Researchers at Stellenbosch University studied the calcium content in dormant reproductive apple buds of four apple cultivars. The 'Royal Gala', 'Cripps Pink', 'Golden Delicious' and 'Braeburn' apple cultivars were quantified over two seasons.

The calcium concentrations were quantified with a wavelength-dispersive X-ray spectrometry detector (WDS). This is a non-destructive technique to measure elemental information in different materials. Results showed a variation in calcium concentrations in the different tissue areas of the different cultivars.

Results indicated that there was a higher xylem calcium concentration in June of the 'Cripps Pink' and 'Royal Gala' followed by an increase towards September. At the same time there was a reduction in spur calcium concentration which indicates that reserve calcium from the spur is allocated towards the xylem.

Trends in the 'Golden Delicious' and 'Braeburn' apple cultivars were not as clear and did not always follow the same pattern. Later formation of primary xylem in the dormant bud of these cultivars explains the lower calcium concentrations and difference in calcium distribution in these two cultivars compared to 'Cripps Pink' and 'Royal Gala'. The latter two are less susceptible to calcium-related deficiencies like bitter pit.

• The article 'Dynamics of nutrient allocation from reserve tissues, using calcium as a model in dormant, reproductive apple buds of four apple cultivars' was published in Acta Holticulturae (2022) and is available online​.​

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For more information, contact:

Madelaine Frazenburg

E-mail: mrfsem@sun.ac.za

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