A comparison of high- and low-volume spray techniques in the thinning of ‘Golden Delicious’ apples

A trial at the Grove Research Station, southern Tasmania in 1989-90 examined the thinning of mature ‘Golden Delicious’ apple trees. High-volume sprays were applied at 6,0001 ha^-1 as air blast or vertical boom using NAA at 10mg l^-1 4d after full bloom (AFB) and 18 d AFB. Carbaryl at 1,000 mg l^-1 and thiram at 1200 mg l^-1 were also applied as combined sprays, 30 and 38 d AFB. These high-volume sprays were compared with unsprayed controls and Micron and Micronair low volume sprayers at 200 and 1,1000 l ha^-1. The dosages of the low volume applications were equilibrated to apply the same rates of chemical per hectare as the high-volume sprays, and the timing was the same. All spray treatments reduced crop load to acceptable levels when compared with the overcropped controls. There were no consistent differences between treatments for number of fruit per cm² limb area except that the lowest volume Micron spray thinned significantly less than most other treatments. Considering the number of fruit per 100 blossom clusters the airblast spray was the only treatment to be significantly better than the Micron at 2001 ha^-1. These numbers were reflected in mean fruit weight with the control fruit being significantly lighter than any sprayed fruit. The air blast treatment produced significantly heavier fruit than all other treatments, apart from the other high volume treatment. Fruit size distribution (FSD) showed significant differences between the control and all the spray treatments. The airblast treatment produced significantly more fruit in the 80 mm or larger category than all treatments, apart from the vertical boom application. These preliminary results suggest that although low-volume sprays can thin apple trees, the use of ultra low volumes (ULV) should be explored using machines capable of controlled droplet application (CDA). This may ultimately lead to less chemical being applied per hectare.     

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 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.     

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 effects of high CO2 pre-storage treatments and rate of establishment of controlled atmosphere conditions on bitter pit and bruise susceptibility of ‘Bramley’s Seedling’ apples

Summary

Bitter pit incidence in Bramley apples that were cooled prior to either slow (three weeks) or rapid (one day) establishment of controlled atmosphere (CA) conditions (9% CO₂, 12% O₂) was 14.7 and 3.2% respectively. Bruise susceptibility was also reduced by rapid CA establishment although the rate of fruit softening was unaffected. The control of bitter pit by pre-storage treatment with 15–25% CO₂ for one to three weeks was no better than by rapid establishment of CA, although bruise susceptibility was further reduced by some treatments. Some pre-storage treatments caused injury to the apple skin and flesh (brownheart). The extent to which fruits were injured was dependent on CO₂ concentration and the duration of CO₂ treatment. There was some evidence that early picked fruit not cooled prior to CO₂ treatment was more severely injured both internally and externally by CO₂ than that harvested later and cooled prior to treatment.     

The effect of selective picking on the harvest fruit size distribution of ‘Royal Gala‘ apples

Summary

The size distribution of fruit on an apple tree on any potential harvest date can be estimated by measuring a sample of fruit early in the season and projecting forward in time using standard growth curves. However, ‘Royal Gala‘ apples grown in New Zealand are picked in multiple harvests spread over about three weeks, so the overall size distribution of harvested fruit can differ significantly from that on any single harvest date. On each havest date, fruit are selected for picking according to background colour, not size. By measuring the sizes at harvest of all fruit on selected limbs of eight ‘Royal Gala‘ trees in Hawkes Bay, New Zealand, we show that the relationship between the size distributions of picked and unpicked fruit can be described by a single-parameter model. Although size is not used directly in fruit selection, we find that larger fruit still tend to be picked first, with the odds of a fruit being selected approximately doubling for each 20.g increase in size. The mean harvest fruit size is largest for the first harvest, and decreases in later harvests, despite ongoing fruit growth. Because the smaller fruit left on the trees continue to grow, the standard deviation of the overall fruit size distribution from multiple harvests can be expected to be significantly smaller than it would have been had all fruit been harvested on the same date. The model is tested using size and background colour measurements collected on tagged fruit at three sites in two years, including a range of shading and crop load treatments. For most combinations of site, year and treatment, the model predicted the size distribution of picked fruit well, but in a few cases a different parameter value was need to obtain a good fit.     

