Crop-Specific Physiological Disorders - Fruit shape and splitting/cracking disorders

Greenhouse crops such as tomatoes, cucumbers, and capsicum may experience a number of issues with fruit shape and deformities. Misshapen fruit often results from issues during pollination and fruit set; however, some cultivars are more susceptible than others to these disorders.?Seedless cucumber types which set fruit without the need for pollination are the exception, as these may become deformed if unwanted pollination actually occurs resulting in seed development in the flesh. Tomato fruit can develop a condition termed ‘catface’ which describes deformity of fruits which typically occurs due to fruit set under cooler-than-optimal conditions.

In capsicum, fruit with uneven locule development and malformed fruit are also due to lower temperatures during flowering and fruit set. These problems are most common in unheated crops in temperate regions. Russeting or cracking and splitting of greenhouse-grown fruit such as tomatoes, melons and capsicum can have a number of causes. Fruit cracking is the splitting of the epidermis around the calyx and mainly occurs when there is a rapid net influx of solutes and water into the fruit (Olle and Williams, 2017). At the same time, genetic susceptibly, ripening or other factors reduce the strength and elasticity of the fruit skin (Leonardi et al., 2000).

?Cuticle cracking can occur at all stages of fruit growth; however, it is more common as fruits mature, particularly as colour develops (Olson, 2004). These physiological disorders are often linked to irrigation irregularities and are more prevalent during the later stages of fruit development or as fruit are starting to ripen. Irrigation of fruiting crops should be monitored and managed to prevent any drying within the root zone.

Crops which have suffered some?drying and then given a large irrigation volume will rapidly take up a large influx of water which can cause the fruit to swell and split. Rapid changes in nutrient solution EC can have a similar effect, with a sudden intake of water causing cracking and splitting of the fruit cuticle. Another cause of fruit splitting is heavy pruning of plants because sudden removal of large amounts of foliage may cause fruit to split as moisture is diverted into the fruit. High temperature and light levels are also associated with increased rates of fruit cracking (Peet, 1992).

In some tomato types such as the small cocktail varieties, fruit may split postharvest in response to rapid changes in temperature; this can be avoided by careful regulation of media moisture and EC levels in the later stages of fruit development. Harvesting cherry tomatoes in the morning has been found to give the highest rates of postharvest fruit cracking, while the lowest rates were found in fruit harvested in the evening (Lichter et al., 2002).?

Selection of cultivars of fruiting crops that have resistance to russeting and cracking can assist with prevention of these disorders. Crack-resistant cultivars of tomato are generally associated with a thicker cuticle (Sadhankumar et al., 2001) and an epidermis that stretches well during fruit expansion.

Reference: Hydroponics and Protected Cultivation A Practical Guide?by Lynette Morgan.