Identification A New Pathogen Causing Potato Scab And Analysis Of The Toxin Synthetic Genes

Potato scab is mainly caused by plant pathogenic Streptomyces spp. It is distributed widely in the potato growing regions worldwide. The surface of the diseased potato becomes rugged after infection with Streptomyces spp. due to the toxins it produced and the quality of potato has decreased, causing economic losses. The disease happens in most of the potato growing regions and has aggravated year on year. In previous studies, we found a new strain of Streptomyces spp. that caused potato scab, named CPS-2. In this study, the biological characteristics and 16S rDNA test were used for the identification of the new strain. Analysis of the toxin synthetic genes was conducted by using southern hybrid test and PCR test.Pathogenicity test was carried out in greenhouse via pot inoculation test based on Koch's rule. The results showed that the new potatoes could represent typical scab symptom: bulge of the scab, suberinization of the cell, necrosis of hypoderm and hollow black spots after inoculated with CPS-2. The study also found pathgenicity of CPS-2 was stronger than S. scabies.Biology characteristic analysis and 16S rDNA sequence analysis were performed. The results included: gray colony, spiral spore hypha, cylindrical spore, smooth surface, size 1.401μm×0.893μm, produce melanin and H2S,minmal growth condition in acidity environment of pH 5.0, capable of utilizing fructose, arabinose, raffinose, rhamnose, sucrose, meso-inositol, glucose and xylose as the sole carbon source, grow on oxyproline, Methionine and Histidine as the sole nitrogen source, sensitive to phenol(0.1%) and Crystal violet(0.5μg/mL), tolerant to Penicillin(10 IU/mL), utilize starch and gelatine liquefication. The results correspond with the features of type strain of Streptomyces galilaeus. 16S rDNA analysis showed that the strain has 99.5% similarity with Streptomyces galilaeus. Therefore, the strain was categorized as Streptomyces galilaeus based on results of biology characteristic analysis and 16S rDNA sequence analysis.Primers were designed based on toxin synthetic genes(txtA,txtB,txtC and txtD)of potato scab pathogens described in published articles. txtA genes were amplified by PCR in strain CPS-2. Probe was made out of txtA sequence and hybrid with genome DNA of CPS-2 and the result of southern hybrid of txtA gene was positive. The results indicated that txtA exists in strain CPS-2.