Screening of Colletotrichum (Ascomycota) isolates, causal agents of Soybean Anthracnose, for Laccase production

Colletotrichum truncatum is the most common pathogen fungus associated with soybean anthracnose. Although the lignin-degrading enzyme laccase has been implicated in pathogenicity of a wide range of plant pathogenic fungi, its biological role in the Colletotrichum-soybean disease system is unknown. The extent of the infection in our country led us to examine laccase production in Argentinean Colletotrichum strains isolated from diseased soybean plants from different geographic locations. Ten strains (eight of them identified as C. truncatum), were screened for in vitro laccase production. Only six of the isolates, all of them C. truncatum, produced laccase activity when cultured on a defined medium based on pectin and asparagine as carbon and nitrogen sources, respectively. Strain BAFC 3102 (isolated from Chaco province), yielded the highest laccase titers (44 U/L) in this medium. Denaturing polyacrylamide gel electrophoresis of extracellular culture fluids revealed one band with laccase activity (mol wt 67 kDa). CuSO4 addition to media with either glucose or pectin as carbon sources increased up to 7-fold laccase production (280 U/L in the glucose medium), but the pattern of isoenzyme was not affected by culture age or medium composition. This is the first report on laccase production by C. truncatum.