Sorghum Diseases in India

Thomas: 1. Striga hermonthica; and 2. Only
groundnut was tested.
Obilana: Primarily you are right in saying that
intercropping reduces Striga in sorghum and
groundnuts. Secondly, what is observed is not the
result of cooler soil temperature, but the effect of
groundnut as a trap crop, causing suicidal germination
of the Striga seed, and thus reducing the
number of Striga plants emerging. Please cooperate
closely with the Striga workers (ICRISAT and
national scientists) active in the western and southern
African regions and the ICRISAT Center.
Guiragossian: Some diseases—such as gray
leaf spot, rust, or leaf blight that appear after
flowering—might not affect yield significantly,
yet are important because they reduce acceptability
by farmers. Therefore one should conduct
a survey with farmers to find out whether
such diseases affect farmers' decisions to accept
or reject a variety or hybrid.
Thomas: This is true. We do intend to continue
screening for gray leaf spot in hot-spot locations.
Our final materials must have acceptable levels
of resistance to all leaf diseases. However, a disease
like gray leaf spot, which we suspect causes
little damage, will have the lesser emphasis in
our program.
Balasubramanian:
1. Have you developed an inoculation technique
to screen sorghum lines against Rhizoctonia
solani?
2. Does the cultivation of rice affect the incidence
of Rhizoctonia blight of sorghum?
Kimigafukuro:
1. We inoculate with TO g of R. solani cultivated
on barley grain at the base of each sorghum
seedling and then cover with vinyl film to
keep the plant moist.
2. The increase of Rhizoctonia disease of sorghum
has a major effect on the cultivation of
rice, because the causal organisms of banded
leaf and sheath blight on rice and on sorghum
both belong to anastomosis group 1 of R. solani.
Anahosur: Elaborate on the inoculation technique
and maintenance of inoculum of Phyllachora
sacchari in sorghum.
Dalmacio: P. sacchari is maintained by screening
sorghum continuously. Tar spot development is
promoted through creation of a humid environment.
Infected sorghum leaves serve as inoculum
and inoculation is done either by spreading
infected leaves along the rows or by attaching
infected leaf sections to leaves of test material
using a paper clip.
Adipala: Have you carried out cross-inoculation
trials with the Rhizoctonia solani isolates
from rice and sorghum?
Dalmacio: No, but we believe that R. solani isolates
infecting rice also infect sorghum.
Theuri: What form of rotation is used on sorghum
with respect to Rhizoctonia? Do the Rhizoctonia
isolates from rice attack soybeans?
Dalmacio: Sorghum is used in rotation with
corn and in some cases with rice. Where used as
such, sorghum sowing coincides with dry environment
and Rhizoctonia does not develop to a
level that it damages sorghum.
Balasubramanian:
1. Have you developed an inoculation technique
to screen sorghum lines against Rhizoctonia
solani?
2. Does the cultivation of rice have any influence
on the incidence of Rhizoctonia blight of
sorghum?
Dalmacio:
1. Yes, we have developed the leaf-sheath inoculation
technique; it consists of growing the
fungus on sterilized sorghum grains and
placing 5 to 10 infested sorghum grains at the
axil of the leaf blade two internodes above the
ground.
2. No, because when sorghum is rotated with
rice, sorghum sowing coincides with the dry
season, an unfavorable time for development
of Rhizoctonia solani.
House: Why has the production of sorghum declined
so much in the last few years?
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