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diseases of impoRtant cRops in chiapas

Cacao (Theobroma cacao)

Black pod (edited information from Guest, 2007). Black pod, the most damaging and wides-

pread disease of cacao, is caused by 10 different species of Phytophthora; P. palmivora (pantro-
pical), P. megakarya (West Africa), and P. capsici (tropical America) are the most important. Pod

lesions begin as small, hard dark spots on any part of the pod, at any stage of its development.

Lesions spread rapidly to the entire pod surface and internal tissues, including the beans, of

susceptible genotypes within a few days. Affected pods become mummified, which in the case

of P. palmivora provides a reservoir of inoculum for at least 3 years (Dennis and Konam, 1994).

Under humid conditions a single pod can produce up to 4 million sporangia that are dissemi-

nated by rain, ants, flying insects, rodents and bats, on contaminated harvesting and pruning
implements, and in contaminated soil.

P. palmivora infects bark, flower cushions and chupons causing cankers. Cankers at the

base of the trunk may extend to the main roots. Cankers are often hidden by the bark but

often exude a reddish gum or infect flower cushions, killing the flowers. Girdling cankers cause

sudden death of up to 10% of trees each year, reducing production and imposing an extra cost

in replanting and lost production as replanted trees mature. In humid conditions, P. palmivora

also causes seedling and leaf blight. While infections of fine roots are also common, these ap-

pear to be more important as a source of inoculum than as a cause of serious injury to the tree.

Although symptoms appear year-round, the most severe epidemics coincide with the
proliferation of sporangia and insect vectors during the wet season. Zoospores can encyst, ger-

minate and penetrate host tissues within 20-30 min in free water. Under favorable conditions

lesions produce sporangia within 48 hours of infection.

These soilborne pathogens move to aerial parts of the cacao plant via rainsplash, aerosols

and contaminated equipment. Vectors, including tent-building ants and flying beetles, move

Universidad Autónoma de Chiapas