Cell wall degrading enzymes of Colletotrichum lindemuthianum: their role in the development of bean anthracnose

Abstract

Colletotrichum lindemuthianum race γ secreted into the media endo-polygalacturonase (isoelectric point [pI] 9·4), α-arabinofuranosidase (pI 3·6), gb-galactopyranosidase (pI 4·0), α-galactopyranosidase (pI 3·8), and protease (pI 9·9)—each in a single identifiable form when grown in culture with sodium polypectate or isolated Phaseolus vulgaris hypocotyl cell walls as the main source of carbon. Two forms of pectin lyase with isoelectric points of 8·2 (PL I) and 9·7 (PL II) were also present in both media. Another form of protease (pI 6·9) was present exclusively in the mycelial extract. The molecular weights of all these enzymes were determined. Lesions on hypocotyls of P. vulgaris produced following inoculation with C. lindemuthianum contained the following fungal enzymes: pectin lyase II, α-arabinofuranosidase, α-galactopyranosidase, β-galactopyranosidase and protease (pI 9·9). Polygalacturonase activity was not detected. A proteinaceous inhibitor of polygalacturonase was present in both infected and uninfected tissue. Pectin lyase activity was first detected in infected hypocotyl tissue on the 4th day after inoculation and increased rapidly from day 6 onwards. This increase was associated with greater fungal growth, an increase in pH of the hypocotyl sap, and the appearance and expansion of lesions.