Occurrence of B ursaphelenchus mucronatus ( N ematoda: A phelenchoididae) and the microhabitat distribution of fungi in declining pine trees in a locale in K orea

A total of 33 pine trees with symptoms of decline were collected in J eonnam P rovince, S outh K orea, and were examined for the presence of nematodes. About 20% of the trees sampled were positive with B ursaphelenchus species. All B ursaphelenchus species were found in recently dead or dying trees. Based on morphological observations, the nematode extracted from the declining pine trees was identified as B . mucronatus . The highly pathogenic pine wood nematode B . xylophilus was not found in any pine trees sampled. B . mucronatus was easily reared on fungus B otrytis cinerea . Twenty one fungal isolates were isolated from dead trees, fallen twigs, and healthy pine trees. The fungal isolates belonged to T richoderma genus and were dominant in the wood of partially declining pines. The blue‐stain fungi transmitted by the M onochamus beetle were not detected. The B . mucronatus population decreased markedly on A uxarthron reticulatum   DY ‐2 isolated from soils. The number of nematodes also reduced on V erticillium saksenae   A ‐1, a nematophagous fungus, and B eauveria bassiana , an entomopathogenic fungus. This observation suggested the fungal production of nematicidal activity against B . mucronatus . When the fungal culture filtrates were also used for nematicidal activity on B . mucronatus , the culture filtrates of A ‐1, DY ‐2 and B . bassiana showed over 50% mortality within 48 h exposure. The fungi BC4 , BC5 and BC6 isolated from declining pine trees inhibited the reproduction of B . mucronatus , and their culture filtrates also expressed nematicidal activity, indicating a possible interaction between the fungi in pine trees and nematodes at microhabitat level.