Cocoa plants get protection from their healthy neighbors’ leftover leaves

The next time you’re about to enjoy a bite of chocolate, take a moment to thank the fungi and other microbiota that made it possible. Like the microbes humans start picking up at birth, organisms like Colletotrichum tropicale come to live on cocoa plants, helping them be more resilient to pathogens that would otherwise destroy the plant. Fortunately for farmers, and chocolate lovers, experiments suggest that this kind of fungal protection isn’t hard to spread between cocoa plants— sharing a bit of leaf litter from healthy neighbors should do the trick.

One of the biggest concerns for a cocoa, papaya and other tropical plants is Phytopthora palmivora, the “plant destroyer.” Once infected, a plant will start rotting at a variety of locations, from the roots to the fruit, and thus is a huge problem for farmers. The pathogen can be found in soil and water throughout tropical ecosystems, but fortunately protective fungi like C. tropicale aren’t too hard to come by either. Just as microbes can be shared between people when they touch, contact with leaf litter from healthy plants seems to be a good way to spread preferred microbes.

Testing leaf-based transmission

Researchers tested the effectiveness of leaf litter with cocoa plants initially grown from sterile seeds in sterilized chambers. Their leaves were verified as being fungus free before one-third of the plants had dead leaves from healthy cocoa plants placed in their pots. Other plants got mixed leaves from the forest, and some had none at all. They were all given a little time to grow outdoors in more “natural” conditions before purposely being exposed to P. palmivora. After three weeks, the plants with healthy cocoa leaves on their soil fared the best. DNA sequencing also confirmed that these plants leaves had a considerable population of the helpful fungus, C. tropicale.

While growing up in the leave litter of a healthy plant seems beneficial, there are limits to proximity. If a parent plant is infected, it can just as easily spread pathogens to its offspring. So cocoa farmers need to keep an eye on their plants to make sure the healthier plants are the ones dumping their leaves their neighbors.

Source: Litter Bugs May Protect Chocolate Supply, Scienmag