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IntroductionCamellia japonica is a broad-leaf evergreen tree that is naturally distributed in coastal areas of the southern parts of Korea (Park et al., 2017). This tree constitutes an important type of coastal vegetation in Korea because the tree is relatively tolerant to sea breeze and salinity. However, most C. japonica forests in the coastal areas of Korea have been degraded due to human activities such as road construction, urban development, and seedling collections for potted planting. The Korean government has made efforts to restore C. japonica forests in coastal areas, but restoration is very difficult (Park et al., 2017). In coastal environments, plant growth and survival are affected by the salinity of the soil and by the low availability of nutrients (Williams et al., 1998;Weber and D' Antonio, 1999). In particular, excess salt in the soil can decrease plant growth by inhibiting the osmotic uptake of water by roots or by causing nutritional imbalance through competitive ion absorption (Koyro, 2006).Plant growth-promoting rhizobacteria (PGPR) are the rhizosphere bacteria that can enhance plant growth by a wide variety of mechanisms including phosphate solubilization, siderophore production, biological nitrogen fixation, rhizosphere engineering, phytohormone production, and interference with pathogen toxin production. The potentiality of PGPR in agriculture and forestry is steadily increased as it offers an attractive way to replace the use of chemical fertilizers, pesticides, and other supplements (

Pine wilt disease (PWD) caused by pine wood nematode, Bursaphelenchus xylophilus, has become the most serious threat to pine trees in Korea. This study was subjected to investigate effective biological control agent against PWD. To select nematocidal bacteria against PWD, Bacillus licheniformis MH48 was selected among five bacteria due to its high nematocidal potential. B. licheniformis MH48 was tested for cell growth and protease activity to evaluate its nematicidal potential. In the B. licheniformis MH48, cell numbers were highest three days after incubation, while protease activity was highest after seven days. In the effect of different concentrations of B. licheniformis MH48 culture broth against B. xylophilus, 20% concentration of culture broth showed approximately 80% of pine wood nematode mortality compared to the control. Especially, pine wood nematode's cuticle layers were degraded two days after treatment of B. licheniformis MH48 culture broth. The present study suggests that B. licheniformis MH48 can be one of the potential biocontrol candidates against pine wood nematode due to its ability to produce protease.