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Limited and fragmented information is available about the effects of conservation agriculture, increasingly adopted by grain producers in sub-Saharan African countries, on nematode assemblages in maize-based cropping systems. Rhizosphere samples were obtained from three treatments, viz. conservation (CA) and conventional maize (CTA) fields, as well as from natural veld (NV) areas (serving as the reference) adjacent to maize fields in South African production areas. Forty-nine nematode genera (12 plant-parasitic and 37 non-parasitic/beneficial) were identified. Prominence values (PV) showed that Rotylenchulus and Meloidogyne (in descending order) dominated in 50 g roots of all three treatments, Pratylenchus in 5 g roots, and Rotylenchulus and Scutellonema in 200 g soils from CA and CTA maize, as opposed to Helicotylenchus and Rotylenchulus in soils from NV. Pratylenchus abundance in 5 g roots was significantly higher in CA and CTA maize compared to NV, with the Shannon diversity index values (H') also being the highest for species of this genus in CA, followed by CTA and NV. Rotylenchulus abundance/50 g roots was significantly higher in CA compared to both CTA and NV, while Meloidogyne abundance/50 g roots did not differ significantly among the three treatments. For soil nematodes, the H' was highest for NV, but not significantly compared to CA and CTA. Ninety-one percent of beneficial nematode genera and families were associated with NV soils, generally with higher PV and significant higher abundance (for bacterivores and predators) and diversity (for bacterivores, omnivores and predators) compared to CA and CTA. Nonetheless, most soils from the three treatments represented resource-depleted soil nematode communities indicating that soil health should be improved by using strategies such as cover cropping, incorporation of organic materials and inclusion of crop rotation sequences using cultivars with poor-host status or resistance to the dominating, target plant-parasitic nematode species to enable sustainable crop production. Associations of nematode assemblages, plant-parasitic and beneficial, with selected soil properties are also illustrated. [ABSTRACT FROM AUTHOR]

Entomopathogenic nematodes (EPNs) are microscopic roundworms that are found in soil worldwide. They deliver an important ecosystem service through preventing natural flares in insect reproduction by means of utilising the soil stages of insects as a food source and by acting as natural biocontrol agents. A survey of EPNs was conducted in the JS Marais Nature Reserve, Stellenbosch, in the Western Cape province of South Africa. Soil samples were baited with the larvae of three susceptible hosts, codling moth (Cydia pomonella), wax moth (Galleria mellonella) and mealworm (Tenebrio molitor) to determine the presence of EPN. Of the 76 soil samples collected across the reserve, 39 were found to be positive for the presence of EPN (51.32%). Among the positive samples, 87% contained Steinernema isolates, 8% contained Heterorhabditis and 5% contained the Oscheius sp. Morphological and molecular studies were performed to characterise the isolates to species level. The Steinernema species were identified as Steinernema khoisanae in 34 samples, and as Steinernema nguyeni in five samples. The only species of Heterorhabditis found was H. safricana, which was identified from three samples. An unknown Oscheius sp. was found in two samples. The reserve’s population of S. khoisanae showed interesting inter-individual variation (93%) early in the internal transcribe spacer (ITS) region, leading to short single-usable sequences, which, in most cases, included only the ITS1 or ITS2 region. However, using the D2D3 confirmed their identity as S. khoisanae, with such occurring in all areas and soil types of the reserve. Conservation implications: The undisturbed alluvial fynbos and renosterveld of the JS Marais Nature Reserve showed high EPN abundance and diversity in stark contrast to the agro-ecosystems present in the Cape floristic region. This finding, on a micro level, should be conserved for future bioprospecting in the fynbos for EPNs with potential as biocontrol agents.

No abstract available.