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| Author: | N. van Berkel |
Abstract:
In glasshouse cultivation physiological disorders arise more readily than in the open.
The next three disorders, two of which are specific for glasshouse cultivation, will be given attention: tipburn in chinese cabbage, glassiness in lettuce/cucumber and leaf die-off in gerbera upon CO2 enrichment.
- In spring culture of chinese cabbage, tipburn often arises at the youngest leaves.
It is caused by Ca depletion in rapidly developing leaves.
It can be prevented by stimulating root pressure flow by covering the plants with plastic film during the nights.
- Glassiness in lettuce is a disorder mostly occurring from November till January.
The symptoms are watersoaked spots along the leaf edges and bounded by the veins.
If the spots prolong for much time the tissue may die and the lettuce becomes unsalable.
In the field, a low nitrogen level of the soil is conducive to the disorder.
It has been shown however that the electrical conductivity of the substrate is decissive and not the nitrogen concentration as such.
Further a negative correlation was found between nightly radiation and the presence of glassiness.
At low nutrient levels cucumber showed glassiness at the following circumstances: elevated CO2 level, covering with plastic film, leaf trimming.
Glassiness often coincides with guttation but the two phenoma may also occur separately.
Probably both phenomena arise from root pressure.
- In gerbera cv "Marleen" older leaves die off at elevated CO2 concentrations.
The higher the concentration is the more leaves die.
The first symptoms seen in leaves to die are tiny yellow spots.
Many spots together give rise to larger dead spots, finally
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