Abstract: Biotic and abiotic elicitors have dramatically promoted the accumulation of secondary metabolites in plant cell cultures. In this paper , through the orthogonal design and the randomized complete experimental design, we have investigated effects of nitrate source and fungal elicitors on growth and polysaccharide accumulation in suspension cultured protocorms of Dendrobium candidum. It has been found that nitrate (KNO₃) promoted propagation of D. candidum protocorms in suspension culture, fresh weight and dry weight of protocorms increased significantly ( P < 0.05). However, ammonium ( (NH₄ )₂ SO₄ ) only stimulated significant increase of fresh weight of protocorms ( P <0. 05), nitrate and ammonium were not interrelated for biomass of protocorms. The results demonstrate that 67-V medium supplemented with (NH₄ )₂ SO₄ 100mg/L, KNO₃ 800mg/L, sucrose 30g/L and potato extract 200 g/L was best for the growth of protocorms. In addition, fourteen fungal elicitors did not significantly influence biomass of suspension cultured protocorms of D. candidum ( P > 0.05). However, compared with the content of polysaccharides in the control, the one in the protocorms of D. candidum elicited by fungi g6, g14, g5 and g4 raised 14%, 9%, 6% and 4% , respectively. Since D. candidum is a rare medicinal plant and polysaccharides are important active components in the plant, our results show good application prospect for producing protocorms of D. candidum in suspension culture.

Key words: Orthogonal design