Nematodes, an Emerging Threat to Global Forests: Assessment and Management

Nematode infestation in forest trees has been a neglected area of research apparently due to non appearance of visible symptoms and difficulty of accessibility to the sampling sites for damage assessment. High organic content, adequate moisture and moderate temperature of forest soils with diversified flora represent conducive condition for nematode survival in forest habitats. Limited investigations so far conducted have revealed infestation of important forest trees such as acacia, sal, teak, pine and sandal wood with Helicotylenchus, Tylenchorhynchus, Hemicriconemoides, Macroposthonia, Pratylenchus, Meloidogyne, Xiphinema, Trichodorus and Paratrichodorus etc. Nematode damage to forest trees usually appears as a slow decline of growth which gradually gets aggravated leading to tree death within 5 to 10 years. However, some nematodes such as pine wilt nematode (Bursaphelenchus xylophilus) and foliar nematode (Subanguina chilensis) cause wilting, drying and defoliation of a branch or the entire tree within a year. The legal or illegal export/import of unprocessed timber and wood in Asia especially from risk prone countries such as China, Nepal and Bhutan has posed a serious quarantine risk of spread of this nematode in to India, Pakistan, Afghanistan, Iran and other countries having favorable climate for the nematode and its insect vector. With this paper an effort is made to highlight the threat of nematode infestation to the global forests and possible options available for their management.