Sorghum Diseases in India

Downy Mildew
The downy mildew organism induces systemic
and rarely local infection on pearl millet. Systemic
symptoms can appear at any growth stage
from seedling to flowering. However, except in
highly susceptible genotypes, infection of seedlings
is rarely seen in western Africa. Infection
by S. graminicola generally produces malformed
inflorescences with various degrees of transformation
into leafy structures called green ears.
This prevents inflorescence development and
thus is detrimental to grain yield (Girard 1976;
Girard and Delassus 1978).
In a survey of farmers' fields in Niger, downy
mildew (DM) incidence varied from nil (lowrainfall
area) to 30% (high-rainfall areas) (ICRI-
SAT 1985). In the north of Cameroon, DM incidence
was from 10 to 29% (IRA/ICRISAT 1987)
and in Nigeria from nil to 15% (Selvaraj 1979).
An unpublished crop-loss study in Gaya, Niger,
showed a yield loss of 50% due to DM attack; in
Nigeria losses were from 4 to 22% (Selvaraj
1979).
Pathogen variation has been demonstrated
with various procedures by many researchers
(Ball and Pike 1983, 1984; Shetty and Ahmad
1981; Girard 1976; Selvaraj 1979). The differential
pathogenic reaction of DM isolates in India and
in western Africa is a major reason why millet
cultivars improved and produced in India are
not adapted to most countries of western Africa.
The WADMVN
ICRISAT's Western African Downy Mildew
Variability Nursery (WADMVN), initiated in
1986, provides useful information on the pathogenic
variability of DM within the western African
region. This nursery includes varieties,
hybrids, and breeding lines from India and
western Africa (10 entries) and is sown as a "differential"
The same seed sources are to be used
for 3 years. Results from the 1st year have demonstrated
striking differences between Burkina
Faso, Nigeria, Niger, and Senegal for pathogenicity
of S. graminkola (ICRISAT 1987b). Evidence
for differences in virulence among the
four locations was especially noticeable for NHB
3,81 B, and MBH 110 (Table 2). To test stability of
resistance, breeding products must be exposed
to a range of DM pathotypes in different environments.
In view of these requirements, ICRISAT has
initiated the Western African Downy Mildew
Observation Nursery (WADMON). This is a regional
cooperative activity through which pearl
Table 2. Downy mildew (DM) incidence (%) of the Western African Downy Mildew Variability
Nursery (WADMVN), at Bambey, Bengou, Kamboinse, and Samaru, rainy season 1987.
DM incidence 1 (%) at dough stage
Entry Designation Origin Mean 2 Bambey 3 Bengou 4
700651 Breeding line
IKMV 8201 Variety
INMV 8220 Variety
MBH 110 Hybrid
NHB 3 Hybrid
81 B Maintainer
IAR, Nigeria
INERA/ICRISAT
Burkina Faso
IAR/ICRISAT, Nigeria
India
India
ICRISAT, India
1
3
3
27
30
43
0 1
0 3
5 4
4 30
1 21
4 69
Kamboinse
5 Samaru 6
Trial mean (10 entries) 14 5 15 15 20
1. Based on a mean number of 69 to 90 plants per entry in two replications and two rows per replication.
2. Mean of all locations ranked.
3. Institut Senegalais de Recherches Agricoles, Senegal.
4. ICRISAT Sahelian Center, Niger.
5. Institut d'Etudes et de Recherches Agricoles, Burkina Faso.
6. Institute for Agricultural Research, Nigeria.
110
0
1
3
74
58
0
4
6
0
0
38
100