Browsing by Author "Frazenburg, Madelaine"

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    Anatomical survey of the formation of primary xylem and nutrients supply to the reproductive apple bud
    (Stellenbosch : Stellebosch University, 2017-03) Frazenburg, Madelaine; Dreyer, L. L.; Lotze, Elmi; Turketti, S. S.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Apple (Malus domestica Borkh.) is a deciduous fruit species, which is subject to dormancy before bud break occurs in spring. Although not noticed externally, anatomical changes occur in the reproductive bud during this dormant period, including formation of the carpels, enlargement of the petals and carpel and anther elongation. In this study, we determined i) the time of primary xylem formation as influenced by cultivar, month and/or climate (expressed by winter chilling) and ii) the distribution and quantification of a selected nutrient calcium (Ca) in, (a) the primary xylem tissue as well as (b) in reserve tissues (spur, leaf and apical meristem). Four different commercial apple cultivars were selected for this investigation. Golden Delicious and Braeburn represented cultivars with typical Ca deficiency symptoms in the fruit if additional Ca is not applied, whereas Royal Gala and Cripps Pink represented cultivars in which Ca related problems occur less frequently. Golden Delicious and Royal Gala are cultivars associated with high chilling requirements, and Braeburn and Cripps Pink, with medium chilling requirements. Sampling of dormant buds occurred during June, July, August and September in 2012, 2014 and 2015. The different cultivars used for this investigation were cultivated in Stellenbosch and Elgin. Although these regions are both in the Western Cape Province, the Elgin region is an area with a higher chill unit accumulation than Stellenbosch. Light, fluorescence and scanning electron microscopy imaging techniques were used to study the anatomy of primary xylem development. To differentiate the degree of lignification in primary xylem from secondary xylem, samples were imaged with a Zeiss LSM880 confocal microscope equipped with ZEN 2 software. Scanning electron microscopy images were acquired using a Zeiss Merlin FEG Scanning Electron Microscope (SEM). After the time (month) of primary xylem establishment in the bud was identified, Ca concentration (%) was quantified in reproductive apple bud tissues of all four cultivars during three seasons (2012, 2014 and 2015). Ca concentration was quantified with Wavelength Dispersive Spectrometer (Oxford Instrument® Wave Dispersive X-ray Spectrometer). Ca was simultaneously quantified with Electron Dispersive X-ray (Oxford Instrument ® Energy Dispersive X-ray). In Golden Delicious and Braeburn, the process of secondary xylem development commenced earlier than in Cripps Pink and Royal Gala. While this process is slow in Cripps Pink, xylem development proceeds much faster in Royal Gala and changes from having only primary xylem in July to having secondary xylem a month later. The timing and duration of xylem development in Cripps Pink and Royal Gala were similar in the Stellenbosch and Elgin regions in June, but differed in July and August in all three seasons. Results clearly show differences in Ca distribution and Ca concentration in the tissues of dormant reproductive apple buds of the four cultivars studied. High Ca levels were noted in the spur transport tissue of Royal Gala, Cripps Pink and Braeburn during June, with considerably lower levels of Ca in the same region in Golden Delicious. Cripps Pink and Royal Gala have a higher Ca concentration in the xylem in June, followed by an increase in Ca concentration towards September. The reduction in Ca concentration in the spur during the same period may indicate that reserve Ca from the spur is allocated towards the xylem. This needs further investigation. Although trends were not as clear in Golden Delicious and Braeburn and did not always follow the same pattern, observations in these cultivars differed from those in Cripps Pink and Royal Gala, confirming the higher presence of primary xylem reported previously. Thus, later formation or presence of primary xylem in the dormant bud of these cultivars may partly explain the lower Ca concentrations and difference in Ca distribution between tissues compared to Cripps Pink and Braeburn.