Sorghum Diseases in India

Figure 2. Scanning electron micrograph of a spore ball of Tolyposporium ehrenbergii. Most
of the peripheral spores have fallen away.
ficially contaminated seed have failed to reproduce
symptoms. Similarly, inoculations of
plants at juvenile stages of growth did not develop
smut. The only method that permits infection
is when plants are inoculated at the
boot stage before the ear emerges. Infection occurs
when the inflorescence is still enclosed in
the boot or about the time it emerges when the
flowers are very young. Manzo (1976) wrote
that floral infection by T. ehrenbergii takes place
when inoculation is done at boot stage, with
decreasing infection from preanthesis to early
anthesis, and infection does not occur during
early seed filling. In this respect the mode of
infection of T. ehrenbergii is identical to that of
T. penicillariae, the long smut of millet (Bhatt
1946).
We propose that the annual recurrence of the
disease is from spore balls picked up from the
soil surface by winds during a dry period, deposited
in the flag leaf, then they are washed
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down in the flag leaf where conditions are conducive
for sporidia production and penetration
(Fig. 3). This accounts for the occurrence of infected
heads under bags. Frequently, perhaps
because of the higher humidity, infection is
higher under a bagged head than an uncovered
head. Bagged sterile heads also develop long
smut. Freshly produced spores are again wind
blown and could serve as inoculum within the
same location. Consequently, experiment station
nurseries with several dates of sowing or flowering
are more likely, in some seasons, to have
high levels of long smut.
The fungus penetrates the developing ovary,
mostly through the style (rarely through the
ovary wall), and rapidly colonizes the internal
tissues. Ramification of the invading hyphae is
soon followed by the aggregation of spore balls
that progress from the upper part of the young
sorus. In about 15 days, following inoculation,
symptoms of the disease should appear.