Sorghum Diseases in India

Symptoms. The disease is characterized by the
presence of chlorotic and rectangular spots with
a white powdery appearance (conidial formation),
especially on the undersurface of the leaf
blades. Later, the spots change to light brownish
necrotic lesions without conspicuous border
coloration.
Causal organism. Conidiophores extrude
through stomata singly or in tufts of 2 to about
12. They are geniculate then denticulate towards
the apex, 22-80 by 3.6-6.9 µm in size, and with
or without septa. Septa may be up to five in
number. Conidia are obclavate with an obconic
then truncate bottom and attenuated then blunt
apex, from 21-55 by 3-6 µm in size, with one to
six (mostly three) septa.
The morphology of the fungus is similar to
that of the yellow spot fungus (Cercospora koepkei
Kruger) of sugarcane, in many cases without
parasitism. Therefore, the sorghum fungus was
designated as C koepkei Kruger var. sorghi (Goto
et al. 1962).
Banded leaf and sheath blight
Banded leaf and sheath blight, caused by Rhizoctonia
solani, is a minor disease of sorghum in
other countries. However, it is very common in
Japan, due to the warm and humid weather that
is conducive to its development and spread in
summer. It is anticipated that the disease will
become more important, as the causal organism
belongs to the same strains (anastomosis group
1) of R. solani Kuhn that cause banded leaf and
sheath blight, important diseases of rice and
corn. The cultivation of sorghum is expected to
expand into areas currently planted to rice and
corn.
Resi stance to banded leaf and sheath blight is
an important objective in the breeding of new
sorghum varieties in Japan. At the Nagano Prefecture
Chushin Agricultural Experimental Station,
studies based on the percentage of plant
length infected to total plant length were initiated
to estimate the degree of resistance to banded
leaf and sheath blight. Estimation of disease
incidence by this procedure revealed a highly
positive correlation to the yield decrease caused
by the disease (Table 3).
The percentage of plant length infected to total
plant length in 72 varieties and of sorghum
infected artificially with R. solani are presented
in Table 4.
Table 3. Correlation between the percentage of
plant length infected with Rhizoctonia solani
to total plant length and yield decrease. 1
Sampling
Coefficients
date Foliage Ear Total
22 Jul
12 Aug
2 Sep
0.866**
0.418
0.533**
0.881**
0.824**
0.873**
1. Source: Kasuga and Takizawa (1984).
0.923**
0.771**
0.816**
Table 4. Grouping of varieties or strains of sorghum based on the percentage of plant length
infected artificially by Rhizoctonia solani to total plant length. 1
Plant length
infected (%) Varieties or strains
90 JN 2-2-1, JN 2-2-2, JN 4, JN 5, JN 7, KS-57A, SD102
1. Source: Kasuga and Takizawa (1984).
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