There is a strong variety-effect on the occurrence of dark spots just underneath or in the fruit skin of yellow courgettes. High-yielding varieties are relatively susceptible to the phenomenon. This was found in a study carried out by Wageningen UR Greenhouse Horticulture, financed by the Product Board for Horticulture.
Brown spots are frequently occurring in the fruit skin of yellow courgettes. Symptoms are often still absent at harvest but many spots may show up in the yellow fruits within a few days in the trade channels. This is of course unwanted. Other causes, besides variety, have been investigated.
Variety effect
Variety effects were always clearly present in the various storage tests. This means that the grower can strongly influence the extent of the occurrence of spots by variety selection. But other factors are also playing a role in variety selection, such vigour, production, fruit shape and colour.
The differences were small in early crops of the same variety; correlations with cultivation conditions were therefore difficult to establish. Later in the season (mid June), however, clear differences showed up between yellow courgette crops in foil tunnels or greenhouses, when the brown spots were more superficial. Careful harvesting, grading and packing was found to have an effect.
Storage conditions
A low storage temperature did not result in more spots but storage at 10 oC and lower did result in low-temperature decay in the form of strongly sunken spots between the ribs near the neck and a bumpy skin. Effect of storage together with ripening fruit (ethylene) or different air humidity levels could not be demonstrated. A relationship between the concentrations of major and minor trace elements in the fruits and the occurrence of spots has neither been found. A thicker fruit skin seemed favourable in view of the occurrence of the spots. After longer storage these fruits also suffered less from dried necks and bulges on the skin.
The brown skin is probably caused by oxidation of polyphenols in the fruits. A high anti-oxidant concentration, such as ascorbic acid, i.e. vitamin C, could suppress this process.