Abstract: By the methods of water culture and soil culture, this paper studied the threshold values of cobalt (Co) toxicity to vegetables. Water culture was performed to select the most Co-sensitive vegetables from the 18 vegetable species commonly cultivated in Fujian Province, and soil culture was conducted to determine thethreshold values of soil Co toxicity to the selected vegetable species. Under water culture, low concentration (0.01 and 0.1 mg·L^-1) Co stimulated vegetable growth, while high concentration Co had toxic effects. Based on the apparent symptoms and the EC₂₀ values (effective concentration causing a 20% decrease of shootbiomass), Chinese cabbage (Brassica pekinensis) and cucumber (Cucumis sativus) were the most sensitive vegetables. In the followed soil culture with cucumber, no obvious stimulating effects of Co were observed. With the increasing concentration of added Co, the shoot biomass of cucumber decreased significantly. Based on the EC₁₀ (effective concentration causing a 10% decrease of shoot biomass) and the regression between soil DTPA-Co and total Co in the field, the threshold values of soil Co toxicity were estimated to be 2.7 mg·kg^-1 (DTPA-Co) and 98 mg·kg^-1(total Co).

Key words: Spodoptera litura, Microplitis sp., Spodoptera litura nuclear polyhedrosis virus, Virus transmission