Diversity of phyto-parasitic nematodes in the on-farm cocoa (Theobroma cacao L.) plantations of south western Nigeria

Abstract

Parasitic nematodes have evident contribution to the yield loss of cocoa in south western Nigeria, a region which accounts for the highest cocoa production of Nigeria. Research to identify types, population and frequency of occurrence of different nematode genera around the rhizosphere of cocoa in Nigeria has been poorly attempted. However, information on the biodiversity of each significant nematode species is critical for initiation of an efficient control programme. Therefore, to ascertain this critical information, soil samples were collected from 45 farms in three south western states of Nigeria. With the modified Baerman Funnel method, a total of 12 phyto-parasitic nematode taxa were extracted from the soil samples. Seventy-five percent of the extracted nematodes belong to the migratory class. Meloidogyne spp occurred in the highest abundance (79.83) and frequency (97.7%). Other genera with higher population densities were: Tylenchus, Helicotylenchus, Pratylenchus and Rotylenchus in the respective abundances of 35.2, 31.7, 30.3 and 23.9, with frequencies ranging between 65 - 77%. Cocoa trees host large populations of phyto-parasitic nematodes, the proportion of each genera is highly diverse; varying between farms, locations and states. A thorough investigation of individual nematode pathogenicity is necessary. Furthermore, their interactions within the rhizosphere and their contributory role to lowering cocoa productivity in farmer fields in Nigeria would be an informative guide to controlling them.