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.

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Field trials were conducted in a plastic house artificially infested with an avirulent population of Meloidogyne javanica to determine the durability of the resistance mediated by the Mi gene in tomato rootstocks after repeated cultivation for three consecutive years. Treatments included an experimental rootstock cv. PG76 (Solanum lycopersicum · Solanum sp.), a commercial rootstock cv. Brigeor (S. lycopersicum · S. habrochaites), a resistant tomato cv. Monika (S. lycopersicum), and a susceptible cv. Durinta (S. lycopersicum). Based on the reproduction index (RI: number of eggs per g root on the resistant cultivar divided by number of eggs per g root on the susceptible cultivar · 100), rootstock cv. PG76 responded as highly resistant (RI ¼ 7%) after the first cropping cycle (3AE4 nematode generations), showed intermediated resistance (RI ¼ 33%) after the second cropping cycle (3AE3 generations), and was fully susceptible (RI ¼ 94%) after the third cycle (3AE3 generations). In contrast, rootstock cv. Brigeor and resistant cv. Monika retained intermediate resistance levels (RI ¼ 41 and 25%, respectively) after the third cropping cycle. Virulent nematode populations were rapidly selected from an avirulent one after repeated cultivation of resistant tomatoes under field conditions. Bioassays conducted under controlled conditions confirmed that selection for virulence occurred more rapidly in plots with cv. PG76 followed by Brigeor and Monika. The nematode population in the field not exposed to Mi resistance remained avirulent to Mi genotypes. The genetic background of the resistant rootstocks and the frequency of cropping were critical factors for the appearance of virulent nematode populations. Irrespective of nematode infection, all resistant tomatoes yielded more than the susceptible cultivar.

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