Sorghum Diseases in India

aces has increased concern about transmission
by infected seed.
Sooty stripe (Ramulispora sorghi) is common
under warm, humid conditions in some countries.
The pathogen survives as sclerotia. Seed
infection has been detected (Lele et al. 1966), but
proof of transmission is lacking.
Target leaf spot (Bipolaris sorghicola) survives
on debris or on alternate hosts. It has been isolated
from seeds (Purss 1953).
Charcoal rot (Macrophomina phaseolina) is a
major disease in drier regions. It is reported as
seedborne, but soilborne sclerotia are the major
inoculum sources. One report (Chumaevskaya
1962) recommended seed treatment.
Milo disease (Periconia circinata), occurs in USA,
causing a root and crown rot in some genotypes.
Crop residues and soil are well recognized as the
major inoculum sources, and it has been isolated
from seeds (Hansing and Hartley 1962).
Zonate leaf spot (Gloeocercospora sorghi) commonly
occurs during wet periods. It is seedborne
(Bain 1950). Ciccarone (1949) suggested
that zonate leaf spot was introduced into Venezuela
by infected seeds. Sclerotia overwintering
in dead leaf tissues provide inoculum for the
following season's crop (Girard 1978).
Fusarium root and stalk rot (Fusarium moniliforme)
is a common disease in tropical and
temperate regions. Locally, losses may approach
100%. Infected debris is the main inoculum
source. Seed can be a minor source (Mathur et
al. 1967). Control can best be achieved by sowing
hybrids with good stalk strength and then managing
so as to avoid or reduce stress.
Bacterial leaf spot (Pseudomonas syringae pv
syringae) has been reported from most countries.
The pathogen survives on crop residues, and
can survive for as long as 3 years in dry sorghum
seeds. Sundaram (1980) indicated that
sowings with seed from diseased plants, growing
in sterile soil, developed the disease.
Other bacterial pathogens of sorghum recorded
as being seedborne are Pseudomonas
andropogonis, Xanthomonas holcicola, and X. rubrisorghi
(Easwaran 1967; Sundaram 1980).
Nonpathogenic seedborne microorganisms
Many studies of the seed microflora of sorghum
have been reported, usually as lists of microorganisms
detected in seed-health tests. Many of
these microorganisms are pathogens, such as
Fusarium spp and Curvularia spp, but pathogenic
activity for the majority has not been established.
Papers by Mathur et al. (1975), Hansing
and Hartley (1962), Pinheiro and Neto (1979),
Rani et al. (1978), Tarr (1962), and Williams and
Rao (1981) reflect the range of genera found in
different parts of the world.
Pathogens affecting seed quality
The exposed nature of sorghum seeds render
them susceptible to invasion by parasitic microorganisms
and to effects of weathering in the
production field (Frederiksen et al. 1982). Moldy
seed shows as pink or blackened seed scattered
through the head. Dead embryos are characteristic
of the condition (Williams and Rao 1981).
Wet weather during the 1966 harvest caused extensive
losses from grain mold and weathering
in Texas (Matocha et al. 1977). Three diseases,
grain mold, small seed, and head blight, are all
associated with reduced seed and grain quality.
The fungus Fusarium moniliforme is implicated in
each of these.
Grain mold is the result of infection of spikelets,
perhaps as early as anthesis, by F. moniliforme
and Curvularia lunata. The pathway of
infection of the seed by F. moniliforme has been
elucidated by Castor (1981). This work distinguished
primary pathogenic effects from secondary
effects associated with field weathering.
In the latter case, fungi colonize mature grain
(Castor 1981). There is value in these distinctions;
they are important in screening sorghum
lines for resistance to infection by F. moniliforme.
Lines that consistently develop less grain mold
have been identified (Frederiksen et al 1982).
"Small seed" occurs, to some extent, in sorghum
each year. Castor (1981) showed that infection
at anthesis by F. moniliforme or C. lunata
causes formation of a false black layer, resulting
in light grain. Inoculation with F. moniliforme
induced "small seed.''
Head blight, caused by F. moniliforme, differs
from grain mold in that it is the result of infection
of the panicle, rachis branches, or peduncle.
Grain mold, on the other hand, is a result of
spikelet infection. Major losses were caused by
head blight in southern Texas in 1979 (Castor
and Frederiksen 1980). Sorghum genotypes differ
in their response to this disease.
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