In nature, plants are always under the threat of pests and diseases. Pathogenic bacteria are one of the major pathogen types to cause diseases in diverse plants, resulting in negative effects on plant growth and crop yield. Chemical bactericides and antibiotics have been used as major approaches for controlling bacterial plant diseases in the field or greenhouse. However, the appearance of resistant bacteria to common antibiotics and bactericides as well as their potential negative effects on environment and human health demands bacteriologists to develop alternative control agents. Bacteriophages, the viruses that can infect and kill only target bacteria very specifically, have been demonstrated as potential agents, which may have no negative effects on environment and human health. Many bacteriophages have been isolated against diverse plant-pathogenic bacteria, and many studies have shown to efficiently manage the disease development in both controlled and open conditions such as greenhouse and field. Moreover, the specificity of bacteriophages to certain bacterial species has been applied to develop detection tools for the diagnosis of plant-pathogenic bacteria. In this paper, we summarize the promising results from greenhouse or field experiments with bacteriophages to manage diseases caused by plant-pathogenic bacteria. In addition, we summarize the usage of bacteriophages for the specific detection of plant-pathogenic bacteria.

To date, fire blight, a bacterial disease in apple, pear and other Rosaceous plants, has been reported worldwide, while in Korea, this disease was not reported to date. In early May 2015, disease symptoms similar to typical blossom and shoot blight of fire blight disease were observed in young blossoms and shoots of Asian pear (Pyrus pyrifolia cv. ‘Shingo’) in 20 orchards in the regions of Anseong (37o00´30˝ N; 127o16´30˝ E) and Cheonan (36o48´55˝ N; 127o06´50˝ E). Disease incidence ((infected tree numbers/total tree numbers) x 100) varied from 0.2 to 93.2%. To isolate and identify the causal pathogen, 1 g of margins from healthy and diseased shoot was excised and homogenized in 1 ml of 10 mM MgCl2. The supernatant was spread on MGY (Mannitol Glutamic Yeast) medium and incubated at 26oC for 2 days. Based on colony morphologies, creamy white or white mucoid colonies were collected and purified. PCR with the universal primer set fD1/rP2 (Geider et al., 2008) for the partial 16 rRNA gene was performed, and t...

Carotenoids are essential for plant and animal nutrition, and are important factors in the variation of pigmentation in fruits, leaves, and flowers. Tomato is a model crop for studying the biology and biotechnology of fleshy fruits, particularly for understanding carotenoid biosynthesis. In commercial tomato cultivars and germplasms, visual phenotyping of the colors of ripe fruits can be done easily. However, subsequent analysis of metabolic profiling is necessary for hypothesizing genetic factors prior to performing time-consuming genetic analysis. We used high performance liquid chromatography (HPLC), employing a C₃₀ reverse-phase column, to efficiently resolve nine carotenoids and isomers of several carotenoids in yellow, orange, and red colored ripe tomatoes. High content of lycopene was detected in red tomatoes. The orange tomatoes contained three dominant carotenoids, namely δ-carotene, β-carotene, and prolycopene. The yellow tomatoes showed low levels of carotenoids compared to red or orange tomatoes. Based on the HPLC profiles, genes responsible for overproducing δ-carotene and prolycopene were described as lycopene ε-cyclase and carotenoid isomerase, respectively. Subsequent genetic analysis using DNA markers for segregating population and germplasms were conducted to confirm the hypothesis. This study establishes the usefulness of metabolic profiling for inferring the genetic determinants of fruit color.

Diverse plant pathogens secrete cellulases to degrade plant cell walls. Previously, the plasmid-borne cellulase gene celA was shown to be important for the virulence of the gram-positive bacterium Clavibacter michiganensis in tomato. However, details of the contribution of cellulases to the development of wilting in tomato have not been well-determined. To better understand the contribution of cellulases to the virulence of C. michiganensis in tomato, a mutant lacking cellulase activity was generated and complemented with truncated forms of certain cellulase genes, and virulence of those strain was examined. A celA mutant of the C. michiganensis type strain LMG7333 lost its cellulase activity and almost all its ability to cause wilting in tomato. The cellulase catalytic domain and cellulose-binding domain of CelA together were sufficient for both cellulase activity and the development of wilting in tomato. However, the expansin domain did not affect virulence or cellulase activity. The celA ortholog of Clavibacter sepedonicus restored the full virulence of the celA mutant of C. michiganensis. Another cellulase gene, celB, located in the chromosome, carries a single-base deletion in most C. michiganensis strains but does not carry a functional signal peptide in its N terminus. Nevertheless, an experimentally modified CelB protein with a CelA signal peptide was secreted and able to cause wilting in tomato. These results indicate that cellulases are major virulence factors of C. michiganensis that causes wilting in tomato. Furthermore, there are natural variations among cellulase genes directly affecting their function.

Bacteriophages, bacteria-infecting viruses, have been recently reconsidered as a biological control tool for preventing bacterial pathogens. Erwinia amylovora and E. pyrifoliae cause fire blight and black shoot blight disease in apple and pear, respectively. In this study, the bacteriophage phiEaP-8 was isolated from apple orchard soil and could efficiently and specifically kill both E. amylovora and E. pyrifoliae. This bacteriophage belongs to the Podoviridae family. Whole genome analysis revealed that phiEaP-8 carries a 75,929 bp genomic DNA with 78 coding sequences and 5 tRNA genes. Genome comparison showed that phiEaP-8 has only 85% identity to known bacteriophages at the DNA level. PhiEaP-8 retained lytic activity up to 50°C, within a pH range from 5 to 10, and under 365 nm UV light. Based on these characteristics, the bacteriophage phiEaP-8 is novel and carries potential to control both E. amylovora and E. pyrifoliae in apple and pear.