CARPROPAMID, AN ANTI-RICE BLAST FUNGICIDE, INHIBITS SCYTALONE DEHYDRATASE ACTIVITY AND APPRESSORIAL PENETRATION IN COLLETOTRICHUM-LAGENARIUM

Biosynthesis of melanin by Colletotrichum lagenarium is essential for appressorial penetration of its host plants. Carpropamid is a novel me lanin-inhibiting fungicide for control of rice blast caused by Magnapo rthe grisea. In C. lagenarium, appressorial and colonial melanization were inhibited by carpropamid. Accumulation of melanin intermediates, scytalone, was also shown in the culture medium containing carpropamid . One of the enzymes involved in the melanin biosynthesis, scytalone d ehydratase catalyzes the conversion of scytalone to 1,3,8-trihydroxyna phthalene. We previously cloned SCD1 gene coding for scytalone dehydra tase of C. lagenarium. In this study, a recombinant SCD1 expression ve ctor was constructed using pMAL system and the recombinant scytalone d ehydratase was purified from transformed Escherichia coli. Recombinant SCD1 showed scytalone dehydratase activity in an in vitro reaction us ing scytalone as substrate. The activity was assayed by measuring the production of 1,3,8-trihydroxynaphthalene or disappearance of scytalon e, which was detectable by reverse-phase high-pressure liquid chromato graphy. Dehydration of scytalone to 1,3,8-trihydroxynaphthalene was in hibited by carpropamid in the in vitro reaction. (C) 1997 Academic Pre ss.