Submitted to: Nematologia Mediterranea
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2008
Publication Date: 6/30/2008
Citation: Khan, A., Sayed, M., Shaukat, S., Handoo, Z.A. 2008. Efficacy of four plant extracts on nematodes associated with papaya in Sindh, Pakistan. Nematologia Mediterranea. 36:93-98. Interpretive Summary: Plant-parasitic nematodes are microscopic worms that cause global crop losses exceeding $100 billion annually. These losses will increase because the most widely used chemical pesticide used to kill nematodes is being prohibited from use. One approach to solving the problem of designing new, safe means of controlling nematodes is through the treatment of soil nematode populations with plant extracts. In the present study, ARS and University of Karachi scientists evaluated extracts of four plant species (neem, ashwagandha, marigold, and eucalyptus) in field and pot experiments to determine if they could reduce population levels of plant-parasitic nematodes, including the root-knot nematode, the most economically important nematode infecting papaya in Pakistan. The scientists discovered that root-knot nematode populations were remarkably reduced by all the treatments, as were populations of other nematode species associated with papaya. These results are significant because they provide the first indication that the use of these plant extracts for the management of papaya nematode populations is effective and would be expected to be more environmentally friendly than synthetic nematicides. This research will be used by scientists developing new methods for safely controlling nematode-induced crop losses.
Technical Abstract: This investigation examines the effect of ethanol extracts of four plant species--Azadirachta indica (neem), Withania somnifera (ashwagandha), Tagetes erecta (marigold) and Eucalyptus citriodora (eucalyptus)--against nematodes associated with papaya (Carica papaya), and it assesses their influence on plant growth and fruit yield. Although fresh shoot weight of papaya seedlings in pot experiments was significantly increased by the plant extracts, fresh root weight generally remained unaltered compared to the controls. The number of Meloidogyne incognita juveniles, gall index, and the number of egg masses per root were remarkably reduced by all the treatments. The population densities of M. incognita, Helicotylenchus multicinctus and Hoplolaimus indicus, the major nematode species associated with papaya, were significantly reduced in the field by all four plant extracts. M. incognita and H. multicinctus were the most affected by Withania, whereas H. indicus was reduced the greatest by Tagetes extracts. Papaya yield was increased by the treatments in the following order from largest to smallest: Withania somnifera, carbofuran, Azadirachta indica, Tagetes erecta, and Eucalyptus citriodora. The possible mechanisms of the nematicidal effects of the plant extracts are discussed.