Translated from the web site www.shaham.moag.gov.il Hebrew version article by Omar Zeidan

Calcium is considered a macro element which is up taken in high quantities by the plants.

A high percentage of Calcium is present in cell walls and membranes of plants. Under stress conditions, Calcium is not evenly distributed within the developing fruits. As a result of a Calcium deficiency, the fruit tissue at the blossom-end of the fruit collapses finally becoming dark brown in color. This phenomenon is known as Blossom-End Rot. The phenomenon is common to developing fruits when they have reached 30-70% of their final size. It was observed in an experiment in flowing nutrient solution that, when the electrical conductivity of the solution (EC) is higher than 3 dS/m-1 and Calcium concentration is lower than 100 ppm, the incidence of Blossom-End Rot increases. The movement of Calcium within the plant is usually by the water movement in the Xylem in the transpiration process. However, the source of most of the water reaching the tomato fruit is the Phloem and therefore the quantity of Calcium reaching the fruits is relatively small compared to the quantity of Calcium reaching the leaves. The result is that even short stress events or a combination of several factors can increase the phenomenon of the Blossom-End Rot. Since cells and membranes are created in the growing zones of the plants, they can be the first plant parts in which lack of Calcium is expressed.

Calcium is an ion that moves with difficulty within the plant and is not transferred from older plant tissue to younger tissue. Therefore a lack of Calcium is invariably noted in the young plant tissue and especially in growing fruits. In cases of extreme deficiency, damage is caused to the young plant tissue resulting in browning of young leaf edges or yellowing of the tissue between the veins of the young leaves.

For tomato fruit dry matter, Calcium concentrations in fruit damaged by Blossom-End Rot were less than 0.08% while Calcium concentrations in tissues from healthy fruits were between 0.12-0.25%. Calcium concentrations in leaves with Calcium deficiency symptoms were less than 0.2% while concentration levels in healthy leaves were between 2-4 %.

The following is a list of the main factors causing
an increase in the phenomenon of Blossom-End Rot in fruits:

• Lack of Calcium in soil solution or soil media.
• Sudden (temporary) water stress.
• Salinity stress as a result of salt accumulation in the root zone.
• Competition of several (mostly positive) ion elements in the soil.
• Low relative humidity and severe hot dry spells.
• High temperatures accompanied by high humidity conditions.
• Limited and undeveloped root zone.
• Sensitive varieties - varieties with elongated fruit are normally more sensitive to Blossom-End Rot.

Means to reduce the phenomenon

• Sufficient Calcium supply in the irrigation water.
• Regularly-timed irrigations and avoiding even short-term water stress.
• Avoiding the accumulation of excessive fertilizer in the soil or growing media. Under these circumstances, irrigation quantities should be increased to allow leaching of excessive salts.
• Using potassium and magnesium fertilizers as per plant requirements. Using higher concentrations of these elements in the soil inhibits Calcium uptake by the plants.
• Maintaining a high relative humidity in the greenhouse (70%) especially in the Autumn and Spring.
• Building up a deep and wide root zone system and a strong plant to enable the plant to withstand stress situations.
• Growing varieties tolerant to Blossom-End Rot.