Reactions of certain commercial cotton cultivars to bacterial blight, Xanthomonas citri pv. malvacearum

Authors

Abstract

Bacterial blight of cotton caused by Xanthomonas citri pv. malvacearum is an
important quarantine disease in the country. To date, no official report exists on the
susceptibility or resistance assessments of different cotton varieties to the disease in
greenhouse conditions. To achieve this aim, disease incidence and severity in the three growth
stages of cotyledonary, flowering and boll formation for 8 cotton varieties under greenhouse
conditions (mean T.38/31; d/n and RH% 58/65 d/n.) were evaluated using a completely
randomized design with six replicates. Bacterial inoculum was prepared by mixing the
inocula of 5 X. citri pv. malvacearum isolates that was adjusted at concentration of 106
cfu/ml. The leaves were pricked with sterile needle and sprayed with bacterial inoculum for
three successive days at the flowering stage. Three weeks old bolls were pricked with needle
at 2 points and inoculated with cotton plugs soaked in bacterial suspension. Distilled water
was used as control. An in vitro (moist chamber) experiment on cotton bolls was also carried
out in a completely randomized design with six replications. Hunter,1986 and Hillocks, 1988
evaluation systems were used for leaf and boll susceptibility or resistance assessments
respectively. Results indicated that the local cultivar Bomi (G. herbaceum) was the most
susceptible among the eight cultivars studied here. In contrast, the three cultivars, Siokra,
Syndose and Bakhtegan were considered as the most resistant ones in both (vivo & vitro)
experiments. Reactions of the varieties to inoculation at the flowering stage were similar to
those at boll formation stage. Mean comparison of the data revealed significant differences
among all varieties, except the 3 most resistant ones mentioned above. Inoculation of young
plants at seedling stage did not show any disease symptoms.


Keywords


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