2015 Volume 81 Issue 1 Pages 32-42
Common scab of potato tuber caused by pathogenic Streptomyces species reduces vegetable quality and marketability, causing significant economic loss. In previous studies, quantitative real-time polymerase chain reactions (PCR) using primers designed based on the DNA sequence of pathogenicity island genes (e.g., txtAB, nec1) of pathogenic Streptomyces were developed. However, Streptomyces species vary in character, especially in their pH tolerance, so determining and quantifying the species is critical for developing effective control measures of scab. Here we developed a species-specific method to quantify Streptomyces spp. with an assay detection limit of about 200 fg of the target DNA. Cycle threshold (Ct) values were linearly correlated with the concentration of the target DNA (S. scabiei JK type: R2=0.9985, S. turgidiscabies: R2=0.9988) and were not affected by the presence of DNA from either species in plant tissues and soil. In this study, we developed new primer sets for real-time PCR to distinguish S. scabiei and S. turgidiscabies. By using these new primers and primers for txtAB, we also investigated the population dynamics of these species at different soil pHs (4.4, 4.7, 4.9, or 5.2 at planting), using SYBR Green quantitative real-time PCR. Potatoes were planted in bottomless frame pots with soil that had been amended with S. scabiei, S. turgidiscabies or both, then grown in the greenhouse. S. turgidiscabies tolerates lower soil pH than S. scabiei and grows well with a pH greater than 4.7. In all pots inoculated with the mix of S. scabiei and S. turgidiscabies, S. turgidiscabies always grew better and caused more severe root and scab lesions.
