Production of thaxtomin a by two species ofStreptomyces causing potato scab |
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Authors: | El-S A El-Sayed |
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Institution: | (1) Department of Botany, Faculty of Science, Zagazig University, Zagazig, Egypt |
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Abstract: | A total of nine isolates of streptomycetes were isolated from scab lesions on potato tubers. Five of nine isolates were pathogenic
on potato minitubers. Four of the pathogenic isolates produced thaxtomin A (ThxA) in infected tuber tissues. The lesion surface
areas inducing ThxA were highest in treatment of the minitubers with an extract of OMB inoculated with S-66 and S-67, intermediate
with that inoculated with S-64 and lowest with S-63. The pathogenic isolates were identified by gray aerial mycelia, melanin
pigment productivity, the type of spore chain morphology and carbon utilization asS. scabies strains S-63, S-64 and S-68, andS. acidiscabies strains S-66 and S-67. Strains S-63 and S-64 produced 0.65 and 1.60 mg ThxA per L of OMB, respectively, strains S-66 and
S-67 producing similar amounts,viz. 2.36 and 2.10 mg/L, respectively. The optimal temperature for production (by both species) was 28 °C. Production of ThxA
byS. scabies strain S-64 andS. acidiscabies strain S-66 was suppressed at least 50-fold at 0.5 and 0.3 % of glucose, respectively. Fructose enhanced the production by
both species. |
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