Prohexadione–Ca inhibits vegetative growth of ‘Smoothee Golden Delicious’ apple trees

Experiments to test the effectiveness of prohexadione–Ca as a growth inhibitor in apple trees have been carried out for 3 years in the Middle Ebro Valley (Spain). Also, effects on fruit quality and flower initiation were evaluated. The application of 100–400 mg l⁻¹ of prohexadione–Ca between 12 and 30 days after full bloom (DAFB) to ‘Smoothee Golden Delicious’/M9 apple trees resulted in the inhibition of shoot growth, the effect increasing with concentration, and a greater inhibition was obtained when the trees were first sprayed 12–20 DAFB. A second spray was usually needed to avoid a regrowth of the shoots. The effectiveness of the second application was related to the concentration applied and the date of the first spray. The relative increase in trunk-cross-sectional area was not affected by the growth inhibitor. No negative effects on yield and fruit quality were found except for a reduction of soluble solid content. Flower initiation in the following year was not affected. Concentrations of 100–200 mg l⁻¹ applied shortly after full bloom should be recommended, bearing in mind that a second application might be necessary 6–8 weeks later.     

The thinning effect of benzyladenine on red ‘Fuji’ apple trees

A trial, at the Grove Research Station in southern Tasmania, studied the thinning effect of benzyladenine (BA) on five year old red ‘Fuji’ apple trees. Untreated control trees were compared with trees treated at four timings, from full bloom (FB) to 30 d after full bloom (AFB), with four concentrations of BA (50, 100, 200 or 400 mg I-1). The most effective time of thinning was 20 d AFB, when increasing concentration also increased thinning. Further advantages of this successful thinning were reflected in better fruit size and weight. At 30 d AFB high concentrations of BA depressed fruit weight. Return bloom was improved significantly by both 20 and 30 d. AFB sprays with a concentration effect at 20 d AFB. Timing of sprays had no effect on the incidence of russet which was increased only by applications of 400 mg l-1. Both the higher concentrations and later timings resulted in an increase in shoot numbers and total growth. Reduction in mean shoot length was related more to the concentration of BA used than to differences in the timing of sprays. BA has shown potential as a thinner for red ‘Fuji’ apple at 20 d AFB.     

The interaction of Cytolin and NAA on cropping red ‘Delicious’ apple

A trial, at Spreyton in north-western Tasmania, studied the effects of Cytolin and NAA sprays on the thinning and shape of ‘Delicious’ apples. Untreated control and hand thinned trees were compared with trees treated with Cytolin or NAA alone, or in combination. Cytolin was applied at 25 mg 1~‘ at the king petal (KP) stage. NAA was applied at 8 mg I“1 at full bloom (FB) and 7,10, or 15 days after full bloom (AFB). Cytolin alone had no effect on thinning, fruit weight or on pip numbers but it did improve fruit shape. The combination of cytolin and NAA at FB overthinned. Cytolin and NAA combinations applied at all times after FB significantly decreased both mean fruit weight and pip numbers and reduced the percentage of fruit > 70 mm. All Cytolin-NAA combinations and the NAA treatments applied at 10 and 15 days AFB resulted in unacceptably high percentages of apples < 45 mm in diameter (pygmy fruit). It is recommended that Cytolin and NAA should not be used in the same spray programme. NAA alone is a most effective thinner at FB or seven days AFB.     

The influence of fungicides and gibberellin (A4+7) applications on russet control of ‘Golden Delicious’ apple fruit

Summary

Various fungicides, gibberellins (A₄₁₇) and their mixtures were tested for the control of russet of ‘Golden Delicious’ apple fruit in the major apple-growing area in Israel. Four foliar applications of captan, metiram, the strobilurins kresoxim-methyl, trifloxystrobin, azoxystrobin, or the polyoxin B compound Polar from the green tip stage to the end of the petal fall stage gave similar reductions in russeting, compared with the controls, but none eliminated it. Tank mixtures of the gibberellins (A₄₁₇) Regulex and Perlan with captan, each at full rate, did not improve russet control, compared with each component alone at the same rate. Similarly, both captan and trifioxystrobin, and the gibberellin (A₄₁₇) Cytolin or their mixtures at full rates provided similar significant level of control of russet on fruit. Fruit in the upper part of the tree had significantly more russet than fruit in the lower part of the tree, regardless of treatment applied. In addition, russet was more severe on fruits of trees grown in the west side of the row, than those of trees grown on the east side. Data suggest that factors other than fungicides, which may act by reducing russet-inducing microorganisms, may be involved in russet development.     

