Page 190 - FRUTAS DEL TRÓPICO

190 Frutas del trópico

1994; Ploetz, 2003). A causal role for PMWaV-2 was reported recently. Plants that were in-
fected with PMWaV-2 and infested with mealybugs developed symptoms of the disease, but

no symptoms developed on plants that were only infected or infested. Although PMWaV-1

and the badnavirus were often detected in symptomatic plants in the field, they did not cause

mealybug wilt symptoms alone or in combination with mealybug feeding. The pink mealybug,

Dysmicoccus brevipes, and the grey mealybug, D. neobrevipes, vector PMWaV-2. When ants

are controlled and mealybug predators and parasites are present, mealybug wilt is usually not

a problem.

Phytophthora heart rot and root rot. Worldwide losses are highly variable. Those caused

by heart rot result from plant mortality, whereas those from root rot are from reduced fruit
size and quality or suppression of plant growth and yield; in cooler environments with high

rainfalls, root rot can eliminate ratoon crops.

Phytophthora cinnamomi, is the primary heart rot pathogen, especially at moderate tem-

peratures (19-25°C); P. nicotianae and P. palmivora are apparently more important above 25°C.

Young leaves of affected plants fail to elongate and become chlorotic. The terminal whorl of

leaves leans to one side of the plant and is easily removed.

P. cinnamomi, P. nicotianae and Pythium arrhenomanes are root rot agents (Erwin and Ribie-
ro, 1996). They cause leaf growth to slow or stop, leaves to redden, and leaf tips and margins

to yellow and eventually become necrotic. Symptoms develop slowly. If conditions become

dry following infection, affected plants may appear reddish as if under severe drought stress.

As with severe mealybug wilt, root damage can be extensive, and affected plants can easily be

pulled from the soil.

A combination of strategies is used to manage these diseases. Most important is the im-

provement of soil drainage with increased surface flow and planting on raised beds. Preplant

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