Fruitlet core rots black spot

FCR (Oxenham, 1962; Rohrbach and Apt, 1986) or black spot (Keetch, 1977) (also called fruitlet brown rot and eye rot (Snowdon, 1990)) is a descriptive term for a brown to black colour of the central part of an individual fruitlet (Fig. 9.26). FCR is caused by an infection by a pathogen or, more commonly, a group of pathogens. Botanically the central area of the fruitlet core is the septa (inverted Y) between the three seed cavities or locules (Fig. 9.27).

Fig. 9.26. Pineapple fruit slices showing fruitlet core rots caused by Penicillium funiculosum (left) and Fusarium subglutinans (right).
Fig. 9.27. Diagram of a cross-section of a pineapple fruitlet showing the internal parts.

Because individual or mixtures of pathogens may be associated with the FCR symptom, there is considerable confusion in the literature. The Penicillium and Fusarium fungi (Rohrbach and Apt, 1986), the round yeasts (M. Okimoto, unpublished results) and bacteria (D. Gowing, H. Spiegelberg, I. Yanagihara and J. Darroch, unpublished results) have been associated with the FCR symptom. In addition to the multiple pathogens, two mites have also been reported to be associated with the occurrence of FCR epidemics (Rohrbach and Apt, 1986; K.G. Rohrbach, unpublished results).

Two additional symptoms - IFC (Fig. 9.28) and LP (Fig. 9.29; Hepton and Anderson, 1968; Petty, 1977b) - are clearly associated with FCR caused by Penicillium infection (Rohrbach and Apt, 1986). The degree to which these symptoms develop appears to depend on the time of infection, the pathogen or mixture of pathogens present, the cultivar and environmental conditions. The IFC symptom can also be caused by boron deficiency in which case the symptoms are indistinguishable (K.G. Rohrbach, personal observation).

Two distinct levels of FCR occur in commercial production of 'Smooth Cayenne'

Fig. 9.28. Interfruitlet corking caused by Pénicillium funiculosum infections of the pineapple flower and subsequent reduction of growth of the individual fruitlet (could also be symptoms of boron deficiency).

(K.G. Rohrbach, personal observation): (i) a very low incidence of one to five fruitlets per 100+ fruits; (ii) a true epidemic, in which every fruit will have at least some FCR and many fruits will have multiple fruitlets infected (25 or more). It is theorized that the very low levels are the result of botanical malformations of individual fruitlets caused by disruptions in the normal phyllotaxis of the fruit (Kerns et al., 1936). Malformation of the fruitlet allows infection of the stylar canals and nectary ducts by a range of pathogens. In contrast, true epidemics result from the coincidence of optimum environmental conditions resulting in predisposed flowers, production of inoculum of the pathogen(s) and transport of the inoculum to potential infection sites.

Each major pineapple production area appears to have characteristic pathogens associated with the FCR symptom, probably

Fig. 9.29. Leathery-pocket symptoms caused by Pénicillium funiculosum in pineapple fruit cylinder.

as a result of the environmental conditions of the area (Rohrbach, 1980). For example, in Hawaii, Pénicillium and Fusarium species are most commonly associated with FCR (Rohrbach and Apt, 1986). In South Africa, Penicillium species are most commonly found (Keetch, 1977), while, in Brazil, Fusarium species are most commonly associated with the FCR symptom (Bolkan et al, 1979).

FCR and associated symptoms are of major economic significance only as epidemics, not at endemic levels. Fortunately, true epidemics are relatively sporadic in the 'Smooth Cayenne' cultivar and in the major commercial pineapple areas of the world. The disease could become more important if some of the more susceptible, low-acid 'Smooth Cayenne' cultivars and hybrid cultivars are grown commercially for fresh-fruit markets.

The FCR symptom is generally characterized by browning of the inverted 'Y' tissues

(septa) between the locules (Fig. 9.27). The degree of discoloration may vary from a very slight brown to dark brown or black. As mentioned previously, the FCR complex involves the fungi P. funiculosum and F. subglutinans, and the round yeast Candida guilliermondi. The pineapple tarsonemid mite, S. ananas, and the pineapple red mite, D. floridanus, are also associated with the FCR complex. While all of these organisms have been associated with the FCR symptom, little information has been published on the role of the yeasts as pathogens and the role of the pineapple red mite in Fusarium FCR. Considerable information is known and published on the Penicillium- and Fusarium-induced fruit diseases and the role of the pineapple tarsone-mid mite (Rohrbach and Pfeiffer, 1976b; Rohrbach and Taniguchi, 1984).

FCR symptoms produced by Penicillium species are dark to medium brown in colour, usually with a grey, water-soaked centre (Fig. 9.26). The colouring may extend into the non-carpellary tissue. Blue-green sporulation is frequently observed in the locules on the ovules (see Fig. 9.22). FCR symptoms caused by Fusarium species vary in colour from light through medium to dark brown and extend partially to completely down the fruitlet core (Fig. 9.26). FCR caused by Fusarium species is usually a 'dry7 type of rot, in contrast to the moister and softer Penicillium and yeast rots. Inoculations of fruit with Fusarium at different stages of development result in different symptoms. Very early infections result in light brown colour, while dark brown colour results from late infections (K.G. Rohrbach, unpublished results). White to pinkish mycelium frequently occurs in the seed cavities (indication of sporulation) (K.G. Rohrbach, personal observation).

FCR symptoms from yeast infections are usually light brown. The same yeasts causing FCR are associated with glassy spoilage (discussed below).

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