Nursery performance of ‘Cox’ apple trees with rootstocks of M.9 from either micropropagation or improved conventional propagation from micropropagated plants

Rootstocks of M.9 were produced either directly by micropropagation, by improved conventional propagation from apparently rejuvenated micropropagated plants or by conventional propagation throughout. These rootstocks were grown in the field for one year and then grafted with scions of ‘Cox’s Orange Pippin’. Performances of the composite trees were evaluated one year following grafting. Trees with rootstocks which came directly from micropropagation had many suckers and burrknots and usually had poorly developed scions. Trees with rootstocks from improved conventional propagation from micropropagated plants were similar to trees with rootstocks from conventional propagation throughout in being almost devoid of suckers and burrknots and having well developed scions.     

Analysis of S-alleles by PCR for determination of compatibility in the ‘Red Delicious’ apple orchard

Summary

In a previous study, the apple ‘Jonathan’ was shown to be semi-compatible with the ‘Topred’ sport of ‘Red Delicious’, the main cultivar in Israel. This incompatibility led to reduced pollination potency, explaining the low yield obtained from ‘Topred’ rows adjacent to ‘Jonathan’. Hence, the importance of identifying the level of compatibility for all ‘Topred’ pollinators became apparent. By analysing S-allele by PCR with primers for the various S-alleles of the cultivars in the ‘Topred’ orchard, including S10 and S28, which were cloned in this study, it was evident that apart from ‘Jonathan’, the common pollinators for ‘Topred’ are fully compatible with it. The ability to identify all S-alleles in the ‘Topred’ orchard was also utilized to resolve the observation that, although ‘Topred’ is considered self-incompatible, self-pollinated, net-caged, ‘Topred’ flowers set some fruit. Applying PCR-analysis of S-alleles to the progeny of the suspected self-pollinated ‘Topred’ fruit revealed that the fruit-set was the outcome of cross-pollination, perhaps the consequence of fertilization by wind carried pollen. Hence, the notion that ‘Topred’ is totally self-incompatible was confirmed and the efficiency of progeny PCR S-allele analysis for the determination of the pollen donor was exhibited.     

Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Summary

Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21 – 70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex^® Ca [10% (w/w) Ca] and Manni-Plex^® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex^® Ca plus Manni-Plex^® B remains to be elucidated.     

Effects of different rootstocks and training systems on the mineral composition of ‘Delicious’ apple leaves

Leaf mineral composition as affected by different rootstocks, cultivars, training systems and their combinations was measured during 1987 and 1988. Trees on M.7 had significantly higher concentrations of N, P and Fe, whereas those on MM. 106 maintained higher values of K, Ca, Mg and Mn during both years. Between cultivars, Red ‘Delicious’ showed greater accumulation of N, P, Mg and Fe but K and Cu levels were found to be more in Starking ‘Delicious’. All mineral nutrients except Ca and Mg accumulated more in spindle-bush trained trees than those under modified central leader system. The Mineral composition of Starking ‘Delicious’ grafted on M.7 rootstock and trained as a spindle bush produced the best yield efficiency and fruit quality, and fell within the normal range.     

The influence of endothal and 6-benzyladenine on crop load and fruit quality of red ‘Delicious’ apple

Summary

Trial work over a two year period examined the aquatic herbicide endothal as a blossom thinner in conjunction with 6-benzyladenine (CyLex?) as a post-bloom thinner. The aim was to develop an effective thinning programme using endothal and CyLex?, to examine any interactions between the two chemicals, and to assess the impact of endothal on fruit quality. Time of application of endothal was shown to be critical in achieving a satisfactory level of thinning. Multiple applications of lower chemical rates were also successful, and may have potential to provide an effective programme for cultivars with long flowering periods, which are traditionally most difficult to thin. Addition of a surfactant to the spray mix significantly increased the thinning effect of endothal, resulting in severe over-thinning. This work has demonstrated that endothal is an effective thinner of red ‘Delicious’ apples. It is most effective when applied twice during the blossom period, the first application at 20% bloom and the second at 80% bloom. There is no advantage in increasing the concentration above 1.0 cm³ dm^-3 (v/v). Endothal can also be effectively combined in a programme with the post-bloom thinner CyLex? applied at 150 mg l”¹ at a spray volume of 12001 ha^-1. Addition of CyLex? to the spray programme has the added benefits of increasing fruit weight and size. Fruit sugar content and firmness were both increased by application of endothal. The greater the number of applications the higher the firmness and sugar content of the fruit. Both these findings are additional benefits to the thinning effect. Both pip number and fruit length/diameter ratio were slightly reduced by endothal. Cylex and some endothal treatments increased the incidence of fruit russet.     

