Sorghum Diseases in India

Odvody: Heavier (clay) soils retain deposited
water for longer periods than do sandy soils and
provide a more conducive environment for attack
by pathogens.
Mushonga: Our experience in southern Africa is
that more seedling problems are noticed in
sandy soils than in heavier types, Does this differ
with your experience?
Odvody: The stand-establishment problem is a
complex syndrome, involving many interacting
factors. There could be several factors, other
than bacterial or fungal pathogens, causing
stand loss in sandy soils. One could be nematodes.
Anahosur: In India, seed rot and seedling blight
due to Fusarium spp and Curvularia spp, Rhizoctonia
spp, Aspergillus spp, etc., have been found.
Seed treatment with thiram has helped to reduce
this malady. Only when seeds are not treated,
this problem is noticed.
Odvody. I agree, except where seed has been
significantly damaged by these fungi (excluding
Rhizoctonia). The fungicide may control further
fungal attack on these seeds, but the probable
low vigor in seedlings could have increased vulnerability
to other soilborne pathogens.
King: Some field and pot experiments using
nematacides at ICRISAT's Sahelian Centre in
Niger increased seedling establishment in
groundnut and pearl millet. It was thought that
this might to some degree have been due to reduction
in populations of parasitic nematodes.
Mughogho: There is some information on seedling
diseases of sorghum in other countries, such
as India and Nigeria, in addition to the information
provided by Odvody on the work done in
Texas.
Odvody: My report does include work done in
areas other than Texas. Many reports were not
included because they simply corroborated existing
information or they were discounted because
they failed to adequately establish associations
with seedling disease in the field. A few
reports could have been missed if they appeared
in journals that are hard to access.
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Mughogho: You have talked only about soilborne
seedling diseases. What is the role of
seedborne pathogens in seed rots and seedling
blights/diseases?
Odvody: I have talked about seedborne pathogens.
The grain mold fungi (Fusarium monoliforme
and Curvularia lunata) are active as
pathogens in seed. They cause direct damage, as
when that seed is sown, can cause seed rots,
blighting, and seedling disease. Colletotrichum
graminicola can be transmitted by seed, but its
association with seedling disease appears to be
limited and it is not reported as causing seed
rots. I did not mention it in my presentation, but
Watanabe's report of seedborne Glaeocercospora
sorghi causing subsequent seedling disease is the
only well-documented case for this pathogen,
although its seedborne nature is often reported.
Many papers report seedborne associations of
common sorghum pathogens and other fungi,
but their subsequent roles in seed rots and seedling
diseases are not documented. Sometimes
their role in seedling disease is evaluated in sterile
soil or through inoculation, but that does not
prove an association with seed rots and seedling
diseases in the field where soils have competitive
microflora. I do not believe that listing these
types or reports serves a constructive purpose as
we seek to delineate the active seedborne and
soilborne biotic components related to seed rots
and seedling diseases.
Laing: Are there Rhizoctonia solani groups causing
seedling establishment problems in sorghum?
Odvody: R. solani has been isolated from sorghum
seedlings, but it is not a problem. The
root-attacking R. solani isolates are of a different
anastomosis group than those attacking foliage.
Wall: In Central America, stand establishment
problems are mainly related to ants and birds,
and to some extent grain molds, but mostly to
the first two.
Starr: With regard to effects of nematicides on
stand establishment, it should be noted that
many nematicides have some fungicidal activity.
This fungicidal activity is particularly evident at
the higher rates of chemical applications used in
experimental studies.