Sorghum Diseases in India

Biotic and Abiotic Factors Associated
with Seedling Diseases of Sorghum
G.N. Odvody 1
Abstract
Soil moisture and temperature exert major influences on seed germination and growth and on
biotic and abiotic factors affecting seedling emergence and establishment. The affected factors
include soil microflora, arthropods, nematodes, other fauna, and physical and chemical soil components.
Seed rots, seedling diseases, and the soil environment can interact to cause retarded germination,
low seedling vigor, stunting, seedling blights, and seedling death. Seedborne fungi,
including storage molds (Aspergillus and Penicillium spp), Rhizopus spp, grain mold fungi
(Fusarium moniliforme, F. semitectum, and Curvularia lunata), and foliar pathogens (Colletotrichum
graminicola and Gloeocercospora sorghi) may rot unprotected seed in cold wet
soils. Seedborne and soilborne Fusarium and Penicillium spp are reported to sometimes cause
seedling blights. Soilborne Pythium arrhenomanes and P. graminicola are the primary causes of
pre- and postemergent damping-off and seedling blight of sorghum in cold wet soil. Seed treatments
with standard contact fungicides (captan or thiram) control seed rot fungi, but not Pythium
spp New systemic fungicides (metalaxyl) and resistant germplasm may provide protection
against Pythium seedling diseases. Cropping practices and resistant germplasm may be used to
minimize seed damage caused by grain mold and weathering fungi.
Introduction
Germinating seeds, emerging, and emerged seedlings
of grain sorghum are exposed to widely
variable soil environments and soil microflora in
the diverse areas of the world where sorghum is
grown. Of the multitude of soil environmental
factors that interact and affect the establishment
of sorghum seedlings, temperature and moisture
are considered to be the major physical factors.
They directly affect the growth processes of sorghum
seedlings, and also may affect and interact
in a major way with other factors influencing sorghum-seedling
emergence and establishment—
namely soil physics and chemistry, insects, nematodes,
and soil microflora.
The soil microflora consists of many interacting
organisms, including bacteria, fungi, actinomycetes,
viruses, algae, and protozoa. The
bacteria and fungi can be strict saprophytes,
others are primarily pathogens, and another
group (the facultative parasites) are capable of
both pathogenic and saprophytic activity on sorghum
tissues. These latter two groups of organisms,
especially fungi, are the most active
against sorghum seedling tissue. Their deleterious
effect, however, is highly dependent on the
soil environment (including other soil microflora)
and susceptibility of the sorghum tissue.
The soil environment for seed germination
and growth is in constant flux; the changes in
soil microflora and physical conditions have
1. Associate Professor, Plant Pathology, Texas A&M Univeristy Research and Extension Center, Route 2, Corpus Christi; TX 78410,
USA,
Odvody, G.N. 1992. Biotic and abiotic factors associated with seedling diseases of sorghum. Pages 161-166 in Sorghum and millets
diseases: a second world review, (de Milliano, W.A.J., Frederiksen, R.A., and Bengston, G.D., eds). Patancheru, A.P. 502 324, India:
international Crops Research Institute for the Semi-Arid Tropics.
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