Hormonal control of splitting in ‘Nova’ mandarin fruit

Fruit splitting, a physiological disorder of peel development in citrus, has been studied in terms of peel thickness and puncturing resistance in ‘Nova’ mandarins. Both features are negatively correlated with splitting. A mixture of G A, and 2,4-D reduced significantly the percentage of affected fruits. The best results were obtained with two applications at 60 and 30 d before the anticipated onset of the disorder. Calcium nitrate applications have similar effects, but were ineffective in orchards with a low natural incidence of splitting.     

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.     

Effects of crop load and time of thinning on the incidence of split pits,fruit yield,fruit quality,and leaf mineral contents in ‘Andross’ peach

Summary

The effects of light, moderate, or heavy thinning (5, 10, or 20 cm between fruit, respectively), conducted before (7 d or 15 d), during, or after (7 d or 15 d) pit hardening (PH), on the incidence of split pits, fruit yield, fruit quality characteristics, and leaf mineral contents, were studied in the canning peach (Prunus persica L. Batsch.) cultivar ‘Andross’ over two growing seasons. The percentage of fruit with split pits increased by 58.2% in heavily-thinned trees compared with moderately- or lightly-thinned trees, and by 22.9% for the earliest time of thinning (15 d before PH) compared with thinning during, or after PH. Fruit fresh weight (FW) was greater in moderately- and heavily-thinned trees compared with lightly-thinned trees, but yields were similar among the different crop-load treatments. The latest time of thinning (15 d after PH) also had a negative impact on yield at first harvest and on total yield, fruit FW, and delayed fruit ripening compared to thinning during, and 15 d before PH. Total anti-oxidant capacities and phenolic contents were usually greater in fruit from heavily-thinned compared with lightly- or moderately-thinned trees only when thinning was conducted during, or 15 d after PH. Moreover, anti-oxidant levels were highest in fruit from the earliest-thinned trees. There was no significant effect of crop load, or of time of thinning application treatment on fruit colour, or on the K, P, Fe, Mn, and Cu contents of leaf tissues. In conclusion, light or moderate thinning during PH resulted in minimal split pits during processing, and in optimal yields and fruit quality characteristics in the canning peach cultivar ‘Andross’.     

Effects of light on flavonoid and chlorogenic acid levels in the skin of ‘Jonagold’ apples

The objective of our work was to determine how fruit position on the tree affects flavonoid and chlorogenic acid contents. Light was measured at different positions within the canopy of 10-year-old ‘Jonagold’ apple trees on M.9 rootstock raised as slender spindles. Fruit from the top of the canopy contained the highest percentage of blush and the highest levels of cyanidin 3-galactoside (anthocyanin) and quercetin 3-glycosides, followed by fruit from the outside of the canopy, and then those from the canopy interior. There were no significant differences in the levels of catechins, phloridzin and chlorogenic acid among fruit from the different canopy positions. Light level was directly correlated with the levels of cyanidin 3-galactoside and quercetin 3-glycosides and with the percentage of blush in the fruit skin. Light in the interior of the canopy was poorer in UV-A, blue, green and red but richer in far-red light than at all other positions. Consequently, the FR/R ratio was much larger at the interior of the canopy than at all other positions. Both anthocyanin and quercetin 3-glycoside concentrations were clearly related to light level, and there was a critical FR/R ratio of about 1 below which no anthocyanin and only minimal quercetin 3-glycosides were formed.     

Improvement of fruit quality and storage potential of ‘Braeburn’ apple through deficit irrigation

Summary

We explored the potential of deficit irrigation (DI) applied at different times during the growing season for improving fruit quality and storage potential of ‘Braeburn’ apple growing in a commercial orchard. Because DI often reduces fruit size, effects of fruit size on fruit quality were also examined. The irrigation treatments were: commercially irrigated control (C), early deficit irrigation (EDI) applied from 63 to 118 d after full bloom (DAFB), and late decifit irrigation (LDI) applied from 118 DAFB to final harvest on 201 DAFB. Both EDI and LDI improved fruit quality in terms of increases in: dry-matter concentration (DMC) at harvest, flesh firmness, total soluble solids, and total soluble sugars both at harvest and after storage. The DI fruit had less weight loss during storage than did C fruit. Deficit irrigation affected the concentrations of a few individual aroma volatiles but not total volatile concentration. Incidence of physiological disorders was not affected by irrigation treatments. Mean fruit weight was lower in DI than in C but the difference was not significant. Among the quality attributes studied, only firmness and DMC were affected by fruit size with their values being higher in smaller fruit.     

