RA 00110.pdf - OAR@ICRISAT

Large s c a l e f i e l d s c r e e n i n g
at ICRISAT Center
A c c e s s i o n s , b r e e d i n g
m a t e r i a l s 14 000 l i n e s each season
iliar to the original parental lines and the hybrid
( I C M H 84814) based on these lines is similar in yield
and other characteristics to BJ 104 (Table 4). However,
841A differs significantly from 5141A for several
characters, most notably for time to 50% flowering,
height, head length, and individual grain mass
(Table 4).
Pre-IPMDMN
150 e n t r i e s
( N i g e r i a , B u r k i n a Faso, I n d i a )
I P M D M N
50 e n t r i e s
( 1 0 - 2 0 l o c a t i o n s i n I n d i a , A f r i c a )
S t a b l e
r e s i s t a n c e
Breeding
E l i t e D M r e s i s t a n t c u l t i v a r s
Figure 2. Basic scheme for the identification and
utilization of downy mildew resistance.
Inheritance of Resistance
Little is known about the model of inheritance (Nene
and Singh 1976). In some cases the resistance was
demonstrated to be controlled by one or two dominant
genes (Appadurai et al. 1975, Singh 1974, Gill
et al. 1975, Gill et al. 1978), while in others it was
reported to be controlled polygenically and by additive
and nonadditive gene effects (Singh et al. 1978,
Basavaraj et al. 1980, Shinde et al. 1984). The overall
mode of inheritance is unclear because the parents
used in these studies were heterozygous, the pathogen
populations were highly variable, and inoculation
procedures were generally not standardized.
Homozygous parents for susceptibility and resistance
and uniform inoculum should be used in inheitance
studies. Laboratory screening such as the
newly-developed, seedling-inoculation technique
(Singh and Gopinath, 1985) will be useful.
Strategies for Control
Availability of resistant cultivars, an effective systemic
fungicide, and cultural practices provide opportunities
for the long-term management of this disease.
Table 3. Downy mildew ( D M ) reactions of three lines
reselected for DM resistance at several locations 1 in India.
Test
Entry year
241A1 1983
I C M P
84814 1984
7042 1982
7042 2
1
0
12
11
64
2
0
0
4
DM severity (%)
locations 1
3 4
0 0
1 -
0 0
33 30
5 6
0 0
- 2
4 7
63 92
7 8 9
< 1 9 -
8 13 3
4 9 0
57 67 52
1. Locations: 1. Aurangabad 2. Durgapura 3. Jamnagar 4. Coimbatore
5. Hisar 6. Patancheru 7. Ludhiana 8. Mysore
9. Kovilpatti
2. Mean of 3 test years.
Host-Plant Resistance
Growing one cultivar over a large area should be
avoided. Cultivars should be specified for particular
areas, and there should be several cultivars in given
areas. Success, however, will depend on the genetic
differences among the cultivars. Another approach
would be to use gene deployment over time. This
approach is based on the principle of host specificity.
It is likely that pathogenicity and consequently the
oospore population of the pathogen may increase if
a genotype is grown for a long period. Conversely,
the pathogenicity may decline if the specific host is
withdrawn from cultivation. This particular phenomenon
has been observed with N H B 3, at Durgapura
in Rajasthan (Singh and Singh In Press).
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