Fusariosis

Fusariosis is caused by the fungus F. subgluti-nans which is the conidial stage of G. fujikuroi Edwards. Whether or not F. subglutinans in

Brazil is the same as the Fusarium species causing FCR is not definitive in the literature. Laville (1980) considers F. subglutinans a distinctly different species from the Fusarium causing FCR. Other authors have attributed FCR to F. moniliforme (Oxenham, 1962; Guerout, 1974; Rohrbach, 1983). The disease, first described in Argentina in 1954, was first reported in Brazil in 1964 and within 10 years had spread over the entire country (Laville, 1980; Rohrbach, 1983).

The fruit symptoms at low severity levels are similar to those of FCR, which vary from light through medium to dark brown, extending partially to completely down the fruitlet core. FCR from Fusarium sp. is usually a 'dry' type of rot (see Fig. 9.26). In Brazil, the symptom is not limited to a single infected fruitlet, as in typical FCR reported in other pineapple production areas. Fruit symptoms involve multiple fruitlets, with the infected area of the fruit surface appearing off-colour initially and later becoming sunken, with profuse pink sporulation and exudation of gum (Fig. 9.30). Gum exudation can be confused with the exudation from Thecla wounds (see Fig. 9.24; Laville, 1980).

In Brazil, the disease causes major losses in the three major cultivars, 'Perola', 'Jupi' and 'Smooth Cayenne' (Rohrbach, 1983). Levels of fruit infection can vary from 5 to 75% (Laville, 1980). Infection is thought to occur through open flowers, although major levels of disease also occur from inoculations to the developing inflorescence (Ventura et al., 1981). Infection of the inflorescence and fruit also occurs from injuries caused by insects, particularly the bud moth, T. basilides. Once the developing fruit is infected, secondary infections can occur on the developing slips or suckers. The infected seed material is then distributed to new planting areas, thus infesting new sites. Soils can remain infested for several months. Spread within infested fields is primarily by insects but may also be by wind (Laville, 1980). Free conidia of F. subglutinans can survive for 6-13 weeks in soil, depending on moisture and temperature, with survival being highest in dry soils. Survival in pineapple tissue in soil is less than 10 months (Maffia, 1980). Optimum tempera-

Fusariosis
Fig. 9.30. Pineapple fruit in Brazil showing fusariosis caused by Fusarium subglutinans.

tures for growth are 25°C, with a range of 5°C to 35°C (Camargo and Camargo, 1974).

Control of fusariosis is most effective by planting disease-free seed material and by controlling insects, particularly the bud moth (Laville, 1980). Fungicides, such as captafol at 700 g a.i. ha-1, starting at differentiation through harvest at 20-day intervals, have given good control of the fruit-rot phase in Brazil (Bolkan et al, 1978).

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