Sorghum Diseases in India

term, proposed by Glueck et al. (1977), is my
preference as the descriptor of this complex
syndrome.
Field tolerance to grain deterioration has
been achieved in commercial brown-grained
sorghum cultivars. This characteristic is determined
by the presence of a testa and by high
tannin content (see Waniska, this volume). In
areas where environment has not favored panicle
fungal colonization, sorghum hybrids having
low tannin content normally produce high
yields and find good acceptance by consumers.
High-tannin sorghums comprise about 85%
of Argentina's sorghum production. Coordinated
efforts of breeders and pathologists have
developed new screening procedures that identify
good sources of stable resistance to grain
molding in low-tannin sorghums.
Head blight
Recent reports of severe incidence of head blight
in central Argentina are of considerable concern
because this disease had not been reported from
this area, and panicle damage was serious.
Sorghum downy mildew (SDM)
Most Argentine commercial hybrids are resistant
to downy mildew caused by Peronosclerospora
sorghi (Weston and Uppal) Shaw. In 1985/86
a change in the pathogen population was detected
in some areas of Chaco and Cordoba provinces.
Commercial hybrids having RTx 430 or
derivatives as male parents were susceptible,
showing systemic and local symptoms.
Sorghum breeders have used RTx 430 as a
source of sorghum downy mildew (SDM) resistance
since the 1970s, developing hybrids with
high levels of resistance.
The change in the SDM pathogen populations
represents the major threat to sorghum
production in these provinces even though
many other conditions must be present for an
epidemic to occur. A widespread and uniformly
susceptible genotype, environmental conditions
favoring reproduction of the new race, and time
for disease build-up are required. Several reports
(Craig and Frederiksen 1980; Pawar et al.
1985) clearly demonstrate variations in Peronosclerospora
sorghi virulence. There is evidence
that suggests that unknown factors have prevented
new races from reaching their full potential,
like the case of pathotype 3 in the United
States of America.
Action to prevent a drastic SDM epidemic
includes identification of the new race, and detection
of sources of resistance. These objectives
have been achieved.
Bacterial Diseases
During the last 5 years, a significant build-up of
bacterial diseases has occurred in Argentina.
Three aspects related with these microorganisms—leaf
symptoms, grain infection, and
stalk rot—occupy our attention.
Leaf symptoms
Bacterial stripe (Pseudomonas andropogonis) is
now common in almost every sorghum crop.
Usually, bacterial streak (Xanthomonas holcicola)
is also seen, but to a lesser extent. Since 1983/84,
severe bacterial leaf damage has been recorded
in our breeding nursery at Pergamino, Buenos
Aires Province. Some genotypes showed symptoms
before flowering, rather than after bloom
as expected. Something has changed. We don't
know if we are dealing with a pathogen population
that comprises virulent strains causing
severe sorghum infection. Avezdzhanova and
Sidorova (1978, pp. 63-65) compared pathogenicity
of different strains of bacterial leaf spot
and bacterial streak affecting sorghum.
Likewise we don't know much about time of
initial infection, predisposing factors, effects on
yield or grain quality, or if a vector is involved.
Grain infection. In 1984/85, a sorghum germination
problem caused by Pseudomonas spp
was identified. Large numbers of bacteria were
observed in close proximity to the embryos, and
black and brown lesions were seen in every case.
Infected seeds emerged as poor seedlings and
decayed easily.
Gaudet and Kokko (1986) mentioned a seedling
disease of sorghum caused by seedborne
Pseudomonas syringae.
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