Sorghum Diseases in India

Bacterial Streak
Causal organism
X. campestris pv holcicola cells are gram-negative,
about 0.4-0.9 x 1.0-2.4 µm in size, and have one
or two polar flagella. Acid is produced from
fructose, galactose, glucose, mannose, and sucrose.
Casein and Tween 80 are hydrolyzed, but
starch is not. Gelatin is not liquified, oxidase is
not produced, nitrates are not reduced, and malonate
can be the sole source of carbon. X. c, pv
holcicola will not grow at 4° or 41 °C. Bacterial
growth is slow; colony development requires 4
to 5 days. Colonies on YDCA are yellow, circular,
convex, and very viscous (Qhobela and
Claflin, unpublished).
Host range
Hosts for X. campestris pv holcicola include Sudangrass,
maize, sorghum, broomcorn, and Johnsongrass.
Pathogenicity tests were negative on
sugarcane, pearl millet, finger millet, and proso
millet (Qhobela and Claflin, unpublished). Bacterial
leaf streak has been reported from South
America, North America, Mexico, Australia, Africa,
New Zealand, the Philippines, and the
USSR (Commonwealth Mycological Institue
1987).
Epidemiology
Growth chamber studies at 50, 75, and 90% RH
showed that bacterial streak is not influenced by
high relative humidity levels (as is bacterial
stripe), but optimal temperatures for disease expression
were the same (30/24°C). (Claflin and
Machtmes, unpublished).
Symptoms of bacterial streak are often very
similar to those of bacterial stripe. Small interveinal
water-soaked lesions are initial symptoms.
With favorable climate, the lesions may
extend to 30 cm and often coalesce to produce
blotches covering most of the lower portion of
the leaf (Fig. 8). Color of lesions corresponds to
Figure 8. Bacterial streak on sorghum cv B 35-6 caused by Xanthomonas campestris pv holcicola.
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