Untitled - International Rice Research Institute

Seedborne fungi causing foliage diseases in rice
Alternaria padwickii (Ganguly) Ellis
syn. Trichoconis padwickii Ganguly
Trichoconiella padwickii (Ganguly) Jain
Disease caused: stackburn
a. Symptoms
On leaves—large oval or circular spots with a
pale brown center and distinct dark brown margin.
Color of center eventually becomes white and
bears minute black dots.
On grains—pale brown to whitish spots with black
dots at the center and dark brown border.
Roots and coleoptile of germinating seedlings—
dark brown to black spots that eventually coalesce.
Small, discrete, and black bodies are
formed on the surface of the darkened area as
decay proceeds.
b. Occurrence/distribution
Stackburn disease is widespread in most of the
rice-growing countries worldwide (Fig. 4).
c. Disease history
The disease was first reported in the U.S. It resembles
black rust of wheat on rice leaves, but
only sclerotia and mycelium were observed.
Later the fungus was observed in and on rice
seeds.
d. Importance in crop production
Stackburn leaf spot disease is not considered to
be of economic importance. However, seed infection
results in grain discoloration, which may
reduce germination and lower grain quality. The
disease potential of stackburn is very low and the
yield loss caused by A. padwickii in literature
may be overestimated. The effect of infected
seed on seed germination is not yet properly assessed.
Detection on seed
a. Incubation period on blotter
A. padwickii is easily observed on seeds using the
blotter method 5 d after seeding on moistened
blotter and incubated under NUV at 21 °C. The
detection frequency is about 67.1% on seeds
coming from different regions (Fig. 5a,b).
b. Habit character
Seed infected with A. padwickii after incubation
shows abundant aerial mycelia, hairy to cottony,
profusely branched, grayish or hyaline when
Fig. 4. Occurence of stackburn (Ou 1985, Agarwal and Mathur 1988, EPPO 1997).
14