Sorghum Diseases in India

drews, Sorghum and Millet Breeder, INTSOR-
MIL, and Professor of Agronomy, University of
Nebraska Lincoln, Lincoln NE 69503-0723, USA.
The major diseases of pearl millet in Zimbabwe
are ergot, smut, rust, and downy mildew.
Yields of traditional varieties growing in
farmers' fields are not affected by current disease
levels, but agriculture in many areas is becoming
more intensive, and disease pressure is
expected to increase, and resistance becomes a
factor in selecting for improved varieties and
hybrids. Top-cross hybrids and improved openpollinated
varieties appear best suited for most
areas.
Abstract:
Maize dwarf mosaic on sorghum in Kenya: some
preliminary observations
J.M. Theuri and J.G.M. Njuguna, Pathologist/
Virologist and Plant Pathologist, respectively,
Kenya National Agricultural Research Center,
Muguga, PO Box 30148, Nairobi, Kenya; N.W.
Ochanda, Alupe Agricultural Research Station,
PO Box 278, Busia, Kenya; and Vartan
Guiragossian, JP 31 SAFGRAD, PO Box 30786,
Nairobi, Kenya.
In 1987 maize dwarf mosaic was observed (24-
58% incidence) on sorghum in the Central Province
highlands and in the Rift Valley and in the
Western Provinces (0-100% incidence). Infection
was not observed in the Eastern Province. At the
Maguga Center (Central Province highlands), infected
plants showed, on average, height reduction
of 16% and head size reduction of 13%. At
Alupe (Western Province), 10 of the 25 ICRISAT
lines in sorghum trials were heavily attacked (disease
index 2.5). Ten of the 11 local varieties in the
trial showed little infection. Of the ICRISAT lines,
ICSH 361 was most affected by the disease, showing
the maximum infection score of 5. ICSH 193
was free of MDM virus symptoms.
Abstract:
Utilization of genetic resistance to diseases
D.J. Andrews, INTSORMIL Sorghum and Millet
Breeder, University of Nebraska, Lincoln, NE
68583, USA.
The importance of incorporating sufficient durable
disease resistance when breeding new crop
varieties is usually of equal importance as improving
grain yield and quality. However, as
with any breeding situation, the greater the
number of necessary objectives, the slower will
be the overall progress.
To be successful, before embarking on breeding
for disease resistance, the breeder needs basic
information on the nature of the problem:
1. The existing and potential damage to yield.
2. The threshold incidence when yield loss
begins.
3. Other factors that help control the disease.
4. The genetic basis for resistance—is it monogenic,
multigenic, recessive or dominant, etc.?
5. Existing races or biotypes? Is the pathogen
capable of rapidly evolving new biotypes?
6. Available sources of resistance? How good is
their resistance and how agronomically good
are their backgrounds?
7. Are there environments where resistant
plants can be consistently identified?
In fact, complete information is never available
and always some assumptions have to be
made. Each breeder should be aware, however,
that the more sparse the information, the more
limited may be the success of the effort. In any
case, elements 6 and 7 above are crucial to
success.
Pathologists should know that the overall
agronomic value of a source of resistance is very
important to a breeder. The best degree of resistance
is usually carried in some unadapted germplasm
accession, but a source with moderate,
though sufficient resistance (how much resistance
is needed to lower incidence to the threshold
value?) in an adapted background may be preferable
because of ease of utilization. For 7, some
method of statistically quantifying the degree and
consistency of the disease pressure in the selection
environment is necessary (e.g, from data on
replicated control plots of known resistant and
susceptible stocks).
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