Comparison of sampling strategies for determining fruit mineral concentrations in ‘Hass’ avocado (Persea americana Mill.)

Summary

Spatial and temporal variation in mineral and dry matter (DM: % dry weight) concentrations were examined in ‘Hass’ avocado (Persea americana Mill.) fruit to identify sampling strategies for examining fruit mineral, DM and fruit quality relationships. Calcium (Ca), magnesium (Mg), potassium (K), and DM concentrations were compared from different parts of the same fruit, from fruit harvested from different shoot types and locations within the same tree, and at different stages during the growing season, from fruit set to commercial harvest. The main source of variation within fruit was longitudinal, with K and DM concentrations being higher at the distal end of the fruit. Sampling methods based on equatorial plugs of tissue provided the best estimates of whole fruit values for DM and mineral nutrients. While there was much variability in the internal distribution of minerals within the fruit, the distribution was the same for fruit from both the northern and southern aspects of the tree. During the first 4 months after fruit set, fruit from determinate floral shoots (i.e., with a flower in the terminal position) had higher Ca and Mg concentrations than fruit from indeterminate shoots (i.e., with a shoot in the terminal position). After this time, fruit Mg and Ca concentrations were higher on indeterminate shoots, possibly because of changes in sink-strength and increased transpirational flow associated with new leaf growth on indeterminate shoots. The data showed that shoot type was a source of fruit-tofruit variability in an avocado crop, and that care should be taken in sampling fruit tissues for nutrient analyses.     

Effect of calcium supply on the physiology of fruit tissue in ‘Andesu’ netted melon

Summary

Fruit development and physiological traits were evaluated in ‘Andesu’ netted melon plants grown with and without calcium. Calcium exclusion accelerated softening, alcoholic fermentation and ethylene evolution of fruit compared with those supplied with calcium, but the opposite trend occurred with sucrose accumulation. A significant difference of calcium concentrations in the fruit between treatments was observed at the developing stage of the fruit (P<0.05), but the difference became smaller as fruit matured. In the mesocarp tissue from the basal hemisphere, calcium concentrations in the NaCl soluble fraction at ripe fruit stage differed significantly (P<0.05) between calcium treatments but no significant difference was detected in the inner mesocarp of the distal hemisphere. Calcium exclusion did not lead to the development of water-soaked symptoms in the mesocarp tissue of ripe fruit. Uronic acid concentrations in ionically bound pectin fraction did not differ between calcium treatments throughout fruit development. In covalently-bound pectin fraction, however, uronic acid concentration of ripe fruit was significantly lower in calcium-excluded plants than in calcium-supplied plants (P<0.05). Our results suggest that: first, accelerated fruit softening under calcium deficient conditions might result from promoted ethylene evolution rather than from the shortage of ionically-bound calcium in cell walls, second, calcium deficient condition does not necessarily lead to water-soaked symptoms in tissue of ‘Andesu’ melon fruit.     

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.     

Preharvest applications of ethephon reduce superficial scald of ‘Fuji’ and ‘Granny Smith’ apples in storage

In 1989 and 1990, preharvest applications of 2-chloroethyl phosphonic acid (ethephon) at dosages from 50–400 mg 1’1 were applied to ‘Fuji’ and ‘Granny Smith’ apples. In 1989, the greatest reduction in scald after storage on both ‘Fuji’ and ‘Granny Smith’, relative to the untreated control resulted from applying 400 mg 1^?1 ethephon five weeks before harvest and was 45% and 55% of controls, respectively. On ‘Granny Smith’ 400 mg 1^? was also effective when applied three weeks before harvest. In 1990, preharvest applications of ethephon at either 200 or 400 mg 1^?1 reduced scald in both cultivars relative to the controls. Ethephon applied six weeks before harvest had no dosage effect on scald reduction after storage. There was no consistent effect on fruit maturity at harvest from any treatment in either year, and no effect on quality of fruit out of storage.     

