Abstract
Streptomyces scabies (Thaxter) causes destructive and serious damages to many vegetable field crops, including potato. Fourteen pure isolates were obtained from naturally diseased potato tubers showing symptoms of common scab disease, collected from different localities of Sohag governorate, Egypt. All tested isolates were identified as S. scabies (Stc) according to morphological and biochemical tests. Isolate Stc 10 exhibited the highest activity of polyphenoloxidase enzyme, followed by isolate Stc 11, while isolate Stc 2 produced the lowest activity of this enzyme. Concerning the peroxidase activity, the isolates varied in their production; Stc 11 exhibited the highest activity enzyme, followed by isolate Stc 2, whereas isolate Stc 10 produced the lowest activity of enzyme. In regard with Tyrosine Amonnia Lyase (TAL) activity, isolate Stc 2 exhibited the highest activity, followed by isolate Stc 10, whereas isolate Stc 11 exhibited the lowest activity. Agarose gel electrophoresis of the PCR amplification products revealed a band representing the expected 279 bp DNA fragment in each DNA extracted from the highly pathogenic isolates Stc 10 and 11. The results demonstrated that PCR amplification of the nec1 gene could be used as a reliable marker for detecting pathogenic Streptomyces isolates on potato tubers.
Highlights
There are many diseases that attack potato in the field crop among which common scab is one of the bacterial diseases that register high economic loses
On the basis of morphological, cultural, physiological and pathological characteristics of the isolated bacteria, it was concluded that all tested isolates could be identified as Streptomyces scabies
Results indicated that isolate Stc 10 exhibited the highest activity of polyphenoloxidase enzyme, followed by isolate Stc 11, whereas isolate Stc 2 showed the lowest activity of enzyme
Summary
There are many diseases that attack potato in the field crop among which common scab is one of the bacterial diseases that register high economic loses. Streptomyces scabies) is the main causal agent of common scab, a widely-distributed disease that causes important economic wastes in potato production (Lambert and Loria, 1989; Goyer et al, 1996). The nec gene encodes a secreted necrogenic protein with an uncharacterized plant cell target and was shown to confer a pathogenic phenotype on the nonpathogenic Streptomyces lividans (Bukhalid et al, 1998). The nec gene is structurally and functionally conserved among unrelated pathogenic Streptomyces species and absent in nonpathogens from a wide geographic origin (Bukhalid et al, 2002; Park et al, 2003). There exists a strong correlation between thaxtomin A production and the presence of nec in pathogenic strains of S. scabies, S. acidiscabies and S. turgidiscabies (Bukhalid et al, 1998). The nec protein is not required for thaxtomin production and it represents an independent virulence factor (Kers et al, 2005)
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