Sorghum Diseases in India

of resistance to grain deterioration (e.g., early
infection, endosperm texture, phenol, etc.).
5. Design experiments on biochemical mechanisms
of host-plant resistance. Utilize histological
study techniques, including measurement
of microbial presence and damage. Use
chemical (ergosterol, ELISA, etc.) as well as
histological techniques.
6. Continue searching for sources of resistance.
Screen landraces, local varieties, and photoperiod-sensitive
hybrids.
7. Study the epidemiology of microbial degradation
of seeds.
8. Compare routinely the GM situation on sorghum
with microbial deterioration of other
grains of other crop species.
Sorghum Downy Mildew (SDM)
1. Variability of virulence in Peronosclerospora
sorghi is a major concern. We recommend continuation
of the current ICRISAT multilocational
survey for virulence in P. sorghi, with
expansion to include additional entries of resistant
materials from participating countries.
2. Initiation and continuation of research to
identify the type and amount of variability
among the genetic factors in sorghum that
confer resistance to SDM, as well as studies to
determine the genetic relationships among resistant
genotypes.
3. Host resistance to P. sorghi conferred by oligogenic
or polygenic is preferable to monogenic
resistance. We recommend that genetic
combinations be found (or developed, if necessary)
and utilized in sorghum-improvement
programs.
4. Plant characters active in enabling sorghum
to escape DM, but not directly involved in the
host-pathogen interaction, may provide a
means of controlling SDM without placing selection
pressure for virulence on the pathogen
population. We recommend research to identify
these plant characters and determine
their potential in SDM-control programs.
5. The inability to induce consistent germination
of P. sorghi oospores restricts the use of this
spore form in SDM-resistance screening, and
hinders research on the genetics of virulence
in P. sorghi. We recommend the development
of effective oospore-germination techniques
for use with P. sorghi
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6. Metalaxyl provides effective control of SDM,
but the possibility that the pathogen will develop
metalaxyl-resistant strains exists. We
recommend the development of an alternative
chemical control.
7. We recommend continued formal and informal
cooperation and communication between
organizations and individuals engaged
in SDM research. Much of the considerable
success to date is attributable to a spirit of
working together.
Leaf Diseases
1. Effects of diseases on sorghum plants differ
at different growth stages. This knowledge
for each pathogen would be very valuable.
2. Development of a standard international rating
scale, based on leaf area infected, and
sufficiently flexible and sensitive for use in
detection of resistance and in disease progress
studies is vital. Growth stages at which
plants are to be rated must be standardized.
3. We recommend that studies be initiated on
techniques for estimating the effect of prevalent
diseases on grain and fodder weights in
given localities.
4. In view of the importance in evaluating sorghums
for resistance, development of effective,
practical, and reliable inoculation
techniques for this purpose is essential.
5. Continuation and expansion of international
cooperation in multilocational evaluation
and characterization of germplasm response
to foliar pathogens, along with exchange of
elite germplasm, is essential. We recommend
that entries should include international
and local susceptible controls.
6. Efforts to identify, collect, and preserve landraces
and other sorghum germplasm should
be intensified, as should be the search for
resistant sources.
7. Development of foliar disease resistance,
i.e.,:
a. effective across variable environments;
b. durable through reduced selection pressure
for physiological variants within a
pathogen population; and
c. active against several foliar pathogens,
especially during vulnerable growth
stages of the host.