Department of Biology

Leaves host a diverse fungal microbiota, but it remains unknown how these communities assemble and affect plant health.

Natalie Christian, a Ph.D. candidate in the Clay lab, and colleagues manipulated local environmental factors and showed that leaf litter exposure and vertical stratification have dramatic effects on cacao’s microbiome. Remarkably, exposure to litter from cacao adults significantly reduced pathogen damage on conspecific seedlings—an effect attributable to microbiota transferred from litter that enriched the seedling microbiome with fungal species that enhanced pathogen resistance. Analogous ideas of “seeding” a healthy microbiome into hosts have been documented in human microbiome studies, including fecal transplants and maternal transmission of a healthy microbiome to infants.

Study results provide hope for cacao farmers. Phytophthora palmivora, a fungal pathogen, infects cacao tissue and is responsible for 10 to 20 percent of cacao crop loss worldwide. 

Endophytes are organisms, often fungi and bacteria, that live between living plant cells. Their relationship with the plant varies from symbiotic to pathogenic. The beneficial endophyte Colletotrichum tropicale has an inhibitory effect on P. palmivora.

Christian and colleagues found that C. tropicale is passed in great abundance from the healthy cacao leaf litter to the seedlings. On cacao farms where leaf litter and plant debris are removed from the field, boosting the health of seedlings may be as easy as returning the leaf litter to transfer beneficial microbiota to the young plants.