• Journal of Korean Society of Forest Science
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• v.97 no.6
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• pp.570-575
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• 2008

This study was carried out to provide basic information on physiological changes of 4-year-old seedlings of Pinus thunbergii inoculated with pine wood nematodes by analyzing changes of symptom development, stem and needle water content and nematode populations in stem. Twenty days after inoculation, needles were discolored as an external symptom, and xylem drying and pith browning occurred at the above and below of the inoculation sites as an internal symptom. However, xylem drying began to occur 10 days after inoculation, which was determined by the difference in drying status of xylem and cortex between control and inoculated seedlings. Although population of pine wood nematode increased from 5 to 10 days after inoculation, it has increased dramatically from 10 to 20 days after inoculation when both internal and external symptoms appeared. As the time passed by after inoculation with pine wood nematodes, water content of stem and relative water content in current needles and branch gradually decreased. As the number of nematodes increases, water content of stem and relative water content of current needles and branches decreased significantly. There was a positive relationship between the number of nematodes and xylem drying and/or disease development, but the number of nematodes rapidly decreased as seedlings become severely diseased.

• The Plant Pathology Journal
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• v.25 no.3
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• pp.241-246
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• 2009

Korean pine (Pinus koraiensis Sieb. et Zucc.), a five-needle pine, has recently been suffering pine wilt disease caused by non-native pinewood nematode, Bursaphelenchus xylophilus. Three-year-old Korean pine seedlings were inoculated with 10,000 pathogenic nematodes in a greenhouse to investigate disease development, water content and the density of nematodes in stems. Needle dehydration, xylem drying and pith browning started 20 days after inoculation (DAI). There were significant differences between seedlings inoculated with nematodes and control seedlings in the relative water content of stems and leaves at 20 and 30 DAI. At 60 DAI, all remaining seedlings inoculated with nematodes had died, but control seedlings all remained alive. The average number of nematodes recovered from stems of Korean pine dramatically increased from 10 to 20 DAI, and then decreased at the end of the experiment at 60 days. This study suggests that the relative water content of stems and leaves in current-year branches could be used as a useful physiological indicator for early diagnosis of pine wilt disease.

• Korean Journal of Breeding Science
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• v.41 no.4
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• pp.377-384
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• 2009

Three-year-old seedlings of susceptible Pinus densiflora and resistant Pinus x rigitaeda were each inoculated with the pinewood nematode, Bursaphelenchus xylophilus, to compare disease development. Needle dehydration was evident on seedlings of P. densiflora by 20 days after inoculation, 10 days earlier than this symptom was observed on P. ${\times}$ rigitaeda. Xylem drying was more frequent in seedlings of P. densiflora than in that of P. ${\times}$ rigitaeda between 20 and 60 days after inoculation. No significant differences were found between P. densiflora and P. ${\times}$ rigitaeda for stem water content or for stem and leaf relative water content in current-year branches after nematode inoculation, but the average number of B. xylophilus recovered from stems differed significantly between the two groups. The number of B. xylophilus recovered from stems was negatively correlated with the stem water content and with stem and leaf relative water content. By the time the experiment was terminated at 60 days after inoculation, all 3 of the last group of P. densiflora seedlings had died, but 2 of the 3 remaining P. ${\times}$ rigitaeda hybrid seedlings were still alive. Additional studies are needed to further explore the specific mechanisms preventing nematode multiplication in the seedlings of resistant P. ${\times}$ rigitaeda.

• Research in Plant Disease
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• v.18 no.2
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• pp.101-108
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• 2012

In 2006, pinewood nematode, Bursaphelenchus xylophilus, was isolated from about 50 years old trees of Pinus densiflora and P. koraiensis showing leaf-wilt and -drying symptoms in Gwangju, Gyeonggi-do and Chuncheon, Gangwon-do. Isolation of pinewood nematodes from sapwood of infected pine trees showed no difference in population density between tree species and among the sampling heights on the main stem. Migration of pinewood nematodes in the host tree were investigated by inoculation of red pine (P. densiflora, 3 years old) seedlings with B. xylophilus. The nematodes seemed to move in red pine seedlings prior to multiplication and it might have taken about 20 days to start multiplication and expression of symptoms including wilt and dieback. In initial time after inoculation, nematodes started migration through the cortical resin canal from inoculated site and further showed upward and downward movements. More nematodes were observed in cortical resin canal during early period of inoculation and later in resin canal of xylem and tracheid also while, the pith still remained free from nematode. The density of B. xylophilus was higher in seedlings of low-vigor with poor root growth than in seedlings of normal root growth. Seedlings showing high density of B. xylophilus exhibited stem discoloration and secondary infection by fungus at the inoculation site.