Isolation, identification, and pathogenicity of Lelliottia amnigena causing soft rot of potato tuber in China.

Potato (Solanum tuberosum L.) is regarded as the fourth most important food crop because of its economic and nutritional benefits. This crop suffers significant annual losses due to a variety of phytopathogens. Bacterial soft rot disease is one of the most serious diseases that cause significant losses in potato yield all over the world. Therefore, identification of a soft rot pathogen is critical for easy control, as each pathogen has distinct ways of being controlled. Lelliottia amnigena is a subgroup of the genus Enterobacter with many species associated with crop plants, making its classification difficult and complex. Therefore, this study focused on the isolation and identification of a newly L. amnigena from rotten potato tuber obtained from the field after harvest, Lanzhou City, China. Four strains designated as PC2, PC3, PC4 and PC5 were isolated from the same rotting potato tuber. Pathogenicity test showed that strain PC3 induced soft rot symptoms on healthy potato tubers. Koch's postulates were confirmed by re-isolating the strain PC3 in the inoculated tubers. Strain PC3 showed a convex, oval and smooth colony, measuring 0.9-1.3 1.8-3.6 µm under the microscopic observation. Phylogenetic analysis based on 16S rRNA, rpoB and atpD genes showed that strain PC3 species was 99.44%, 97.24%, and 100%, closely related to L. amnigena with accession numbers 240-a-etp (MN208158.1), FDAARGOS (CP023529.1) and R-6 (MN658356.1), respectively. The bacterial strain (PC3) was deposited in the Genbank with the accession number SUB10508072 PC3 OK447935. To the best of our knowledge, this is the first report of L. amnigena causing soft rot on potato tubers in China.

Potential of an endophytic bacteria Bacillus amyloliquefaciens 3-5 as biocontrol agent against potato scab.

To obtain a potential biocontrol agent for potato scab, 75 endophytic bacteria were isolated from the healthy potato tubers and strain 3-5 was selected as an optimal antagonistic bacterium against Streptomyces griseoplanus (Streptacidiphilus griseoplanus) causing potato scab. Strain 3-5 was identified as Bacillus amyloliquefaciens based on its morphological characteristics, 16S rDNA and gyrB gene sequence analysis. B. amyloliquefaciens 3-5 has biological functions of indole-3-acetic acid (IAA) production and nitrogen fixation. Polymerase chain reaction (PCR) detection revealed that B. amyloliquefaciens 3-5 had 6 diverse antibacterial substance synthesis genes, named bacD, bacAB, ituD, ituC, sfP and albF, which resulted in the production of bacilysin, iturin, surfactin and subtilosin. Field efficacy evaluation revealed that B. amyloliquefaciens 3-5 (solid fermentation) was successful in controlling potato scab with a 38.90 ± 3.2140% efficiency which is higher than other chemical bactericides except zhongshengmycin·oligosaccharins and kasugamycin·zhongshengmycin. The endophytic bacterium B. amyloliquefaciens 3-5 could be used as a biocontrol agent against potato scab due its control efficacy and environmental safety.

Identification and biological characterization of a new pathogen that causes potato scab in Gansu Province, China.

Potato scab caused by pathogenic Streptomyces is a serious soil-borne disease on potato. In this study, a new Streptomyces strain 5A-1 was isolated from potato samples in China. Based on morphological characteristics, 16S rDNA gene sequence analyses, it was identified as Streptomyces griseoplanus (Streptacidiphilus griseoplanus), pathogenicity of which was measured by the methods of small potato chips, radish slices and potato pot trial inoculation. Moreover, the pathogenic genes txtAB and tomA from the Streptomyces pathogenicity island (PAI) were detected. Determination of biological characteristics showed that the optimal temperature for the growth of S. griseoplanus strain 5A-1 was 25 °C, the optimal light condition was darkness, the optimal pH value was 8.5 and the most preferred carbon source and nitrogen source is glucose and aspartate, respectively. To our knowledge, it is the first report for S. griseoplanus, as a new pathogen, to cause potato scab.