Effect of amino acids from soybean root exudates on hyphal growth of pathogenic fungi of soybean root rot

Root exudates of two soybean (Glycine max L. Merr.) cultivars, Hefeng 25 (HF25) and Suinong 10 (SN10), which were susceptible and resistant to soybean root rot, respectively, and grown in quartz sand, were collected with distilled water. The effects of the root exudates on hyphal growth of pathogenic fungi, Fusarium oxysporum Schlecht.(F. ox. Schlecht.) and Fusarium solani (Mart.) Sacc.F. so. (Mart.) Sacc., were tested. The results showed that soybean root exudates from both seedling and flowering stages stimulated hyphal growth of F. ox. Schlecht. Root exudates from maturing plants stimulated the growth of F. so. (Mart.) Sacc. There were 16 amino acids detected from HF25 root exudates, while 14 from SN10 root exudates. HF25 roots exudated more types and higher total concentrations of amino acids than SN10. The major amino acids in root exudates of HF25 and SN10 were arginine and aspartic acid, respectively. Bioassay demonstrated that arginine and tyrosine significantly stimulated hyphal growth of F. ox. Schlecht., but serine and aspartic acid inhibited its growth. Aspartic acid inhibited hyphal growth of F. so. (Mart.) Sacc. These results suggested that amino acids in soybean root exudates played significant role on hyphal growth of pathogenic fungi of root rot, and the effects varied with soybean cultivars, possibly related to types and concentrations of amino acids in their root exudates, as well as species of pathogenic fungi.