Pest and disease threat to neem: What lessons must be learnt for tree improvement programmes?

摘要

Development initiatives and programmes aimed at local farmers now routinely embrace a broad range of (non-industrial) tree species in addition to annual crops, the more traditional focus of attention. Tree improvement has been a particularly attractive area of interest, given the limited exploitation of non-industrial trees in the past and their emerging importance. Such improvement programmes address a wide range of biological issues, yet have mostly ignored pests and diseases, unlike similar work on annual crops. It is often assumed that tree pests and diseases only become a problem when they are widely noticeable, yet this ignores stubborn problems relating to accurate assessment and diagnosis. This approach also fails to take account of major gaps in our knowledge of diseases and health problems affecting non-industrial tree species. The emergence of neem decline in Niger and Nigeria in 1990, and scale attack by Aonidiella orientalis in Cameroon and Nigeria in the 1980s, illustrates some of the dangers and difficulties in dealing with new outbreaks, while also emphasizing strategic research issues which need to be addressed routinely by tree-improvement programmes. I will be drawing similar points from a consideration of the leucaena psyllid (Heteropsylla cubana, an insect pest) and Gliricidia sepium (little leaf and virus-like diseases), two trees which have also been the subject of major genetic resource initiatives in recent years. In marked contrast to industrial tree improvement programmes, exemplified by commercial forestry involving eucalypts in Brazil and South Africa and Pinus radiata in New Zealand, there is little or no routine consideration of pests and diseases of non-industrial trees. This-needs more careful consideration if we are to avoid shortsighted policies which threaten the security of production and success of new introductions.