First report of leaf blight on Calathea picturata caused by Exserohilum rostratum in Taiwan.

Many Calathea species in the family Marantaceae are beautiful ornamental plants with variegated foliage. Among them, C. picturata ‘Argentea’, an evergreen perennial that has pale green leaves with dark green margins and a red underside, is a popular houseplant in Taiwan. In 2004, a new foliage disease that caused leaf blight of C. picturata ‘Argentea’ was first observed in a nursery in southern Taiwan. Initial symptoms were tiny, brown spots that appeared on the leaves of all ages, which quickly enlarged and coalesced. These necrotic lesions spread to cover the entire leaves in high temperature and moisture conditions and caused leaves to shrivel and eventually die. A dematiaceous hyphomycete with multicelled conidia was consistently isolated from the diseased leaves after being surfaced sterilized with 10% Clorox and placed on vegetable juice agar (10% V8 juice, 0.02% CaCO3, and 2% agar [VJA]). Pathogenicity of the isolate was tested by spraying ‘Argentea’ calathea leaves with a conidia suspension (1.6 ×...