10th U6+ Consortium of African Universities International Conference

Agroforestry practices have demonstrated a positive contribution towards soil fertility replenishment and soil conservation, climate change mitigation and adaptation and biodiversity preservation on agricultural land. However, little is still known about the disease and pest dynamics in these systems, including Plant parasitic nematodes (PPNs). The present study was carried out to characterize the PPNs community as affected by selected agroforestry tree species (Leucaena leucocephala, Calliandra calothyrsus, Sesbania sesban or Grevillea robusta) in Western Kenya. Soil samples were collected at an increasing radial distance (rhizosphere, canopy and open field) from the tree trunk of selected trees. Nematodes were extracted from the soil samples and morphologically identified to genera level. In total, ten genera of PPNs including Hoplolaimus, Helicotylenchus, Tylenchulus, Meloidogyne, Criconema, Rotylenchulus, Longidorus, Tricodorus, Xiphinema and Pratylenchus were identified. All the identified nematode genera in the present study encompass species of economic importance. Higher nematode densities of Helicotylenchus and Rotylenchus were recorded under G. robusta agroforestry systems at 20 individuals (100 cc soil)-1 and 55 individuals (100 cc soil)-1, respectively. C. calothyrsus agroforestry systems were dominated by Tylenchulus, Meloidogyne and Hoplolaimus nematodes. Helicotylenchus nematodes density decreased with increasing radial distance from L. leucocephala (18 individuals (100 cc soil)-1 in the rhizosphere and 3 individuals (100 cc soil)-1 in the open field), but increased with the increasing radial distance from C. calothyrsus, G. robusta and S. Sesban. Similarly, Meloidogyne density decreased with increasing distance from G. robusta (28 individuals (100 cc soil)-1 in the rhizosphere and 2 individuals (100 cc soil)-1 in the open field) only while it followed an opposite trend in the rest of the agroforestry systems. High population densities of Hoplolaimus, Meloidogyne, and Pratylenchus have been commonly associated with substantial yield decrease in maize-bean cropping systems of tropical Africa. The reported trends in the present study raise a concern about a potential phytosanitary risk when L. leucocephala and C. calothyrsus are planted at a high density in an agroforestry system, in Western Kenya.