the leaves that were conducive to sustaining high contents of chlorophyll and soluble protein for the plants. The seedling growth index was found positively correlated with the net photosynthetic rate, transpiration rate, and stomatal conductance but inversely correlated with the intercellular CO₂ concentration.

  Conclusion  The seed-coating B. subtilis suspension alleviated the peroxidation of membrane lipids and increased antioxidant enzyme activities with a sustained high photosynthetic capacity in the leaves benefiting a vigorous subsequent growth of the seedlings. The pharmacopoeia ratio at 1ml of suspension to 8g of seeds provided the most desirable results.