Sorghum Diseases in India

Effective screening techniques for mass
screening of sorghum genotypes have been
developed (Anahosur 1980,1987; Anahosur and
Hegde 1979). Genotypes are exposed to oospores
and to conidia. Some 800 varieties, 400
hybrids, 50 B-lines, and about 25 R-lines were
tested by 1987. The resistant genotypes (showing
less than 5% systemic infection) are SPV-35,
81,104,126,166, 291, 312, 346, 351, 462, 736, 775;
CSH-2,3,4,5,6; SPH-10,11,12,30,39,59,68,159,
176, and 185; DMS 1 B, 2219 B, 3660 B, 3691 B,
1202 B, 1807 B, M 12 B; CSV 4, PVK 3, PVK 10,
and MR 750.
A selection from Nandyal, in Andhra Pradesh,
DMRS 1 (IS 27042) was developed and
found to possess stable resistance to downy mildew
(Anahosur et al. 1984a). From International
Sorghum Downy Mildew Nursery (ISDMN), the
stable resistant genotypes are IS-3443, 27042,
22230, 22231, and 18757; these were completely
free from infection.
Breeding resistant varieties using IS 3443 and
IS 27042 is in progress at Dharwad. The cross SB
905(S) x DMRS 1 (R) has yielded several highyielding
progenies coupled with high levels of
resistance; 10 of these are in an advance stage of
evaluation. In India, hybrids developed on 2296
A (17.2-63.6% diseased) and 199 A (34-41.6%
diseased) were susceptible, whereas those produced
on 2219-A and 2077-A and DMS 1 B have
shown resistance (4.5-8.9%, 3.4-11.4%, and 1.7-
4.6% disease incidence, respectively).
Rajasab et al. (1979,1980a, 1980b) reported the
dispersal of conidia as far as 80 m for as long as 5
hours after midnight. Ramlingam and Rajasab
(1981) reported least infection from oospores
and maximum infection from conidia; thus
conidia are known to play major roles in epiphytotics.
Prabhu et al. (1983, 1984) reported the seedborne
nature of downy mildew in sorghum.
These workers detected mycelium in 40% of the
seeds and in 5% of the endosperm. Mycelium
was not found in the embryo. Kaveriappa and
Safeeulla (1978) expressed doubt as to the survival
of mycelium when seeds are sundried.
Shetty and Safeeulla (1981) reported oospore
germination by branched aseptate germ tubes
from weathered oospores. A study of the inheritance
of resistance to downy mildew (Rana et al.
1982a) reported that resistance is dominant and
controlled by three genes. Bhat et al. (1982),
using crosses 296(S) x QL 3 (R) and 296 (S) x
50
Uchv 2(R), reported that resistance is dominant
and controlled by four genes. We have studied
this aspect, using crosses DMRS 1(R) x QL 3(R),
269 B(S) x IS 3547(R), 296 B(S) x QL 3(R), and IS
3443(R) x QL 3 (R) and found that resistance is
dominant and controlled by three genes 57 (R):
7(S) or by four genes 243(R): 13(S).
Effective control of downy mildew by different
formulations of metalaxyl was achieved as
seed dress (Venugopal and Safeeulla 1978), and
as seed dress + spray (Anahosur and Patil 1980,
1983b). Sorghum downy mildew cure was also
reported (Anahosur and Patil 1980, 1981b) and
subsequently a spray schedule for cure was developed.
Metalaxyl applied to seed at the rate of
1 or 2 g a.i. kg -1 seed was not phytotoxic, but
when applied at 4,6, or 8 g a.i. kg -1 of seed it was
phytotoxic. Seeds treated at 1 or 2 g a.i. kg -1
could be preserved at room conditions for 9
months without affecting either the efficacy of
fungitoxicant or seed germination (Anahosur
1986a).
Ergot
Systematically estimated grain-yield losses from
ergot are not available, but heavy grain losses
are realized in commercial and seed-production
plots. All A-lines are highly susceptible. Extensive
screening of varieties, hybrids, A- and Blines,
R- lines, and some germplasms by artificial
inoculation show the less-susceptible (30% infection)
genotypes to be CS 3541, IS 3443, IS
14332, IS 3547, SPH 232, and DMS 1 B. The
screening procedure involves four evening
spray inoculations of a rich conidial suspension
on newly emerged earheads on alternate days
and then covering the heads with paper bags.
This helped to induce high disease pressure.
Evaluation was on a scale of 1 to 5, where 1= no
disease, and 5 = at least 51% spikelets infected.
Early sowings in Maharashtra, Karnataka,
and Gujarat avoided the disease (Sangitrao et al.
1979; Anahosur and Patil 1982a). The meteorological
conditions favoring honeydew development
were minimum temperatures of 18-
31°C, relative humidities of 65-85%, and drizzling
rains. Dry weather following the honeydew
stage favored sclerotia development
(Sangitrao and Bhade 1979; Anahosur et al.
1984b). In the Karnataka sowings, growth of
Cerebella sorghi suppressed sclerotia production.