Miscellaneous physiological fruit diseases

Woody fruit

Woody fruit is a disease of unknown cause. The disease is characterized by brown streaks distributed throughout the fruit tissue, which is very woody and hard in consistency. The disease is associated with certain clones of 'Smooth Cayenne' and therefore is assumed to be of genetic origin. Roguing at harvest is used to eliminate seed material from plants showing symptoms.

Sun scald and frost injury

Sun scald is characterized by a discoloration of the fruit shell, which ranges from yellow to tan or black on the side of the fruit exposed to the sun. The internal tissues are usually a pale grey colour, but, when severe, the affected area becomes sunken and desiccated. Fruits that fall into an exposed or reclining position are much more susceptible. On clear, calm days, temperatures of 50-54.4°C have been recorded in exposed fruit (K.G. Rohrbach, unpublished results). Where sun scald is a problem in summer months (e.g. Australia, South Africa, Taiwan and Brazil) straw, weeds or shredded paper may be used to cover the exposed side of the fruit for control (Lim, 1985). Sprays of a 4:1 mixture of talc and bentonite are used by larger growers in Australia to reduce incidence of injury.

Frost injury occurs occasionally in some areas in Australia. Symptoms are shell discoloration and cracking between the eyes.

Fasciation/multiple crowns

Multiple crowns (two or more) develop when young fruit are exposed to high temperatures early in the development stage. Because nothing is known about the stage of fruit development most susceptible to high temperatures, no controls are available. The problem is mainly important where fruit are to be sold fresh with the crowns attached. In Australia, multiple crowns are trimmed to one to improve appearance and to facilitate packing in boxes.

Fasciation is an abnormal development of the inflorescence and crown, resulting in a flattening of the upper part of the fruit with multiple crowns ranging from two to many. Fasciation has been associated with genetic and environmental conditions, although Py (1952) has indicated that the phenomenon is not hereditary. Cultivars such as the 'Smooth Cayenne' are less susceptible than the 'Singapore Spanish'. Within the 'Smooth Cayenne' cultivar, certain clones are much more susceptible than others.

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