Sub-Saharan Africa (SSA) is a region beset with challenges, not least its ability to feed itself. Low agricultural productivity, exploding populations, and escalating urbanization have led to declining per capita food availability. In order to reverse this trend, crop production systems must intensify, which brings with it an elevated threat from pests and diseases, including plant-parasitic nematodes. A holistic systems approach to pest management recognizes disciplinary integration. However, a critical under-representation of nematology expertise is a pivotal shortcoming, especially given the magnitude of the threat nematodes pose under more intensified systems. With more volatile climates, efficient use of water by healthy root systems is especially crucial. Within SSA, smallholder farming systems dominate the agricultural landscape, where a limited understanding of nematode problems prevails. This review provides a synopsis of current nematode challenges facing SSA and presents the opportunities to overcome current shortcomings, including a means to increase nematology capacity.

Potato cyst nematodes (PCN), such as Globodera rostochiensis and Globodera pallida, are quarantine restricted pests of potato causing major yield and financial losses to farmers. G. rostochiensis was first reported from Kenya’s key potato growing area in 2015. We sought to determine the diversity, prevalence and distribution of PCN species across the country by conducting a country-wide survey between 2016 and 2018, which included a more focused, follow-up assessment in three key potato growing counties. A total of 1,348 soil samples were collected from 20 potato growing counties. Information regarding local potato farming practices, potato cultivar use, their diversity and availability was also recorded. PCN cysts were obtained from 968 samples (71.8%) in all the counties surveyed, with Nyandarua County recording the highest PCN field-incidence at 47.6%. The majority of PCN populations, 99.9%, were identified as G. rostochiensis, while G. pallida was recovered from just one field, in a mixed population with G. rostochiensis. Inconsistencies in PCR amplification efficiency was observed for G. rostochiensis using the recommended EPPO primers, compared with ITS primers AB28/TW81, indicating that this protocol cannot be entirely relied upon to effectively detect PCN. Egg density in Nyandarua County varied between 30.6 and 158.5 viable eggs/g soil, with an average egg viability of 78.9 ± 2.8% (min = 11.6%, max = 99.9%). The PCN-susceptible potato cultivar named Shangi was the most preferred and used by 65% of farmers due to its shorter dormancy and cooking time, while imported cultivars (Destiny, Jelly, Manitou, and Markies) with resistance to G. rostochiensis were used by 7.5% of farmers due to unavailability and/or limited access to seeds. Thus, most farmers preferred using their own farm-saved seeds as opposed to purchasing certified seeds. Establishing the distribution and prevalence of PCN and elucidating the local farming practices that could promote the spread of PCN is a necessary precursor to the implementation of any containment or management strategy in the country and ultimately across the region.

The analysis of the functional diversity of soil nematodes requires detailed knowledge on theoretical aspects of the biodiversity–ecosystem functioning relationship in natural and managed terrestrial ecosystems. Basic approaches applied are reviewed, focusing on the impact and value of soil nematode diversity in crop production and on the most consistent external drivers affecting their stability. The role of nematode trophic guilds in two intensively cultivated crops are examined in more detail, as representative of agriculture from tropical/subtropical (banana) and temperate (apple) climates. The multiple facets of nematode network analysis, for management of multitrophic interactions and restoration purposes, represent complex tasks that require the integration of different interdisciplinary expertise. Understanding the evolutionary basis of nematode diversity at the field level, and its response to current changes, will help to explain the observed community shifts. Integrating approaches based on evolutionary biology, population genetics and ecology can quantify the contribution of nematode fauna to fundamental soil functions. These include carbon transformation, nutrient cycling, pest control and disease transmission. In conclusion, different facets of nematode diversity such as trophic groups, life history traits, variability in body size and/or taxa identities in combination with DNA-based techniques are needed in order to disclose nematode–soil–ecosystem functioning relationships. Further experimental studies are required to define locally adapted and sustainable management practices, through ecosystem-based approaches and nature-based solutions.

Mineral fertilizer application and consequent plant nutrition has long been observed to influence associated plant-parasitic nematode population densities, offering the potential as a nematode management option. Observations were made on the influence of mineral fertilizer application on nematode populations on three separate long-term rice experiments, (differential mineral application on upland and on lowland rice, and P application on upland rice) undertaken between 1994 and 1997 in Côte d'Ivoire. In 1995, on upland rice, treatments with K or N withheld from the comprehensive mineral application treatment (range of elements including N, P, K, Ca, Mg and Zn) led to lower densities of Pratylenchus zeae at harvest than the comprehensive mineral application. By withholding K or Mg, Helicotylenchus pseudorobustus densities were greater than with either the control (no mineral application) or comprehensive mineral application in the same year. No differences were observed between treatments in 1994, or between treatments for densities of other nematode species present (Meloidogyne incognita, Criconemella tescorum) or for total nematode density. In the lowland rice trial, no treatment effects on nematode species (Hirschmanniella oryzae and Uliginotylenchus palustris) were observed. In the P application trial on a P-deficient Ultisol, Heterodera sacchari densities were lower in treatments receiving 180 kg P ha⁻¹, than untreated in 1995; in 1996 no differences were observed between untreated and 135 kg P ha⁻¹, while in 1997 higher densities of H. sacchari were present in 135 kg P ha⁻¹ than untreated. Regression analysis of nematode densities against the mineral straw content in the P application trial revealed a negative correlation between M. incognita and Mn and Ca, and between P. zeae and Zn or Fe. A positive correlation was observed between Helicotylenchus spp. and Mg. This study provides strong arguments for taking plant parasitic nematodes into account when planning and executing long-term research trials.

The potato cyst nematodes (PCN) Globodera pallida and G. rostochiensis are key pests of potato, subject to strict quarantine regulations worldwide (EPPO, 2013a). Indigenous to South America, they have spread to numerous potato-growing regions around the world. G. rostochiensis, was reported from Kenya in 2015 (Mwangi et al. 2015). During a nationwide survey conducted in 2016, G. pallida was detected to occur in Kenya at an altitude of 2349 m above sea level in Nyandarua County (GPS “0.3150195, 36.48328”). Cysts were extracted from a 200 cm3 soil sample following EPPO diagnostic protocol (EPPO, 2013a), and then handpicked under a stereo microscope. The PCN recovered showed morphometric characteristics of G. pallida and is reported here. For further studies, the Nyandarua field was re-sampled in February 2017, to collected additional soil samples and confirm the occurrence of G. pallida. From the collected cysts, 10 cysts were inoculated on potato (Solanum tuberosum) ʻShangiʼ in pots with sterile soil and s...