Sorghum Diseases in India

Principles and Criteria of Seed
Transmission of Sorghum Pathogens
D.C. McGee 1
Abstract
More than 40 microorganisms are listed as seedborne on sorghum. This review categorizes them
according to the criteria of transmissibility to the new crop and/or effects on seed quality. The main
inoculum source is seed-transmitted in only three diseases. Several other important diseases are
seed-transmitted, but with these crop residues are usually a more important inoculum source.
Grain molds occurring in the seed-production field cause serious losses in seed viability. Fusarium
spp and Curvularia spp are the major causal agents. Many seedborne microorganisms have been
identified that do not cause sorghum disease just because of their presence on the seeds. Nonseedbome
pathogens are of concern in sorghum-seed production in respect to adverse effects on yield
and stand establishment.
Introduction
More than 40 microorganisms are listed as seedborne
on sorghum. This review categorizes
them according to the criteria of transmission to
the new crop and/or effects on seed growth. The
main inoculum source is seed-transmitted in
only three sorghum diseases. Several other important
diseases are seed-transmitted, but with
these pathogens, residues are usually the more
important inoculum source. Grain molds occurring
in seed-production fields cause serious
losses in seed viability.
Criteria for Determining Importance
of Seedborne Pathogens
The annotated list of seedborne diseases records
more than 1500 microorganisms as being seedborne
on 600 genera of plants (Richardson 1979).
To obtain a perspective of the large numbers of
seedborne microorganisms, McGee (1981) described
four classes into which they might be
assigned. The first comprises seed-transmitted
pathogens and the infected seeds become major
inoculum sources. The second class contains
pathogens that are seed-transmitted, but infected
seeds are relatively insignificant as sources
of inoculum. The third and largest class lists
those microorganisms never before known to
cause disease as a result of their presence on
seeds. In the fourth class are those pathogens
that attack new seeds during formation or in
storage, thus affecting the seed's appearance,
germination, and/or vigor.
Another consideration in assessing the
importance of seedborne microorganisms is
whether the seed is grown for sowing in the
country where it's produced, or for export to
another country. When grown for domestic use,
control measures are needed only for important
pathogens in the first or fourth classes described
above. On the other hand, seed grown for export
requires control measures so that it can meet the
seed-health testing dictated by the plant quarantine
regulations of the country of destination.
Plant quarantine requirements are often unre-
1. Seed Pathologist Department of Plant Pathology, Seed Science Center, Iowa State University, Ames, IA 50011, USA.
McGee, D.C. 1992. Principles and criteria of seed transmission of sorghum pathogens. Pages 297-302 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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