Robigalia Roundup LXXVII: Anniversary of Robigalia

Few tropical plant pathogens are as destructive, or as versatile, as Phytophthora palmivora. Despite often being lumped in with “fungal diseases,” it is not a true fungus but an oomycete, a water mould, and one with a host range of more than 200 plant species across the tropics.

It is best known as a major cause of black pod on cacao, but it also attacks coconut, papaya, rubber, black pepper, durian, and many other economically important crops.

Phytophthora palmivora is a hemibiotroph, meaning it begins infection in living tissue before later colonising dead or dying tissue. Its life cycle is tightly linked to moisture: it produces motile zoospores that swim in free water, encyst on plant surfaces, germinate, and form appressoria to penetrate host tissue.

Once inside, it can develop intracellular feeding structures and rapidly transition from early colonisation to aggressive rot, which is one reason outbreaks escalate so quickly under wet tropical conditions.

On cacao, P. palmivora causes black pod disease, one of the most economically important diseases in cocoa production worldwide. Infected pods develop brown lesions that quickly expand, darken, and can engulf the entire pod, often leaving it blackened and rotting on the tree.

The same pathogen can also cause stem cankers and infect a wide range of other tropical hosts, where symptoms include fruit rots, bud rots, collar rots, leaf lesions, and seedling blight depending on the crop and tissue infected.

Geographically, P. palmivora has a pantropical distribution and occurs in virtually all major cocoa-growing regions. Its success comes partly from that broad host range and partly from how efficiently it spreads in humid environments, with inoculum moved by rain splash, contaminated soil, infected planting material, and sometimes insects or tools. In practical terms, this makes it both a production problem and an ongoing biosecurity concern for tropical and subtropical agriculture.

Management depends on integration rather than any single fix. Good drainage, wider spacing, pruning to improve airflow, sanitation through removal of infected pods or plant material, use of tolerant varieties, and careful nursery hygiene all help reduce disease pressure, while chemical control often relies on copper-based products or phosphonate-type treatments where appropriate.

As with many Phytophthora diseases, the real challenge is that once warm, wet conditions arrive, the pathogen already has everything it needs to move fast.

Keeping reading to learn more about Phytophthora palmivora and meet a PhD candidate investigating potential biocontrol agents.

Paola Moreno López is a PhD candidate in Agricultural Sciences at the University of Cundinamarca in Colombia, whose career reflects a steady and purposeful deepening of her commitment to plant health and sustainable crop production.

She began her academic journey as an Agricultural Engineer before completing a Master of Agricultural Sciences with a specialisation in plant pathology. These foundations gave her both the field-level perspective of a practising agronomist and the diagnostic rigour of a research scientist, a combination that has defined her approach ever since.

From early in her studies, she was drawn to the practical weight of the discipline, recognising that disease management sits at the heart of food security for farming communities across Colombia and beyond.

At the University of Cundinamarca, Paola has worked as both a lecturer and researcher, contributing to projects focused on plant health, integrated disease management, and the sustainability of agricultural production systems.

Her dual role has allowed her to bridge the gap between scientific investigation and the next generation of agronomists, and she counts the success of her students among her proudest professional achievements.

Her doctoral research brings these threads together with a focus on cacao. She is currently investigating fungal agents with biocontrol potential and examining the transcriptomic changes that occur in cacao plants when the host, biocontrol fungi, and the pathogen Phytophthora palmivora are present simultaneously. This work has direct relevance for reducing chemical inputs and supporting smallholder producers.

Connect with Paola on LinkedIn to discuss biocontrol strategies, Phytophthora in cacao, and integrated disease management in tropical cropping systems.

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P.S. Why Robigalia? The name originates from the Ancient Roman festival dedicated to crop protection. You can read all about the history here: