RA 00110.pdf - OAR@ICRISAT

Table 4. Comparison of BJ 104 and 5141A with their downy-mildew resistant counterparts, I C M H 84814, and 841A,
I C R I S A T Center, rainy season 1985.
Entry
Tillering
(no)
Time to 50%
flowering
(d)
Plant
height
(cm)
Head
length
(cm)
Head
mass
(kg ha -1 )
1000 grain
mass
(g)
Grain
yield
(kg ha -1 )
I C M H 84814
BJ 104
841A
5141A
2.8
3.8
3.1
3.3
44
42
53
51
127
111
106
96
15.9
16.3
15.0
11.5
2800
3000
1600
1600
6.9
6.5
5.8
4.9
2100
2100
1100
1000
Mean 1
2.4
44.4
120.0
15.8
3000
6.8
2100
S.E.
±0.2
±0.5
±2.1
±0.4
±275
±0.22
±200
1. Mean of 17 entries including 13 reconstituted hybrids that were evaluated in the trial.
Open-pollinated cultivars in which every individual
is genetically different provide another opportunity
to keep the disease under control. Due to their
heterogeneity, such cultivars will have a buffering
effect against D M . They are unlikely to be diseasefree,
but they will not develop the disease in epidemic
proportions for several years. ICRISAT is putting
major emphasis on open-pllinated varieties. In
Africa, where hybrids are not currently being grown
for various reasons, open-pollinated cultivars will be
the most appropriate genotypes for DM control.
years is the only method to detect the durability of
resistance. Stability (multilocational tests), has been
suggested as one method which might predict durability
(Johnson 1984), but which whould need testing
over time. Moreover, durable resistance to systemic
diseases like DM in which a plant can be either
diseased or healthy, should be viewed differently
from leaf spots and rusts. Therefore, to make the
resistance durable, a system must be identified in
which the pathogen can parasitize each plant without
adversely affecting its yield.
Fungicides
Metalaxyl is a powerful tool to control DM in pearl
millet. Although the inefficacy of metalaxyl has been
reported for some other diseases, it can still be used
effectivewly for control of downy mildew of pearl
millet if the strategies for its use are carefully worked
out. The best strategy would be to keep the fungicide
in reserve, for use only if the resistance breaks down
unexpectedly.
Cultural practices
Of the many cultural practices known, only roguing
infected plants soon after their detection is strongly
recommended. This should be done even if other
control methods, including resistant cultivars, have
been used.
Research Priorities
Durable Resistance
Cultivation of varieties over a large area for many
Basic Genetic Studies
With the available knowledge of variation in the
pathogen population, frequencies of virulence genes
need to be assessed. Likewise genes for resistance in
the host should be determined. To utilize the identified
resistance by the appropriate breeding procedures,
the pattern of inheritance should be studied.
Nature of Resistance
Resistance may operate before or after penetration.
During the prepentration stage, spore germination
may be inhibited due to certain chemicals, or there
may be barriers to penetration by mechanical or
physiological factors. After penetration, several factors,
including incompatability, reduced colonization,
and sporulation (slow mildewing) may stop
and/or delay disease development. A l l these aspects
need to be studied. Research is needed to identify
lines with reduced colonization and sporulation, and
to further improve these traits by appropriate selection
methods.
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