Comparison in disease development and gas exchange rate of Pinus densiflora seedlings artificially inoculated with Bursaphelenchus xylophilus and B. mucronatus

Four-year-old seedlings of Pinus densiflora were inoculated with a suspension of B. xylophilus, or B. mucronatus adjusted to 3,000 nematodes per 50 μL sterilized distilled water in a greenhouse on July 21, 2008 to evaluate initial symptom development and the changes of gas exchange rate. B. xylophilus and B. mucronatus were distinguished by four restriction enzymes except Rsa I, and the result of ITS-RFLP of B. xylophilus used in this experiment was completely matched to that of pine wood nematode reported previously. Needle dehydration and subsequent yellowing were observed in all seedlings inoculated with B. xylophilus isolate while the appearance of the seedlings was normal in all seedlings inoculated with B. mucronatus and control. Needle dehydration was observed in most seedlings inoculated with B. xylophilus between 2 and 3 weeks after inoculation. In seedlings inoculated with B. xylophilus, continuous decrease in photosynthetic rate was observed after 6 days of inoculation. Photosynthetic rate decreased more markedly after 12 days of inoculation when external symptoms appeared in most seedlings, and ceased almost completely 19 days after inoculation. Photosynthetic decline in seedlings inoculated with B. mucronatus was only observed at 19 days after inoculation but recovered above control level after 25 days of inoculation. We found that disease development and the changes of gas exchange rate in the seedlings of Pinus densiflora inoculated with B. xylophilus were not observed on those inoculated with B. mucronatus.