Sorghum Diseases in India

If it is argued that oospore infection is too
variable to use in this technique as the basis of a
screening procedure, then I must point out that
this difficulty will also apply to your current selection
procedure: the outcome of my suggestion
and your outcome are both predicated on
the same process and set of infection events.
Survivors of my suggested selection/screening
procedure should not be recorded as escapes.
With respect to inoculum, my suggestion
meets the ceteris paribus requirement and the differences—if
there are any—from the analysis of
variance (assuming that the rules of biometry
are followed) can be assumed to measure differences
in the resistance response to infection.
Balasubramanian: In the light of Webber-Fechner
law, the classification of disease-rating
scale in the field will geometrically take care of
many errors. Why should we not continue the
testing scale which exists today in many laboratories
(25% of plants) to quantify disease?
Putter: The principle of scaling which I demonstrated
comes from Mathew and Jinks. It shows
the influence of varous methods of transforming
the data points or scale values after these have
been collected. The Webber-Fechner law and its
logarithmic implications, as these were explored
by Horsfall and Barratt, influence the way in
which we arrive at the values that will subsequently
be submitted to scale-transformation
processes of the kind described by Mathew and
Jinks and which I have emphasized in my
presentation.
Osmanzai: In your presentation of yield regressed
on SDM, the dots looked dispersed.
Have you checked the significance of r 2 ?
Wall: It was significant at the 0.01 level, and it
was included in the statistics presented. Other
models, such as quadratic, polynomial, and exponential
were tried, but were not satisfactory.
Osmanzai: Do you consider the inclusion of climate
and sowing data as an important parameter
in the model for assessing yield loss because
of SDM?
Wall: I dealt with critical point models, and furthermore,
with models that allowed practical
application. The climatic influence is there, only
it is not separated. Climatic factors are important,
and they can be included in models.
de Milliano: How do you think your crop-loss
assessments apply to other regions in the world?
Wall: The particular models we developed are
applicable, strictly speaking, to the specific combination
of factors that existed during that season
and in that location. To simplify a model,
either in time or season, or in regions or locations,
one would have to take data for various
seasons or at various locations, and include
them when developing the model.
Zummo: Why is it that there is not much importance
attached to Striga research?
Chivinge: There is too little documentation on
the importance of Striga and its effects on crop
yield and the lack of manpower to specialize on
Striga in developing countries.
Guiragossian: National programs in eastern
Africa have realized that Striga is an important
problem in sorghum production. For that reason
the national programs of Ethiopia and
Sudan are taking the problem seriously and
have hired experts to develop strategies to
overcome the problem. The national program
scientists should request that ICRISAT take
Striga seriously.
Hulluka: I suspect that Striga has received less
attention than other pathogens because it is not
a problem in the developed countries.
Mbwaga: When we say a plant is resistant to
Striga does it mean the plant stops producing
Striga-germinating stimulants?
Kebede: It could be a low stimulant-producing
line or the cell walls of the root may be difficult
for Striga to penetrate.
Craig: Did the F1 and F2 plants of a given R x S
cross come from the same seed lots for the 2
yearly tests conducted?
Beninati: No. The F2 populations all come from
the same parental plants, but not necessarily
from the same F1 plant.