Sorghum Diseases in India

and occurred more often at the leaf tips, suggesting
that hydathodes may be a portal of entry for
the bacteria. We did not detect bacterial leaf
blight symptoms on maize or sorghum in Nigeria,
even when these crops were growing adjacent
to or intersown with pearl millet.
Epidemiology of P. avenue
In growth chamber studies, bacterial leaf blight
was favored by hot (36/24°C) and moist conditions
(90% RH) (Akhtar and Claflin 1986a). In
Kansas, P. andropogonis and P. avenae were capable
of overwintering in infested plant debris
(Akhtar and Claflin 1986b). Leaf and stalk tissue
and seeds were examined by fluorescent antibody
staining (FAS) for bacteria every 2 weeks
from February through May. More bacteria were
observed in leaf tissue than in stalk tissue or in
seed samples. Neither of the bacteria species
was recovered from seed samples plated on
YDCA medium, whereas the pathogens were
easily recovered from stalk and leaf tissue.
Effect of sorghum growth stage on bacterial
stripe and bacterial leaf blight development
Three plants from each row of 26 grain sorghum
hybrids (four replications) were inoculated with
P. andropogonis and P. avenae at 30, 40,50, and 90
days after sowing in 1982 and 30 to 40 days in
1983 (Akhtar and Claflin, unpublished). This approximated,
respectively, Stage 3 (growing point
differentiation: seven to ten leaves), Stage 4 (flag
leaf visible in whorl), Stage 5 (boot), and Stage 9
(physiological maturity). Although our data (Table
3) showed Stage 9 to have the highest reading,
it is probably important in most years that
plants be inoculated prior to Stage 5. Climatic
conditions in 1982 were optimal for disease development.
In 1983, however, periods of hot and
dry conditions persisted and limited disease
was observed. Timely rainfall, warm temperatures,
overcast skies, and frequent dews after inoculation
appear vital for extensive disease
development.
Table 3. Effect of inoculating grain sorghum
plants at various growth stages with Pseudomonas
andropogonis and P. avenue. 1
Table 3. Effect of inoculating grain sorghum
plants at various growth stages with Pseudomonas
andropogonis and P. avenue. 1
Table 3. Effect of inoculating grain sorghum
plants at various growth stages with Pseudomonas
andropogonis and P. avenue. 1
Growth
stage 2
P. andropogonis P, avenae
1982 1983 1982 1983
3 2,45 3 b 4 1.76 a 1.39 a 1.09 a
4 1.97 c 1.11b 1.01 b 0.20 b
5 1.51 d 1.04 b
9 2.84 a 1.25 a
1. Source: Akhtar and Claflin, unpublished.
2. Growth stages: 3 = growing point differentiation
(7-10 leaves); 4 = flag leaf visible; 5 = boot stage; 9 =
physiological maturity.
3. Rating scale of 0-5, where 0 = no symptoms; 1 = 1-
10; 2 = 11-25; 3 = 26-50; 4 - 51-75; 5 = 76-100% of
leaf area affected. Each number represents an average
of 3 plants of 26 hybrids inoculated at each
stage of growth.
4. Numbers within a column not followed by a common
letter are significantly different at the 0.05 level
as determined by Duncan's Multiple Range Test.
Bacterial Spot
Causal organism
P. syringae cells are aerobic, gram-negative rods
measuring 0.5-0.7 x 0.8-2.2 µm. The cells are
motile with one or more polar flagella. P. syringae
produces a green fluorescent pigment on
KB. The bacterium does not hydrolyze starch;
catalase and aesculin tests are positive whereas
oxidase and indole production are negative.
Acid is produced from glucose, fructose, sucrose,
galactose, mannose, arabinose, xylose,
mannitol, glycerol, and sorbitol. Optimum
growth temperature is near 28 °C; maximum is
35 °C and minimum is 1 °C (Hayward and Waterston
1965).
Host range
Numerous monocot and dicot hosts, including
many genera from the Graminae family, are susceptible.
P. syringae is disseminated over long
distances by seed and plant debris. Bacterial
spot incidence is increased by cool weather, rain,
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