Sorghum Diseases in India

Casela: Yes, I have.
Garud: Is sugarcane acting as a source of inoculum
for (SCMV) in sorghum? Which was the
important strain of SCMV occurring on sorghum?
Wall: Serology tests were performed only on infected
sorghum plants. MDMV strains A and B
predominated.
Frederiksen: Do the moderately resistant sorghums
in your conidial-inoculation trials for reaction
to sorghum downy mildew have similar
levels of resistance in the field?
Teyssandier: We have not demonstrated the relationship
between laboratory and field infection.
We believe that genotypes that consistently
show low sporulation rates under artificial inoculation
will probably have less inoculum pressure
in the field, preventing or delaying an
epidemic.
Mughogho: In your evaluation of sorghum
lines for resistance to the new virulent
pathotype of sorghum downy mildew, you
showed QL 3 to be resistant and susceptible.
What does this mean?
Teyssandier: That means that occasionally, even
using QL 3 India, we obtained about 4 plants out
of 25 inoculated with SDM. It could indicate that
the line is not homozygous for this character. We
need to analyze the line for genetic purity, as
suggested by Dr Craig.
Thomas: It would perhaps be useful if you give
a brief description of the screening techniques
you use for grain mold and sprouting.
Teyssandier: We use a field-lab technique
where sorghum entries are inoculated at anthesis
with a Fusarium moniliforme suspension.
Panicles are harvested at maturity and 400 seeds
per entry are germinated in a blotter for 1 week.
We classified the entries as tolerant or susceptible,
using a 1 to 5 scale according to the percentage
of molded grains. A score of 1 means no
fungal colonization, and a score of 5 means more
than 75% of the grains have fungal colonies.
To screen for tolerance to sprouting, we expose
mature panicles from different genotypes
to stable environmental conditions with very
high relative humidity and temperature between
25 and 28 °C. The speed of symptoms development
is used as a selection criterion.
Entries sprouting in 3-4 days are considered
susceptible, the ones that don't sprout in at least
10 days are considered tolerant.
Qhobela: What was the bacterial pathogen that
you inoculated into sorghum stalks?
Teyssandier: We have not identified the agent.
Njuguna: You have mentioned that Acremonium
strictum is an important pathogen in Central
America. Does this organism infect maize and,
does it not cause an important problem in
maize? Are there sorghum cultivars resistant to
Acremonium strictum?
Wall: (in response to the query regarding resistant
sorghum cvs) Yes!
Mughogho: (commenting on cross-inoculation)
I have not come across any publication on crossinoculation
studies of Acremonium strictum infection
on sorghum and maize. However, taxonomically
it appears that the pathogen of
maize is similar to that of sorghum. There is this
obvious need for cross-inoculation studies.
Laing: The breeding approach adopted in Mexico
appears to be perfect for the development of
vertical resistance and therefore "boom and
bust" cycles. I question the utility of this in view
of the pathogens faced and the needs of subsistence
farmers for stable resistance. I suggest a
more valuable approach is to seek horizontal resistance
(as was done in the FAO Programs)
such as those successfully conducted by Martin
Beek and Walter de Milliano on wheat in Brazil
and Zambia.
Laing: Please confirm that the Mexican breeding
program for downy mildew resistance is to
seek a resistance source and then backcross that
source of resistance into agronomically desirable
cultivars.
Narro: The breeding strategy adopted is to
cross Texas resistant materials into locally
adapted material, and then test the backcrossed
material in a Mexican "hot spot".
351