Cocoa Plants Find a Friend in Fungi

It's a sweet deal. Cacao trees—Nature's chocolate source—offer certain fungi a place to live and hang out. In return, the tiny tenants stand guard, ready to protect their plant-based homes from microbial attack.

That's the finding of scientists with the Agricultural Research Service (ARS) and their colleagues, who are looking for ways to protect Theobroma cacao, known as cacao, from destructive pathogens that can ruin the plant's cherished crop of cocoa beans.

In Latin America, where about one-third of the world's chocolate originates, the two most persistent cocoa spoilers are witches' broom and frosty pod rot. Right now, chemical fungicides are farmers' best defense against the diseases.

But experts at the ARS Systematic Botany and Mycology Laboratory in Beltsville, Md., and their collaborators have an all-natural alternative in mind. They've found that certain fungal endophytes, which take up residence in plants, make ideal roommates capable of keeping disease-causing microbes at bay.

Endophytes are fungi or bacteria that live within the nooks and crannies of living plants and trees but cause no apparent harm to their hosts. These live-in microorganisms set up shop pretty much wherever they want: in a tree's leaves, stems or trunk.

Gary Samuels, a mycologist at the ARS Beltsville laboratory, is part of a team of experts who are traveling the globe in search of new and promising endophytes. He named and described one recent discovery: Trichoderma ovalisporum. Samuels' colleagues, including Harry Evans with CABI Bioscience in the United Kingdom, found the fungus growing inside a tropical woody vine in Ecuador.

Laboratory and field studies show that this endophyte is effective at running off the frosty pod rot pathogen. If it continues to prove its worth, T. ovalisporum's spores could someday be applied to cacao tree flowers to help shield the plant—and its precious beans—from fungal attack.

Read more about the research in the June 2006 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.