Pre-harvest drop control of ‘Red Delicious’ and ‘Jonathan’ apple (Malus domestica) as affected by the synthetic auxin 3,5,6-TPA

Summary

‘Red Delicious’, the main apple cultivar grown in Israel, and ‘Jonathan’, grown on a smaller scale, are prone to substantial pre-harvest drop. Spraying both cultivars with the synthetic auxin 3,5,6-trichloro-2-pyridyl-oxyacetic acid (3,5,6-TPA) reduced pre-harvest fruit drop and increased yield. Application of 40 mg l^–1 3,5,6-TPA 2 weeks before anticipated harvest (WBH), or 30 mg l^–1 3,5,6-TPA at 4 and 2 WBH gave the best results, and were as effective as 2,4,5-trichloro-phenoxypropionic acid (2,4,5-TP) which was the commercial product commonly in use until being withdrawn. There were no negative effects on fruit quality at harvest, or during 8 months of storage. Therefore 3,5,6-TPA can be recommended for routine use on ‘Red Delicious’ and ‘Jonathan’ apples in Israel.     

The effect of boron upon leaf development and growth of the apple cultivar ‘Cox’s Orange Pippin’

One-year-old ‘Cox’s Orange Pippin’ trees planted in pots in sand culture in the spring of 1970 were (during the growing seasons of 1970–72) watered with nutrient solutions containing 0, 0.12, 0.23, 1.2, 3.5 or 7.0 mg boron per litre.

With increasing boron supply, the boron concentration of the leaves increased, the growth of current year’s shoots and to some extent of other plant parts increased, and summer leaf-fall and the occurrence of necrotic leaf spots (‘Cox spots’) decreased. The percentage of healthy leaves was greatest when boron in leaf dry matter was about 30 ppm.

In 1972 the trees with highest boron supply suffered from incipient boron toxicity and increased incidence of ‘Cox disease’ flowering was delayed, and the percentage of dead buds was increased. In the latter part of the summer the leaves curled upwards, turned purple and became brittle.     

Girdling of early season ‘Mayfire’ nectarine trees

The effect of four times of limb girdling on fruit and tree response was examined on ‘Mayfire’ nectarine (Prunus persica (L.) Batsch). Girdling prior to Stage II of fruit growth reduced the lag phase associated with Stage II, and caused peak fruit growth rates to occur earlier in the season than on later girdled or ungirdled trees. Optimum response was obtained by girdling prior to Stage II, when fruit seed length was approximately 10 mm. Girdling at this time increased fruit weight by 22.5% and more than doubled the percentage of fruit in the largest three size categories. Maturity, measured as soluble solids concentration, was increased by 42%. Shoot extension growth was reduced only by early girdling. Leaf weight per unit area was increased, and leaf nutrient concentrations were decreased by all girdling treatments. Leaf conductance to water vapour (g,) was not affected when measured 8 days prior to and 78 days after harvest. Fifteen days after harvest, g, was decreased in all girdling treatments.     

Short-term effects of changes in soil management and nitrogen fertilizer application on ‘Bramley’s Seedling’ apple trees.

Soil managment in a ‘Bramley’s Seedling’ orchard, established in a system of herbicide treated tree rows and mown grass alleys, was changed to provide three treatments: complete grass cover, overall herbicide and a continuation of the existing system. Differential rates of N fertilizer (nil, 62.5 kg ha-1) were applied to each soil management regime. In comparison with herbicide strips, complete grass was intensely competitive, particularly with nil application of N fertilizer, reducing tree growth and yield and greatly decreasing leaf N. Leaves from trees in complete grass (nil N) plots contained higher concentrations of P, K and B but lower ones of Ca, Mn and Cu. Compared with the change from herbicide strip to complete grass management, effects of changing to overall herbicide were smaller. There were slight increases in leaf N concentration but no increases in tree growth or fruit yield. Leaf Mn concentration was increased in overall herbicide. Although application of N fertilizer to grass plots increased leaf N concentration by 0.4% and the three-year girth increment, yield was less than that of trees in herbicide strips. Nitrogen fertilizer applied to herbicide strips or overall herbicide plots slightly increased leaf N content but there was no effect on yield or girth increase. Applying N fertilizer to complete grass plots reduced the concentration of P, K and B in leaves but increased leaf Ca, Mn and Cu.     

