Sorghum Diseases in India

2. In the past, farming was in the wild ecosystem
and all fields, even in large-scale farming,
were surrounded by bush. Now human pop
ulations have increased rapidly and new governments
are pushing expansion of agriculture.
In some countries (such as Lesotho, Malawi,
and the Republic of South Africa) large
areas are covered by agricultural crops. The
sorghum fields are close to each other, and
spread of diseases is a natural consequence.
Southern Africa also saw changes that should
be helpful in avoiding crop losses from disease.
Through the establishment of the Southern
Africa Development Coordination Conference
(SADCC), regional coordination and cooperation
increased and an enthusiastic effort in
regional testing and resistance screening of national
and international sorghums began. Promising
sorghums are intensively tested at hot
spots and in disease sick plots throughout the
region. In the 1985/86 rainy season, a regional
cereals pathology program was initiated with
four major objectives:
1. Identification of the major diseases and the
major-disease hot spots.
2. Adaptation and development of screening
techniques effective for major sorghum diseases
in southern Africa.
3. Identification of sources of resistance to these
diseases.
4. Disease monitoring and surveillance.
Most national programs (Botswana, Lesotho,
Malawi, Swaziland, Tanzania, Zambia, and Zimbabwe)
began to develop expertise to test disease
resistances, and a beginning was made to
identify regional crop vulnerability through the
SADCC/ICRISAT Sorghum and Millets Improvement
Program.
Sorghum Diseases in Southern Africa
My comments on the importance of disease
groups in relation to sorghum production in
southern Africa will include (1) seed rots and
seedling blight, (2) foliar diseases, (3) stalk and
root rots, (4) inflorescence diseases, and (5)
witchweeds. Nonparasitic diseases, such as aluminum
toxicity, iron chlorosis, salt damage, and
zinc deficiency, do occur in the region. Agrono­
mists and breeders have considered these in
crop improvement programs, but the discussion
here is limited to pathogen-related diseases and
Striga.
Seed rots and seedling blight
Fungi damaging the endosperm and embryo of
seed and causing seed rots include: Aspergillus
spp, Fusarium spp, Penicillium spp, and Rhizopus
spp. Seedling blights were caused by Exserohilum
turcicum, Fusarium spp, Macrophomina
phaseolina, Mycosphaerella holci, Phyllosticta sorghiphila,
Peronosclerospora sorghi, Pythium spp,
Rhizopus spp and Rhizoctonia spp (McLaren 1983;
Rothwell 1983). Nematodes that caused seedling
blight were Pratylenchus spp (Page et al. 1985)
and Meloidogyne spp. Other fungi and nematodes
may be encountered once attention can be
given to detailed study of these diseases. The
importance of seed rots and seedling blights is
still largely unknown. Poor stand establishment
occurred in cool and wet soils in Lesotho (Ndimande,
personal communication 1982) and the
Republic of South Africa (McLaren, personal
communication 1988). Other causes for poor
stands, however, still need to be determined. In
downy mildew (DM) sick plots in Zambia and
Zimbabwe, seedling blights reduced stands by
more than 50%.
Foliar Diseases
Foliar diseases in southern Africa are caused by
viruses, bacteria, fungi, and nematodes.
A. Viral diseases
Advanced research on detection and identification
of viruses has been done in South Africa. In
1985, Zambia and SADCC/ICRISAT Sorghum
and Millets Improvement Program initiated a
cooperative effort with Texas A&M University,
USA to identify viruses; in 1987, the project was
expanded to include ICRISAT Center in India,
Kansas State University (INTSORMIL) in USA,
and ICRISAT's EARSAM network as cooperators.
Since 1986, the testing of differential nurseries
and identification of sources of resistance is
ongoing in a virus sick plot, making use of early
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