Black pod disease
| Black pod disease | |
|---|---|
| Common names | Black pod disease of cocoa |
| Causal agents |
Phytophthora palmivora Phytophthora megakarya |
| Hosts | cocoa (Theobroma cacao) |
| EPPO code | PHYTPL |
Black pod disease is caused by many different Phytophthora spp. pathogens all expressing the same symptoms in cocoa trees (Theobroma cacao). This pathogen if left untreated can destroy all yields; annually the pathogen can cause a yield loss of up to 1/3 and up to 10% of total trees can be lost completely. With the value of the cocoa industry throughout the world being so large there are much research and control efforts that go into these Phytophthora spp. pathogens.
This pathogen can be located anywhere on the cocoa trees but is most noted for the black mummified look it will give to the fruit of the cocoa tree. Staying ahead of the pathogen is the best means of control, the pathogen can be greatly reduced if leaf litter is not allowed to stay on the ground and if the pathogen gets out of hand chemical control can be used. This pathogen is mostly found in tropical areas where the cocoa trees are located and need rainfall in order to spread its spores.
The symptom of black pod disease is the necrotic lesion on cocoa pod with brown or black color, which eventually enlarged to cover the whole pod. White mycelia growth on lesions that appeared several days after infection is the sign for causal pathogen of black pod disease, which is Phytophthora spp.
Black pod disease starts when the infected pod shows some little yellow spots, which eventually turn brown and enlarge to a dark brown or black lesion within five days. The lesion is fast growing and covers the entire pod after eighth day of infection. The infection does not only occur on the pod surface, but also invades inside the pod affecting the beans. The growth of white mycelia on black pod is visible after 11 days and the sporulation is initiated. The dispersal of sporangia or zoospores through water, ants and other insects occurs at this stage and will infect other healthy pods nearby. Direct contact of a black pod with healthy pods also leads to the spread of disease. In addition, the infected flower cushion and mummified pods are the locations for P. palmivora survival during dry season, where the pathogen will grow and continue to infect other developing pods The infection occurs on any stage of pod development, where it causes wilting and dying of young pods and destroyed the beans of mature pods. The fully infected pods (the mummified pod), which then become dehydrated, are capable of providing the inoculum of P. palmivora for at least 3 years.P. megakarya causes the same symptom as P. palmivora, but the occurrence is faster and generally produces greater amount of spores. Both P. palmivora and P. megakarya also caused canker on bark, flower cushion and chupons, and cankers on the base could extend to the main roots. Cankers were identified as one of inoculum sources for black pod disease. Furthermore, the pattern of infection caused by P. megakarya starts from the ground and moves up to the canopy, however there is no distinct pattern of disease infection caused by P. palmivora was reported. This pattern of infection could be due to P. megakarya and P. palmivora that were found to survive in soil and P. megakarya could be surviving in the roots of a few species of shade trees found in cocoa plantation.
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Wikipedia