Ceratocystis Wilt of Cacao  

Mal de machete or Ceratocystis wilt of cacao, caused by a host-specialized form of Ceratocystis fimbriata, now known as C. cacaofunesta, can be a serious disease of Theobroma cacao in Latin America, where the fungus is believed native.

The disease was not recognized in the southern part of the state of Bahia, Brazil until 1998 and is starting to cause significant losses to a crop already seriously compromised by witches' broom.

Asha Ram of CEPLAC in Itabuna, Brazil, opens a ripe cacao pod with stacks of seeds covered with a delicious, white pulp.

Infected trees show limp, brown foliage on a single branch or across the whole tree, depending if only a branch or the main stem is infected.

 The fungus moves through the xylem, often concentrating in the vascular rays, causing a deep stain wherever it grows. It moves systemically through the plant like a vascular wilt fungus, but it more readily kills the parenchyma tissue than would a classic wilt fungus.

The fungus will also kill the cambium and bark tissue, creating a canker on the stem or branch. 

  

 

 

 

 

 

 

 

Ambrosia beetles of the genus Xyleborus are attracted to the diseased trees and bore into the branches or main stem, as seen in the two top photos. The frass from ambrosia beetles is pushed to the outside of the stem or branch, seen on the base of the tree above as light, powdery masses. This frass contains viable inoculum of the fungus and may be spread by wind or rainsplash.

Alternatively, the fungus will sporulate heavily on the cut surfaces of diseased branches, shown here as black to gray patches on the end of a diseased cacao branch in Trinidad. These sporulating mats produce perithecia (fruit bodies) that exude sticky spore masses for insect dispersal. The mats produce a banana-like odor that attracts fungal-feeding insects, which can serve as vectors.

Spores in the wind-dispersed frass or spores carried by fungal-feeding insects can infect fresh wounds. The name 'mal de machete' comes from the association of such infections with machete wounds.

 

Many of the diseased trees in South Bahia show heavy infection at the base, perhaps due to infection of wounds near groundline or through the roots.

Although not investigated in cacao, Ceratocystis fimbriata in other hosts can infect through the roots. Like these other forms of C. fimbriata, the cacao pathogen forms dark, thick-walled spores that can survive in the soil, thus providing a third inoculum source.

Possible Control Strategies

Resistance to Ceratocystis wilt has been identified in cacao. Where the disease is common, such resistance should be used along with resistance to witches' broom, black pod, or other diseases.

Sanitation should also be practiced, disposing of infected branches and stems before Xyleborus beetle attack and before the fungus has a chance to sporulate on the cut ends of branches and stumps.

Wound treatments with tree paints or fungicide pastes on uninfected trees should also help control the disease.

Thanks to my Brazilian cooperator, Dr. Acelino Alfenas from the University of Viscosa, and our colleagues at CEPLAC, Drs. Asha Ram, Luiz Bezerra, Stella Dalva V. Midlej Silva, and Milton. Also thanks to Dr. Luadir Gasparoto, Eduardo Morales (EMBRAPA) and Rogerio Hanada (INPA) in Manaus, who helped us search for Ceratocystis on cacao in the Amazon (thankfully, we found none). Dr. Jean-Marc Thevenin and Lambert Motilal of the Cacao Research Institute (University of the West Indies) were a great help in showing me the disease in Trinidad. Special thanks to the National Science Foundation for supporting our work on Ceratocystis.

 

For more research on Ceratocystis: CERRES.html

To get back to Diseases Caused by Ceratocystis: CeratoDis.html  

For more pests of cacao: http://www.oardc.ohio-state.edu/cocoa/

For further cacao information: menuicco.htm

To get back to Tom Harrington's homepage: homepage.html

 Lasted updated January 2, 2000