Sorghum Diseases in India

Zambia, and Zimbabwe. Several entries with
outstanding resistance have been identified and
will be tested to confirm their resistance.
Other leaf spots. Epiphytotics of gray leaf spot,
oval leaf spot, and zonate leaf spot, occurred
regularly at several locations in Malawi, Zambia,
and Zimbabwe. Selections for leaf health
were made where epiphytotics occurred. Sources
of resistance identified elsewhere (India, western
and eastern Africa, and Texas A&M University
(INTSORMIL) are being tested.
Stalk and root rots. Fungi affecting the stalk included
Macrophomina phaseolina, Fusarium spp,
and Colletotrichum graminicola (Angus 1965,1966,
pp. 65-68; Rothwell 1983; Shao 1984; Botswana:
Ministry of Agriculture 1987; McLaren, personal
communication 1988). Fusarium spp caused root
rots (Shao 1984, McLaren, personal communication,
1988). Charcoal rot occurred in areas where
the crop was exposed, especially following anthesis,
to drought stress and high temperatures
such as occurred in Botswana, Lesotho, Tanzania,
and Zimbabwe. In several countries charcoal
rot is not officially reported on sorghum,
(e.g., in Angola, Lesotho, Malawi, Swaziland, or
Zambia). Considering the wide host range of the
pathogen, it may be present there, and this requires
investigation.
Certain high-yielding varieties [e.g., SV 2 (A
6460), SAR1 (ICSV145) -1-1-1, SPV 475, and ZSV
1)1, and hybrids (e.g., PNR 8544), appeared to be
susceptible to charcoal rot in Zimbabwe. Lines
identified as resistant elsewhere by ICRISAT
and INTSORMIL are being tested regionally.
Identification of the pathogens causing stalk
and root rots in these areas requires additional
study.
Inflorescence Diseases
Inflorescence diseases are caused by viruses and
fungi.
Viral. The maize dwarf mosaic and sugarcane
mosaic viruses cause stunting, fewer seeds and
reduced seed mass.
Fungal. Important fungal diseases that attack
sorghum inflorescence include: ergot, grain
molds, and smuts.
16
A. Ergot
From Tanzania (Doggett in Williams et al. 1980)
to South Africa (McLaren, personal communication
1988), this disease is of particular importance
in male-sterile lines. It is a particular
problem in late-sown sorghum and in the Republic
of South Africa, where sorghum is grown
under center-pivot irrigation (McLaren, personal
communication 1988). In 1987, ergot epi-
. phytotics occurred for the first time in Lesotho
and Malawi. Cooperative work with the Imperial
College in London, and the University of
Zimbabwe, was initiated to learn more about the
ergot life cycle, the toxicity of sclerotia, and the
development of artificial screening techniques.
In cooperation with ICRISAT's EARSAM network,
attempts to identify germplasm with resistance
to ergot will begin.
In Zimbabwe, year-old conidia were able to
cause infection. Time to production of honeydew
was similar (7-15 days) to that recorded in
the United Kingdom. Infection occurred even
during extended drought in 1987.
Sclerotia were formed at most locations with
ergot infections in Botswana, Malawi, Swaziland,
Tanzania, Zambia, and Zimbabwe. In
darkened growth chambers, mature sclerotia
harvested at the end of the rainy season (March),
germinated over a wide range of temperatures
(4-37°C). Germination percentages were low
(less than 20% of sclerotia).
The importance of ergot is related to the use
of hybrids. It is expected that hybrids will become
more popular and that therefore this disease
may become more important because of its
interference with seed production.
B. Grain molds
Several newly released and prereleased varieties,
such as SV 1 (Zimbabwe) and certain hybrids
(e.g., PNR 8544), were susceptible to grain
molds. The hybrid DC 75 was relatively resistant.
It is expected that with the increase of
popularity of the nonphotosensitive varieties
and hybrids, grain molds will increase in
importance.
In the last 10 years, ICRISAT grain mold resistance
nurseries have been operating, but the material
lacked agronomic eliteness and was not
used by breeders. Agronomically elite material