Sorghum Diseases in India

zeae of about 1000 nematodes in 1000 cm 3 soil
were associated with poor sorghum growth.
Soil populations of plant-parasitic nematodes
are considered to be at a level that is causing
damage when they are more numerous than
1000 in 1 L of soil. Known nematode pests found
in the roots, e.g., soil, Pratylenchus zeae, are always
assumed to be causing some damage.
Adipala: Dr Page, on the Zimbabwe side/were
nematodes actually isolated from the finger millet
and was the pathogenicity of these isolates
tested?
Page: Pot experiments have shown that Meloidogyne
javanica can reproduce and cause stunting
in finger millet.
Mushonga: Has there been an effort by nematologists
to associate plant type and species of
nematodes?
Page: We did not record whether the red or the
white sorghum types were most affected by
nematodes during our survey in Zimbabwe. We
have not been able to test the pathogenicity of
these nematodes that we found, during the survey
on sorghum, due to staff shortages. We have
been concentrating our research on maize, as it
is the preferred crop in Zimbabwe.
Kebede: When we talk about Striga spread, is it
a physical spread, or susceptible varieties being
grown, or optimum condition being present for
Striga germination? Resistance in any given variety
may have to be qualified in view of the
existence of biotype, ecotype, and strain.
Obilana: Striga spread can be both physical or
cultural. Physical as to movement by soil erosion
water and cultural by growing susceptible/tolerant
cultivars that allow Striga to form seeds for
next season. We are always specific when we say
a cultivar of sorghum/millet is resistant, either
to species or at a specific location or environment.
Dube: What conditions are necessary for the solarization
control strategy to be fully effective
against Striga?
Obilana: High temperature, high humidity, and
a polyethylene sheet The first two conditions
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are easily attained in irrigated fields or in southern
Sudan or in the Guinea Savanna of western
Africa where rainfall reaches 1200 mm per
annum.
Dube: You talk of exposing fields in the solarization
strategy-—just what time period are you implying
— 2 weeks, 4 weeks, or 6 months?
Obilana: As I had indicated, the solarization
method of Striga control is new and is being
investigated. The exact period for polyethylene
sheet cover is under investigation.
Thomas: In your discussion on survival mechanisms,
you mentioned the ability of Striga to
form biotypes. In your opinion, how strong is
the evidence for the existence of biotypes? Do
biotypes of Striga explain why at some locations
Framida has very low levels of Striga and can be
classified as tolerant or resistant, while in other
locations Framida is heavily attacked by Striga?
Obilana: Evidence for existence of biotypes is
strong; it abounds in the literature. It explains
the differential reactions of sorghum cultivars,
like Framida, in different locations-with different
biotypes of Striga.
Vidyabhushanam: The crop loss estimated to
Striga in India of 20% is not realistic. Since Striga
incidence never follows a definite pattern, this
kind of comment cannot be made. Please correct
your paper.
Obilana: These estimates are from the recent literature
on crop loss estimates for S. asiatica in
India [Vasudeva Rao, Chidley, and House
(1987)].
El Hilu Omer: Do antitranspirants have any advantage
over contact herbicides? Do they need
to be used ferquently for effective control?
Obilana: Yes. Antitranspirants are less toxic
than contact herbicides, and they are less
expensive.
Guiragossian: You referred to manure application
as no input. Please explain!
Obilana: In this paper for your proposed control
strategies/ by input I mean activity or sup-