Inflorescence bud growth,development and abscission in shoots of bearing and disbudded ‘Bianca’ pistachio trees

Summary

Dry-matter accumulation patterns and anatomical aspects of development and abscission of inflorescence buds borne on shoots of fruiting (BF) and non-fruiting (BNF) branches of bearing trees and in non-bearing branches of disbudded (NBD) pistillate trees of pistachio (Pistacia vera L.) were studied from the end of May to mid September. In NBD trees, inflorescence-bud summer drop was negligible and, by the end of the growing season, dry-matter content in NBD buds was three times higher than in BF buds. The anatomical investigation showed that the inflorescence buds, irrespective of their being on shoots of fruiting or not-fruiting branches, undergo the same differentiation process, which is completed by the end of spring. In June and July, signs of degenerations are detectable in the conducting tissue of the buds that will abscise. The degeneration seems to precede and, presumably, trigger the onset of abscission layers, which may develop in different points of the inflorescence. It is suggested that the event triggering the onset of the abscission process precedes the phase of rapid embryo development and that it might be ascribed to the embryo in the phase following the first zygotic division.     

Effect of part-tree flower thinning on fruiting,vegetative growth and leaf photosynthesis in ‘Cox’s Orange Pippin’ apple

Flower clusters were removed at full bloom from ten year old ‘Cox’s Orange Pippin’ trees on M.9 rootstocks, over the whole tree, on alternate branches or on whole sides. Mean fruit weight per tree at harvest was linearly dependent on leaf area per fruit and on light interception per fruit, both relationships accounting for over 90% of the variance. These relationships did not differ between treatments, implying either a mobile pool of carbohydrate or photosynthetic adjustment within the tree to crop load. Measurements of leaf photosynthesis in July and September showed no statistically significant differences in photosynthetic rate of spur or extension shoot leaves on bearing or non-bearing branches. Although the treatments caused no overall effects on shoot growth or leaf area per tree, sides of trees without fruit had greater leaf area and shoot growth than did sides bearing fruit. Fruit mineral composition and percentage dry weight were not affected by treatment except where the treatments significantly altered fruit size. In the following spring, although the treatments did not affect the total number of flower buds produced, branches that were deflowered in the previous spring carried significantly more flower buds than did branches which had cropped.     

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.     

Response of ‘Comice’ pear trees to a postharvest urea spray

A single postharvest urea spray at 5 and 10% increased nitrogen (N) content in one year old bark and wood and in the flower buds and blossoms in 1987. In 1988, there was also an increase in N in one year old bark and wood but not in the N content of flower buds and blossoms. Fruit set was not significantly increased in either year. Control trees were much taller in N in 1988 than they were in 1987 since additional soil N was applied. Urea labelled with 15N was applied to branches and individual spurs immediately after harvest. When the l5N-urea was applied to branches, the next season’s flower buds had 12% of their N derived from the fertilizer (NFF), but when urea was applied to individual spurs only 8% NFF was detected. Remobilization of labelled N from treated to adjacent spurs resulted in less NFF than would occur if all spurs on the same branch received labelled N. Flower clusters distal and basal to the spurs treated with labelled l5N showed considerable amounts (>60% of sprayed spur) of N from the labelled spray. However, harvest analysis of adjacent and distant spur leaves and fruits from treated spurs and branches revealed that urea was only locally mobilized in the tree. Nitrogen status can be altered with postharvest urea sprays but the response varies with the N status of the tree. Postharvest soil application of labelled N showed N movement into blossoms but not in the flower buds.     

