This chapter has examined how climate change is reshaping plant pathogen epidemiology, moving from the climatic drivers of change to their consequences for pathogen distribution, disease emergence and crop protection. Temperature, precipitation and humidity, atmospheric carbon dioxide and extreme weather each influence the host, the pathogen and the environment, and their effects interact rather than simply add up. The classical disease triangle is therefore not only shifting; the zone in which disease is favoured is widening.
The evidence for this is no longer hypothetical. The six cases reviewed here, namely wheat stem rust Ug99, cassava mosaic disease and its whitefly vector, banana Fusarium wilt TR4, wheat blast, maize lethal necrosis and coffee leaf rust, differ in pathogen type, host and mechanism, yet they point to the same conclusion: pathogens and vectors are establishing themselves far beyond their historical ranges, and new disease complexes are forming from organisms that were previously minor problems. Compound stresses, illustrated by the flood drought–disease sequence of Nigeria’s 2022 season, can produce losses well beyond those expected from any single stress. Disease outcomes under such conditions are also context dependent, as the variable effects of drought showed.
At the same time, detection and response capacity has not kept pace. Surveillance in sub–Saharan Africa is sparse, new pathogens may spread widely before they are formally confirmed, and many predictive models rest on data from other regions. Forecasting, risk-based surveys and AI-assisted diagnostics such as PlantVillage Nuru can create valuable lead time, but they are necessary rather than sufficient. Without resistant germplasm, effective quarantine and sound crop management, early warning will only delay losses, not prevent them.
For Nigeria and the wider African continent, where many of the most damaging cases are concentrated and where the capacity to absorb climate-driven crop losses remains limited, the central lesson is that the epidemiological baseline is a moving target. Crop protection must therefore become adaptive, anticipating where disease will be favoured next rather than responding only where it has already occurred.
Recommendations
Considering the above trends, the following recommendations are proffered:
i. Direct surveillance towards regions of anticipated risk: Surveillance investment should shift from historically known outbreak centres to areas where climatic suitability and host presence indicate that introduction is eminent.
ii. Plan resistance breeding around emerging threats: Breeding programmes should target pathogens likely to arrive, not only those currently endemic. The loss of Sr31 protection to Ug99, and the emergence of maize lethal necrosis from viruses that were individually mild, show that long-standing resistance can fail quickly. Resistance to threats such as cassava brown streak disease should be incorporated before the disease reaches a given region, and breeding for flood and climate-stress tolerance should be prioritised.
iii. Strengthen quarantine and phytosanitary cooperation: Because soil-borne pathogens such as banana Fusarium wilt TR4 cannot practically be eradicated once established, prevention must be the priority. This requires clean planting material, management of soil and farm machinery, and coordinated cross-border quarantine. Regional training of plant protection officials, such as the FAO initiative involving Nigeria and other African countries, should be sustained on a precautionary basis.
iv. Develop regionally calibrated forecasting models: Predictive models should be built and validated with West African epidemiological and climatic data so that they reflect local pathogens, crops and cropping systems, instead of relying on models trained elsewhere.
v. Deploy digital and AI tools alongside ground verification: Tools such as PlantVillage Nuru should be extended to extension agents and farmers to widen diagnostic reach, particularly where laboratory access is limited. Their outputs should be checked by trained plant pathologists and laboratory confirmation, since such tools complement and do not replace expert diagnosis.
vi. Build compound-stress early warning and management systems: Flood early warning systems, together with drought and flood management, should be integrated with pest and disease monitoring so that post-flood and post-drought disease pressure can be anticipated, as the 2022 experience in Nigeria shows.
vii. Invest in institutional capacity: National plant protection organisations, diagnostic laboratories and research institutions need sustained funding and trained personnel so that new pathogens can be identified and characterised promptly, before they spread widely.
SAEREM 2026 OCTOBER BOOK CHAPTER NEW.docxChapter Chapter Two
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