A. Blanco

Inhibition of vegetative growth in red apple cultivars using prohexadione-calcium

Summary Prohexadione-Ca (ProCa) has been evaluated as a growth inhibitor in the vigorous red apple cultivars ‘Fuji’ and ‘Royal Gala’. Greatest inhibition of shoot growth was obtained when ProCa was first sprayed at about 200 mg l–1 from full bloom (FB) up to 12 d after full bloom (DAFB). Shoot regrowth often occured later in the growing season, and a second application of ProCa was then needed to maintain growth inhibition. Inhibition of shoot growth was due mainly to a reduction in internode length. No effects on yield have been found, except for cv. ‘Royal Gala’, where an increase in crop-load and a decrease in fruit size were recorded. Fruit quality parameters were not affected; but, in cv. ‘Fuji’, the red colouration of fruit was promoted by ProCa, particularly when repeated sprays of the chemical (at 125 or 250 mg l–1) were made. Changes in hue, chroma and lightness were recorded on both the blushed and shaded sides of fruit. No effects on fruit colour were seen in ProCa-treated cv. ‘Royal Gala’ trees.

Differential effects of prohexadione-calcium on red colour development in 'Royal Gala' and 'Fuji' apples

Summary Two different spray programmes for split application of prohexadione-calcium (ProCa) were tested on ‘Royal Gala’ and ‘Fuji’ apple trees (Malus domestica Borkh.) to evaluate their effect on red colour development in the fruit. Applications of ProCa split into two sprays at full-bloom and 60 d after full-bloom (DAFB) were sufficient to control shoot growth in these cultivars. A third application (95 DAFB) did not result in any additional beneficial effects. In addition to obtaining significant reductions in shoot elongation, reductions in leaf area were also noted. No effects on yield or on various fruit quality parameters resulted from the ProCa treatments, with one important exception, fruits from ‘Fuji’, a late-season cultivar, displayed a greater percentage of fruit surface with red colour. Simultaneously, a deeper red colour was recorded on the blushed side of the fruit, resulting from greater concentrations of anthocyanins and carotenoids. In contrast, fruits of ‘Royal Gala’, a mid-season cultivar, did not show differences in fruit colouration following treatment with ProCa.

Visual Detection of Calcium by GBHA Staining in Bitter Pit-affected Apples

Bitter pit is a physiological disorder of apple fruits apparently caused by a localized calcium deficiency or imbalance in fruits associated with low levels of calcium in the flesh. A new, highly selective method using glyoxal bis(2-hydroxyanil, GBHA) was tested to reveal the presence of calcium within the fruit as a red stain. Water-soluble and insoluble calcium was analyzed by capillary electrophoresis and atomic absorption spectroscopy in pitted regions, adjacent sound areas and pulp from sound apples. Both methods, selective calcium staining and mineral analysis, showed that calcium accumulates in the pitted areas of apples affected by bitter pit. However, in mechanically inflicted wounds, the pulp of the apple was heavily stained but not the corresponding fingerprint, indicating a similar mechanism of insoluble calcium accumulation but a different distribution of soluble calcium compared to the pits.

Prohexadione-calcium effects on the quality of ‘Royal Gala’ apple fruits

Summary To study the effects of prohexadione-calcium (Pro-Ca) on fruit quality, an experiment was performed in 2002 in which trees were treated with two different concentrations of Pro-Ca and left with different crop-loads. Increasing levels of thinning resulted in smaller yields, but greater fruit sizes, which followed a curvilinear pattern when plotted against crop-load. The soluble solids content and titratable acidity of fruits decreased linearly with increasing crop-load. Fruit skin chromaticity values also changed. Luminescence increased, while a* values decreased linearly with increasing crop-load, indicating more reddish and darker coloured fruits on trees subjected to very heavy thinning. In addition, the concentrations of soluble sugars in fruits changed with the level of cropping; fructose and glucose concentrations increased with crop-load, while sorbitol and sucrose decreased. The application of Pro-Ca shortly after full-bloom inhibited shoot elongation growth, but did not result in changes in yield or in any of the fruit quality parameters analysed.

Polypeptide pattern of apple tissues affected by calcium-related physiopathologies

Polypeptides from the apple pulp of Smoothee Golden Delicious and White Renete apples were resolved by 1-D denaturing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). According to the electropherograms, there were lower concentrations of 88, 74, 70.6 and 47.5-42kDa proteins in bitter pit spots. Proteins weighing 30 and 26kDa were rare in sound pulp but frequently appeared in pits and adjacent tissue. Finally, a novel 18kDa protein was found in bitter pit spots in both varieties, and also in chemically induced corky lesions either by magnesium infiltration or ammonium oxalate cortical injections. The available data suggested that the novel protein might be an inhibitor of pectinmethylesterase, a small heat stress protein (smHSP) or a product of the Ypr-10 gene family identified with ‘Mal d 1’, the main allergen of apples. To elucidate the possible smHSP nature of the 18kDa, a set of apples were heated at 40°C for 20h, developing this protein in both the oxidised tissue and in the adjacent.

Effects of paclobutrazol application and fruit load on microelement concentrations in peach leaves

‘Catherina’ peach trees (Prunus persica (L.) Bastch.) were soil-treated at full-bloom with paclobutrazol (Pbz) or left untreated and one month later fruit-thinned to leave four different cropping levels from full crop to none. Leaf samples were harvested on different dates from July 9 to 31 October and analysis of mineral elements made by AAS. The concentrations of Fe and Mn were always greater in leaves from Pbz treated trees than in the controls, while Zn and Cu concentrations remained unaffected. On all sampling dates, the concentration of Mn decreased linearly with increasing levels of cropping. No effects of the cropping level were observed in the concentrations of the other elements analysed.

Physiological effects of prohexadione-calcium in apple trees: effects on parameters related to photoproductivity

Summary Different prohexadione-Ca (RegalisTM, Pro-Ca) treatments were applied as foliar sprays to ‘Royal Gala’ and ‘Smoothee Golden Delicious’ apple trees to asses its effects on different physiological traits, under the growing condition of the Middle Ebro Valley (Spain). The application of Pro-Ca resulted in a decrease in leaf area, as well as fresh and dry leaf weights, and an increase in specific leaf weight. Greater light penetration through the canopy was recorded, indicative of a lower canopy density, resulting both from the inhibition of shoot growth and leaf extension growth. In addition, increases in leaf chlorophyll concentrations, and photosynthetic rates were found, which could account for the lack of effect of Pro-Ca on overall tree growth.