PCR-based Detection and Differentiation of Anthracnose Pathogens, Colletotrichum gloeosporioides and C. truncatum, from Vegetable Soybean in Taiwan

Anthracnose of vegetable soybean sometimes occurs in summer and causes severe symptoms and yield loss in southern Taiwan. Despite previous reports that Glomerella glycines and Colletotrichum truncatum were causal agents of soybean anthracnose, C. truncatum and C. gloeosporioides (teleomorph G. cingulata), but not G. glycines, were identified as the major pathogens causing anthracnose on the pods and stems of vegetable soybeans from 2003 to 2005. Most strains of C. truncatum and C. gloeosporioides were derived from diseased pods. Morphological formation of fruiting bodies separates the Colletotrichum isolates into two groups. Colletotrichum truncatum forms acervuli only while C. gloeosporioides produces acervuli and/or perithecia. Based on the sequence variation in the ITS1 and ITS2 regions, C. truncatum isolates were highly similar (99-100% nucleotide identity) while C. gloeosporioides isolates diverged into two separate groups that were not associated with morphotype. For early detection of C. truncatum and C. gloeosporioides infection on vegetable soybean plants, two species-specific primer pairs Colg 1/Colg 2 (expected size of 443 bp) and Colg 1/CT 2 (375 bp) were designed that allowed differentiation of C. gloeosporioides and C. truncatum in multiplex polymerase chain reaction.