A manual of rice seed health testing - IRRI books - International Rice ...

Although not currently considered
a serious disease, false smut is
widely spread. Cultivation of some
varieties in hybrid rice-growing areas
with continuous cropping and
high inputs may make false smut an
endemic problem. Recently, false
smut has become a serious problem
both in hilly and foot hill regions of
Uttar Pradesh (Pathak 1990; U.S.
Singh, 1990, pers. commun).
Symptoms
Not more than four spikelets are
usually affected per panicle. Affected
spikelets are transformed into
a large yellow-green velvety mass of
spores about 1 cm in diameter or
more. Initially contained in a membrane,
the mass later bursts. The
color of the ball darkens or changes
to greenish black. If cut open, the
ball appears white in the center. The
center layer, consisting of mycelia,
has three distinguishable parts. The
innermost layer is yellowish with
mycelia and developing spores. The
middle layer is orange, with mycelia
and spores. The outer layer is green
and consists of mature spores. The
surface of the ball is covered with
powdery dark green spores.
Reports regarding the stage at
which infection occurs conflict. Infection
has been reported at booting
stage, at the early stage of flowering,
at maturity, or just before heading.
Cloudy days with high relative
humidity favor infection and disease
development during the flowering
stage.
Applying fertilizer at flowering
stage increases false smut incidence
and development. Where no fertilizer
has been applied, disease incidence
is low.
Control
Hashioka (1952) noted that spraying
fungicides a few days before heading
helps avert the disease. Copper
oxychloride effectively arrests the
disease without affecting yield
(Kannaiyan and Rao 1976).
Disease development
Both upland and lowland environments
support false smut development.
Ascospore release from the
perithecia coincides with anthesis of
early varieties of rice. Ascospores are
believed to be the source of primary
infection. Ascospores lodge on the
stigma and infect the spikelet. They
convert the ovary into a smut ball
which produces abundant conidia.
Conidia are disseminated by wind
and germinate within a few hours,
serving as the source of secondary
inoculum.
Fungal pathogens 89