Page 180 - FRUTAS DEL TRÓPICO

180 Frutas del trópico

to the cavendish cultivars in the 1960s. It is widely spread and now found in most banana-
producing regions.

The first internal symptom, a reddish brown discoloration of the xylem, develops in fe-

eder roots, the initial sites of infection. It progresses to the rhizome and is most prominent

where the stele joins the cortex. As the pseudostem is colonized, faint brown streaks or flecks

become evident on and within older leaf sheaths. Eventually, large portions of the xylem turn

brick red to brown. The first external symptoms are a yellowing of the oldest leaves or a lon-

gitudinal splitting of the lower portion of the outer leaf sheaths on plants that are usually more

than 4 months old. This is followed by wilting and buckling of leaves at the petiole base. In

some cases, these leaves remain green. As the disease progresses, younger and younger lea-
ves collapse until the entire canopy consists of dead or dying leaves.

Four races of F. oxysporum f. sp. cubense have been described, only three of which affect

banana (race 3 is a pathogen of Heliconia spp.). Race 1 caused the epidemics on ‘Gros Michel’

and also affects ‘Maqueño,’ ‘Silk’ (‘Manzano’), ‘Pome,’ ‘Pisang Awak,’ and the hybrid ‘I.C.2.’

Race 2 affects cooking bananas, such as ‘Bluggoe,’ and some bred tetraploids. Race 4 is most

destructive since it affects race 1 and race 2 suscepts as well as the cavendish cultivars, plantains

and other bananas that are resistant to races 1 and 2.
The pathogen spreads in soil and running water, and on farm implements and machinery.

However, infected rhizomes (“suckers”) that are used as seedpieces are responsible for the

widest and most effective dissemination. Susceptible clones usually can not be replanted in

infested sites for up to 30 years due to the long-term survival of the pathogen (Stover, 1962;

Waite and Dunlap, 1953). The disease is managed in infested soils with resistant cultivars (see

Table 7). Where the disease has not been found, clean planting materials (preferably tissue-

culture plantlets) can be used. Effective biological and chemical measures are not available.

Universidad Autónoma de Chiapas