Calcium dynamics of reproductive apple buds during the dormant season in the Western Cape, South Africa
2019
Lötze, Elmi | Frazenburg, Madelaine | Turketti, Sandy S. | Dreyer, Leanne
Calcium (Ca) deficiency in apples results in unwanted physical disorders in mature fruit that reduce fruit value. Ca deficiency associated with bitter pit is already prevalent early in the season, as it is initiated a few weeks after full bloom. Information regarding Ca concentration in reproductive buds or bud tissues is lacking, thus we investigated the Ca concentration in reproductive buds of the bitter pit susceptible ‘Braeburn’ and non-susceptible ‘Cripps Pink’ apple cultivars during the dormant season. Wavelength-dispersive x-ray spectroscopy (WD SEM) was used to quantify total Ca concentration of parenchyma and vascular tissues, from June to September, for two seasons (2012 and 2014). Results showed a changing trend in Ca concentration from June to September for total Ca concentration and between cultivars. Total Ca concentration was the highest in ‘Cripps Pink’ during the whole period and related to the non-susceptibly to Ca related disorders. Ca concentration in ‘Cripps Pink’ declined towards September in contrast with the increasing trend of ‘Braeburn’. This may indicate that the total Ca concentration of the buds, and not the change of Ca concentration in buds during winter, is associated with a higher Ca status of fruit on non-susceptible cultivars. The actual Ca concentration of ‘Cripps Pink’ at the end of August was still higher than that of ‘Braeburn’. Results may be explained partly by the time of primary xylem formation in the bud, which happens earlier in ‘Cripps Pink’, as well as the associated increase in Ca translocation, indicating the role of generic differences between cultivars, contributing towards final changes in the inherent Ca concentration at the beginning of the dormant season.
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