Specific and Sensitive Detection of Enterobacter mori Using Reliable RT-PCR.

Enterobacter mori, the causal agent of bacterial wilt in mulberry, is becoming a serious disease in mulberry orchards in China. Because no effective control strategy has been devised for this disease, the reliable screening of mulberry material for latent infection became necessary. Hence, a fast polymerase chain reaction (PCR) assay for the detection of E. mori was developed in this study. The primers were designed within regions of the RNA polymerase ß-subunit (rpoB) gene. The method is fast and simple and showed 100% sensitivity (no false negatives) and 100% specificity (no false positives), which was tested with 4 representative E. mori strains, 9 Enterobacter type strains, 2 strains of the other major mulberry bacterial pathogens (Ralstonia solanacearum and Pseudomonas syringae pv. mori) in China, 7 strains of other plant-associated pathogens, and 50 unidentified epiphytic bacterial isolates from mulberry plants. The real-time PCR assays reliably detected the DNA at at least 10 fg/µl and the bacterial cells at 102 CFU/ml from mulberry shoots and roots suspension. The strong positive reaction in testing of all symptomatic plants (with 100% positive) and parts of asymptomatic latent infected plant samples (with 36.4% positive) provided proof that this method is reliable and sensitive and suitable for screening plant material with latent infections of E. mori.

Isolation and characterization of antagonistic bacteria against bacterial leaf spot of Euphorbia pulcherrima.

AIMS: To investigate the inhibition potential of leaf-associated bacteria against the pathogen of bacterial leaf spot of Euphorbia pulcherrima. METHODS AND RESULTS: Seven out of 200 bacterial strains were effective antagonists by in vitro screening and the two strains PAB241 and PAB242 significantly reduced the disease incidence and severity as foliar treatments of E. pulcherrima. The two effective strains, PAB241 and PAB242, were both identified as Bacillus amyloliquefaciens by a polyphasic approach including phenotypic feature, carbon source utilization profile, fatty acid methyl esters and analysis of 16S rRNA gene sequence. In addition, the suspensions of B. amyloliquefaciens PAB241 and PAB242 showed antibacterial activities against the pathogen of bacterial leaf spot of E. pulcherrima under different treatments. CONCLUSIONS: The leaf-associated bacteria, B. amyloliquefaciens PAB241 and PAB242, markedly inhibited the growth of X. axonopodis pv. poinsettiicola under different treatments and protected E. pulcherrima from pathogen infection in growth chamber conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study that showed B. amyloliquefaciens from plant leaves was a potential bactericide against bacterial leaf spot of E. pulcherrima.