Page 187 - FRUTAS DEL TRÓPICO

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diseases of impoRtant cRops in chiapas

brown. A second type of symptom, chocolate spots, appear as slightly depressed, reddish-
brown, irregular to circular, sharply defined spots 1 to 10 mm in dia. They enlarge rapidly as

fruit ripens to form characteristic, sunken lesions.

The primary inoculum, conidia, occurs on senescing petioles and leaves and is dissemi-

nated by wind or rain. The fungus infects intact, unwounded, immature green fruit in the field.

Spores germinate, form appressoria on the fruit surface, and penetrate the cuticle directly with

the aid of enzymes and mechanical pressure (Latunde-Dada, 2001; Ploetz et al., 1994; Ploetz,

2003). The sub-cuticular hyphae remain latent until fruit ripening commences. High tempera-

tures and relative humidity favor disease development.

Anthracnose is managed by applying fungicides to fruit in the plantation, particularly
when weather conditions favor disease development. Post-harvest fungicide and hot water

treatments also provide control.

Papaya bunchy top. Papaya bunchy top, caused by Rickettsia sp., is a serious disease that

often limits commercial production in the American tropics (Ploetz et al., 1994; Ploetz, 2003).

The initial symptoms include diffuse chlorosis in young leaves with a reduction in the growth of

leaves and petioles. Small discrete water-soaked spots develop on affected petioles and stems,

later developing into irregular blotches about 1 to 2 mm in dia. Petioles are rigid, almost ho-
rizontal and shortened. Leaf blades are thickened, stiff, cupped downwards with marginal and

interveinal chlorosis and necrosis. Apical growth ceases, which, with the shortened interno-

des, gives plants a bunched appearance (Cook, 1972). Chronically affected plants often have

only a tuft of small leaves at the apex. Flowering and fruit set seldom occurs in affected plants

(Ploetz et al., 1994; Ploetz, 2003). The absence of latex flow from fresh puncture wounds in

leaves, stems and fruit is a valid test for the disease.

Universidad Autónoma de Chiapas