Sorghum Diseases in India

lated to seed-health requirements for seeds
grown for domestic use.
Epidemiological data available for the majority
of seedborne microorganisms is insufficient to assign
the microorganism to any of the above classes.
Seedborne Diseases of Sorghum
Approximately 40 microorganisms are listed as
seedborne on sorghum (Sorghum bicolor L.)
(Richardson 1979). These represent more than
75% of all sorghum diseases. Existing information
on the seedborne phase of economically important
sorghum diseases with respect to the
above considerations is reviewed.
Infected seeds as the main inoculum source
Ergot, caused by Sphacelia sorghi, occurs in Africa
and Asia. The disease affects individual florets,
causing poor grain development. It is
associated with sterility and can cause problem
in hybrid seed production where male-sterile
lines are used as female parents (Futtrell and
Webster 1965). Sclerotia mixed with the seeds
are considered as an important source of primary
inoculum for the new crop. Ergot has been
added to this group only on the basis of morphology
and not as the basis of scientific evidence.
It may be important to sow seed free of
sclerotia. Sclerotia can be separated from seed
by immersing seeds in a salt solution.
Covered kernel smut (Sporisorium sorghi) affects
floral parts, and individual seeds are replaced
by sori. Seeds contaminated by teliospores
released from infected plant parts are the
main inoculum source. The disease is effectively
controlled by seed treatment. If seed treatment is
not applied, major losses can result.
Loose kernel smut (Sphacelotheca cruenta) also
attacks the panicle. Spores become attached to
seeds during maturation and harvest, and then become
the primary inoculum source. Control can be
achieved with seed treatment (Hansing 1957).
Infected seeds as a minor inoculum source
Head smut (Sporisorium reilianum) is of great economic
importance, particularly in USA. All or
part of the panicle is destroyed. Disease incidence
298
is directly related to the number of spores of
S. reilianum present in the soil; these infect young
seedlings, grow systemically throughout the
plant, then produce typical symptoms at flowering
time. Spores released from infected floral
parts fall to the soil; they survive for as long as 2
years (Saf'yanov et al. 1980). The pathogen also is
seedborne, but as such is not an important inoculum
source (Frowd 1980). Dalassus (1964) found
that inoculation of seeds had no effect on disease
incidence. Some degree of control can be
achieved with cultivar resistance. Chemical seed
treatment does not seem to be particularly effective,
although one report indicated success with
benomyl (Popov and Silaev 1978).
Long smut (Tolyposporium ehrenbergii) occurs
in African and Asian nations. It is typified by
long, curvular sacs scattered through the heads.
Spore balls, consisting of masses of teliospores
on the soil surface, are the main inoculum
source. Contaminated seeds also can be a source.
Hafiz (1958) showed that diseased heads developed
on 10-20% of the plants grown from seeds
coated with spores. Disease incidence was
higher, however, when healthy seeds were
grown in infested soil.
Sorghum downy mildew (Peronosclerospora
sorghi) is a serious disease of maize and sorghum
in many parts of the world, causing stunting and
chlorosis. Thick-walled oospores are produced in
systemically infected plants. These infest soil and
become a major inoculum source. Bain and Alford
(1969) detected fungal mycelium in the embryo
of seeds. It has been consistently shown,
however, that the pathogen does not survive in
seed dried below 20% moisture, and there is little
evidence that mycelium in dry seeds is transmitted
to plants (Frederiksen 1980). Nonattached oospores
could, however, be an inoculum source in
seedlots. Kaveriappa and Safeeulla (1978) showed
that transmission can occur when seeds are contaminated
by glumes carrying oospores. In Texas,
phytosanitary certificates are issued, after field inspection
for the disease, to ensure that oosporeinfested
seeds do not occur (Frederiksen 1980).
Seed treatment with metalaxyl has proved to be
an effective control (Frederiksen 1980). Integrated
control practices, combining chemical treatment
with cultural practices, also have been investigated
(Odvody et al. 1983). Resistant hybrids controlled
the disease well in Texas in the 1970s, but
new races appeared in 1979-80 (Odvody et al.
1983). The propensity for the development of new