Sorghum Diseases in India

of soil Typical symptoms of L. africanus on sorghum
included swollen and distorted roots.
Management Alternatives
Management of nematode populations to reduce
crop losses in sorghum production systems
may be difficult. Dramatic yield responses to
nematicide treatments have been observed, but
it is not likely that a chemical approach will ever
be a practical or economically viable option for
sorghum. Biological control of nematode populations
does occur in nature (Kerry 1981), but the
ability to manipulate such systems to practical
degree is not likely for some time. Host resistance
and cultural control, on the other hand,
holds promise for alleviating damage by nematode
pathogens to sorghum.
Resistance to the highly specialized sedentary
endoparasites is likely to be relatively easy
to identify; numerous crop species are known to
contain sources of resistance to Meloidogyne, Heterodera,
and Rotylenchulus species (Anonymous
1978). Resistance to the less specialized migratory
ectoparasites will be more difficult to identify
and may be more difficult to manipulate in
traditional plant breeding programs. However,
as indicated previously, the data available indicate
that some variability for reaction to different
nematode species does exist within the
sorghum germplasm pool. Recent successes in
identifying resistance to similarly nonspecific
fungal pathogens and arthropod pests (Harris
1980) suggest that similar success awaits us with
regard to nematodes if appropriate effort is put
forth.
Crop rotation as a cultural control system can
help alleviate nematode damage to sorghum.
Successful and practical rotations require
knowledge of nematode population dynamics
on ail crops in the rotation and works best if a
single nematode species predominates. In some
instances crop rotation can significantly reduce
the impact of nematodes on crop productivity
while in other instances the rotation may simply
serve to maintain diversity in the ecosystem and
perhaps avoid major problems that frequently
accompany monoculture systems. Development
of effective rotational systems is difficult due to
the constraints of the environment, cultural biases,
and availability of suitable alternate crops.
Because nematode damage is often related to
plant stresses from other sources, minimization
of these stresses will help reduce nematode
damage. Improvements in soil fertility and reduction
of water stress will enable sorghum to
escape some nematode damage. Cultural practices
to increase the organic content of soils are
beneficial in that they can lessen the impact of
nematodes.
Conclusion
These few reports provide ample evidence of
many nematode species parasitic and pathogenic
on sorghum. Additional species are likely
to be identified with further study. The Heterodera
and Rotylenchulus species now recognized
as parasitic on sorghum will undoubtedly prove
to be pathogenic in view of the aggressiveness of
members of these genera on other plant species.
Because most nematode-related crop productivity
problems lack diagnostic symptoms and
the pest itself is not readily visible, nematodes
are frequently an overlooked component of the
pest complex attacking a particular crop. Although
nematodes may not be a problem in
every field in which crops are grown, their frequency
distribution is sufficient to make nematodes,
as a group, pests of significant impact for
nearly all crop species.
At present there is a critical need to examine
the parasitism of sorghum by numerous species
of nematodes associated with sorghum in field
surveys. The relative pathogenicity of these species
must also be determined. Determination of
the relationship between nematode populations
and sorghum yield potentials under field conditions
and the importance of particular nematode
species relative to other pest groups that limit
sorghum yields is of high priority.
In summary, plant-parasitic nematodes are
suppressing sorghum yield potentials and probably
to a greater degree than is currently recognized.
Additional efforts are needed to identify
the truly important nematode pathogens of sorghum
and to document their impact on sorghum
yields. Lastly, reduction of nematoderelated
yield losses will probably best be
achieved by development of resistant or tolerant
sorghum cultivars, by crop rotations, and by cultural
practices which eliminate other stress
factors.
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