RA 00110.pdf - OAR@ICRISAT

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A s e x u a l
s p o r e s
Oospores
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a
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Figure 2. Progressive development of leaf symptoms in pearl millet colonized by Sclerospora graminicola
(a) the pathogen colonizes the growing point of a seedling; (b) the tissues differentiated after colonization
appear systematically diseased when the organs subsequently grow out and unfold.
ment in the seeds (Subramanya et al. 1981). This
establishment might also be due to systemic infection.
As such seeds apparently look healthy, they
might be able to initiate the disease in the next
season. As a consequence, it is important to realize
that seed produced in the partially malformed heads
are known to contain internally borne mycelium.
Although seeds on such heads are usually not
selected for seed purposes, florets infected by sporangia
do not look any different from those which
are not infected, so seed from them could easily be
selected unknowingly for planting.
Seed as Inoculum Source
Conflicting reports about the seedborne nature of
downy mildew in pearl millet have generated a lot of
interest among pathologists. There are many reports
on the association of the pathogen with the seed to
serve as a primary infection source, in addition to
oospores present in the soil (Arya and Sharma 1962,
Suryanarayana 1962, Singh and Pushpavathi 1965,
Tiwari and Arya 1966, Sundaram et al. 1973,
Safeeulla 1976b). There are conflicting reports about
mycelium in the embryonic tissue. Shetty et al.
(1980b) reported that HB 3 race invariably showed
downy mildew mycelium in seed tissues, but the
Mysore local race did not infect the pearl millet seed.
It is likely that the pathogen prevalent in the areas
where the seeds were collected belongs to a race
which does not infect the seed. Shetty et al. (1977,
1978, and 1980a) demonstrated the seedborne and
seed-transmitted nature of 5. graminicola in pearl
millet seeds. They demonstrated that inoculum may
be present in pearl millet seeds either as external
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