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The occurrence of entomopathogenic nematodes (EPNs) in arable soil samples from Nigeria was investigated using Baermann extraction tray and insect-bait (White’s trap) techniques. Isolates were tested for infectivity using the larvae of Galleria mellonella (greater moth) and Tenebrio molitor (mealworm). The study revealed a new species of Heterorhabditis (MT371593) in soil samples that were randomly collected from an arable farmland cultivated with cassava TMS-30572 at the Teaching and Research Farm of Landmark University, Nigeria. Amplification of the internal transcribed spacer region (ITS) of the ribosomal DNA produced a nucleotide sequence of 933 base pairs (bp). A BLASTN search of GenBank showed that the sequence of the Nigerian isolate is identical at 99% similarity to that of Heterorhabditis sp. from Thailand. Infectivity test of the isolate showed 100% mortality against T. molitor larvae within 48 h of exposure while only 80% mortality was recorded for G. mellonella after 1 week of exposure. This is the first account of Heterorhabditis sp. in Nigeria. The varying degrees of infectivity against mealworm and greater moth observed in this study proved that the Nigerian isolate of Heterorhabditis sp. could potentially be an attractive option in the management of insect pests of cash crops.

Nutrients are being removed through pod harvest without replacement in the form of fertilizer application leaving the soil impoverished and the nutrients grossly inadequate for optimum cocoa yield. To address this issue, a randomised complete block designed study was carried out to examine the effects of readily available source of organic fertilizer like cocoa pod husks compost combined with mineral fertilizers on the yield of cocoa. The treatments with three replications consisted of Compost (100%), Compost (75%) + NPK (25%), Compost (50%) + NPK (50%), NPK (100%) and Control (no fertilizer). Results indicated that cocoa yield obtained with the compost plus NPK fertilization was significantly higher than with sole compost, NPK applications, and control in all locations. Percentage dry cocoa bean yield gain was 72.4% with the compost plus NPK fertilization, while sole compost or NPK alone was 36.4% compared to the control. Additionally, compost plus NPK fertilization significantly reduced black pod losses compared to sole compost, NPK, or control with percentage loss rate ranging from 9.9 to 13.4%, 21.6 to 23.1, 19.6 to 22.3, 32.2 to 35.5, respectively, in all locations. The use of CPH-based compost plus NPK fertilization has the potential to provide efficient integrated soil fertility restoration scheme that incorporated good agricultural practices and addressed disease management.

Low soil fertility, pests and diseases are major problems of growth and establishment of cacao seedlings on the field. Cocoa production increases by new plantings and rehabilitation of moribund farms, but a build-up of plant-parasitic nematodes (PPN) causing dieback and declining soil fertility has discouraged many farmers, leading to a reduction in crop productivity. In this study, the potentials of some organic wastes as fertilizers and their effects on establishment of cacao seedlings in PPN infected soils was investigated at Ibadan and Owena of Southwestern Nigeria. Goat dung (GD), organic fertilizer (OF), organo-mineral fertilizers (OMF) and NPK 15:15:15 were applied at 200, 400 and 600 kg ha-1, respectively, to cacao seedlings one month after transplanting, while unfertilized served as control. Results from the experiments showed a significant increase in percentage survival of cacao seedlings under organic fertilizers at Ibadan and Owena compared to NPK and control even at the lowest rate of 200 kg ha-1 3 years after transplanting. The incorporation of GD, OF and OMF significantly reduced the population densities of PPN compared to control. Therefore, GD, OF and OMF at 200 kg ha-1 are recommended for soil application to enhance the field establishment of cacao seedlings in the soil infected with PPN.

The genus Helicotylenchus contains cosmopolitan, ubiquitous plant-parasitic nematodes with some species capable of causing significant economic damage to agricultural crops. Accurate species identification in this genus is essential in recognizing the damaging species and establishing effective management options. In a study on cocoa plantations in Nigeria, two species of spiral nematodes were found in high numbers from soil samples obtained from a six-decade old cocoa plantation at the Cocoa Research Institute of Nigeria. An integrated approach involving a combination of morphology, morphometrics, and molecular tools was used to identify the nematode species. Morphological data indicate the presence of both H. multicinctus and H. dihystera. There is congruence in the morphological and molecular data obtained for H. multicinctus. However, phylogenetic analysis of the 28S rDNA expansion segment revealed a high variability in the sequences of the Nigerian population of H. dihystera, suggesting the need for a careful appraisal and more comparative studies.