Foliar applications of calcium do not impact on fruit and leaf nutrient concentration or quality of ‘O’Neal’ blueberry

Calcium (Ca) has been considered a key element in maintaining fruit quality and extending the storage period of several fruits. The main blueberry (interspecific hybrids of Vaccinium corymbosum x V. darrowii) market for the Southern Hemisphere production involves a long transport between harvest and consumption. Foliar Ca sprays during the pre-harvest constitutes a common practice for improving Ca concentration [Ca] in fruits and therefore in alleviating the loss of firmness, dehydration and rot decay during postharvest. In this study, two formulations of Ca; Ca-nitrate [Ca(NO₃)₂] and chelate Ca-oxide (Ca-gluconate; Ca-Glu) were sprayed four times during pre-harvest of blueberry cv. O’Neal. [Ca] in the fruits was followed after each application and fruit quality parameters were determined at harvest and during 28 days of cold storage. Both formulations were ineffective in increasing [Ca] in the berries (or leaves) after any of the four applications. In fruits, [Ca] decreased from 0.32% at 25 days after full bloom (DAFB) to 0.11% Ca at harvest time. Other minerals such as magnesium (Mg), potassium (K), or nitrogen (N) remained unaffected by the treatments. Data shows that foliar pre-harvest applications of Ca, regardless of formula, were ineffective at increasing [Ca] or improving the quality of the fruit.     

Regulated deficit irrigation in ‘Clementina de Nules’ citrus trees. II: Vegetative growth

Summary

An experiment on Regulated Deficit Irrigation (RDI) was performed during 1995 and 1996 in an orchard planted with drip-irrigated ‘Clementina de Nules’/Carrizo Citrange in Moncada (Valencia) Spain. Treatments consisted of a control, irrigated during the whole year at 125% ET_lys and RDI treatments where irrigation was reduced to 25% or to 50% of crop evapotranspiration measured by a weighing lysimeter (ET_lys) during one of the following periods: I) flowering and fruit set (spring); II) initial fruit enlargement phase (summer) and III) final fruit growth and maturation phases (end of summer-autumn). An additional treatment, denominated 50%-Year, was irrigated at 50% ET_lys during the whole year. The effects of RDI treatments in relation to tree water status (pre-dawn Ψ^pd and midday Ψ^md leaf water potential, as well as their integral with time) show a good relation between total shoot emergence in the different growth flushes and the stress intensity reached (Ψ^pd) (r² = 0.80). This correlation was mainly due to the number of floral shoots (r² = 0.86) and not to vegetative ones (r² = 0.22). Similar results were observed between the stress integral at pre-dawn in each period and the former sprouting variables. In all cases, correlation was better with pre-dawn leaf water potential or with pre-dawn stress integral than with those at midday. RDI during spring reduced shoot length of the first growth flush (A1) and increased fruitlet fall after restarting normal irrigation. It also produced “off-season” flowering in the second flush growth (A2) and increased shoot emergence of the third flush growth (A3) with about 10% of them being floral. Summer RDI treatments did not alter vegetative growth, and although they produced off-season flowering (A3) it was much smaller than that of autumn RDI treatments, which in addition reduced vegetative growth with respect to the control. These effects, together with those of yield and fruit quality presented elsewhere, show that summer is the more appropriate period to apply RDI in “Clementina de Nules” mandarin trees.     

Thinning ‘Red Fuji’ apples with ethephon or NAA

Summary

A series of trials in Tasmania examined the thinning effects of ethephon and NAA on ‘Red Fuji’ apple. In the ethephon trials, concentrations from 25 to 600 ppm were applied at full bloom (FB) or 14 days after full bloom (AFB) to trees on either seedling or M.M.106 rootstocks. The NAA trial involved spraying concentrations of 5, 10 or 15 ppm at FB or 14 days AFB to trees on seedling rootstocks. Ethephon thinning of ‘Red Fuji’ was similar at FB and 14 days AFB. The dependence of fruit thinning on ethephon concentration was described by fitting non-linear response curves. These relationships were stronger and less variable for M.M.106 than seedling trees. Ethephon proved a satisfactory thinner for trees on both rootstocks. At the high spray volume used, the preferred concentrations at both FB and 14 days AFB would be 25 or 50 ppm for seedling and 100 or 200 ppm for M.M.106 rootstocks. NAA under-thinned at 5 ppm and over-thinned at 10 and 15 ppm at both FB and 14 days AFB. No firm recommendation can be given for NAA as a thinner of ‘Fuji’ at this stage.