First Report of Southern Blight of Silvery Messerschmidia Seedlings in Taiwan

Silvery messerschmidia, Messerschmidia argentea (L.) Johnston, of the
Boraginaceae, is indigenous to Taiwan and grown as an ornamental, for
windbreaks, or as a shade tree. During the summer of 2005, a sudden wilt
of 1-year-old plants was observed in a nursery in central Taiwan. Initial
symptoms included stem necrosis at the collar, leaf yellowing, and tan
discoloration of leaves. As stem necrosis progressed, infected plants
wilted, defoliated, and died. Necrotic tissues were covered with whitish
mycelium with clamp connections that formed reddish brown spherical (1
to 2.2 mm in diameter) sclerotia. A fungus was consistently recovered
from the interface of diseased and healthy stem tissue, disinfested for 1
min in 0.5% NaOCl, and plated on Difco (Sparks, MD) potato dextrose
agar (PDA) amended with 100 ppm of ampicillin. Pure cultures were
prepared by transferring single hyphal tips to PDA, and Sclerotium rolfsii
(Sacc.) was identified (1). Pathogenicity of two S. rolfsii isolates was
confirmed by inoculating 3-month-old silvery messerschmidia seedlings
grown in pots. Inoculum consisted of a single agar disk of a 7-day-old
culture used per pot or a single sclerotium produced in 10 days on PDA
and added per pot. Both the mycelium on the 0.5-cm-diameter agar plug
and the sclerotium touched the base of the plant stem. Four plants were
inoculated with mycelia, four with sclerotia, and four were noninoculated
controls. All plants were kept in a growth chamber at 25 to 35°C with
relative humidity of more than 95%. Initially, the basal stems were
covered by whitish mycelia growth with a fanlike pattern from the
inoculum, and brown, water-soaked necrotic lesions developed near the
soil line. Inoculated plants developed symptoms within 4 days, wilted
gradually in 7 days, and all were eventually killed in 11 days. Plants
inoculated with sclerotia developed disease at a slower rate and control
plants remained symptomless. Sclerotia developed on diseased tissues
and S. rolfsii was reisolated. This disease has been observed on many
species of plants (2), but to our knowledge, this is the first report of
southern blight of silvery messerschmidia seedlings caused by S. rolfsii in Taiwan