Response of the phenylpropanoid pathway to Venturia inaequalis infection in maturing fruit of ‘Braeburn’ apple

Summary

This study investigated the activities of key enzymes in the phenylpropanoid pathway and the accumulation of phenolic products in apple peel in response to infection with Venturia inaequalis [(Cooke) G. Wint.]. We compared healthy apple peel with apple peel showing symptomatic scab lesions, and with peel tissue from 1 – 2 mm around the scab lesions in fruit 1 month before maturity [140 d after full bloom (DAFB)] and at physiological maturity (175 DAFB). Infection with V. inaequalis enhanced the synthesis of some phenolic compounds. Compared to healthy peel, scab lesion tissue had ≤ 3.1-times higher hydroxycinnamic acid content, ≤ 1.3-times higher dihydrochalcone content, and ≤ 3.9-times higher flavan-3-ol content. Scab lesions showed slightly higher phenylalanine ammonia-lyase, chalcone synthase, chalcone isomerase, flavonol synthase, and dihydroflavonol 4-reductase activities. The total amount of phenolics remained relatively stable between the two sampling dates, except for epicatechin and caffeic acid which decreased in amount toward fruit maturity, and levels of catechin which increased in more mature fruit. During fruit maturation, only chalcone synthase and chalcone isomerase activities decreased in all tissues examined. This study showed that the phenylpropanoid pathway in apple fruit peel changed significantly following infection with the apple scab pathogen.     

Preliminary trials to examine the effects of ethephon as a thinner of ‘Gala’ and ‘Jonagold’ apples

Trials in southern Tasmania examined the thinning effects of ethephon on ‘Gala’ and ‘Jonagold’ apples. Untreated controls were compared with ethephon thinning sprays applied at full bloom at 50,100,200,400,800 and 1 600 mg I“1 to both cultivars. Thinning of both cultivars was related to the concentration of the spray and in most cases logistic models were fitted. Thinning effectiveness was largely reflected in increased fruit weight and size. The ‘Gala’ fruit was still not large enough for Australian markets. Ethephon at 200 mg I“1 effectively thinned ‘Jonagold’ and produced the required increases in fruit size and weight. ‘Jonagold’ was overthinned by the high concentrations of ethephon, but this was not reflected in increased fruit weight and size. Ethephon also reduced vegetative growth at the higher concentrations which was considered an advantage. More work is required to establish specific recommendations for either cultivar.     

Manipulating Regular Bearing in ‘Golden Delicious’/M9 Apple Trees using GA4+7 and Ethephon

Control of regular cropping in apple is considered critical for fruit growers to ensure their economical sustainability. Irregular flowering can be mitigated by plant growth regulators thanks to their promotion or inhibition effects. In this study, responses of GA₄₊₇ and ethephon on alternate bearing in ‘Golden Delicious’/M9 were examined. GA₄₊₇ and ethephon were applied on the same trees during three consecutive years (2010–12). Flowering, yield, shoot growth, and also some fruit quality parameters were assessed. GA₄₊₇ appeared to be more effectual to regulate alternate bearing. The alternate bearing index calculated with yield in successive years was high in control (0.91), moderate in ethephon (0.71), and low in GA₄₊₇ treated trees (0.41). Modified alternate bearing index, based on cluster number, indicated moderate intensity in GA₄₊₇ (0.53) and high intensity in the others. Although GA₄₊₇ reduced crop density at about 50%, there was little variation in yield per tree and crop efficiency due to increasing of fruit size. GA₄₊₇ did not increase shot length after establishment of equilibrium between vegetative and generative growth in 2012. Ethephon slightly reduced vegetative growth and relatively increased fruit size due to the decrease of fruit set.     

Development of hypo-allergenic apples: silencing of the major allergen Mal d 1 gene in ‘Elstar’ apple and the effect of grafting

Summary

Many people who are allergic to birch pollen are also allergic to apple fruit, due to cross- allergenicity. Since apples are the most extensively consumed fruit in Europe, it is highly relevant to develop a hypo-allergenic apple.Apples with significantly reduced levels of the allergen, Mal d 1, may allow many apple allergics to eat them without an allergic reaction. We are currently collaborating to develop a hypo-allergenic apple within the European Integrated Research Project, ISAFRUIT (www.isafruit.org). Hypo-allergenic apple plants (Malus × domestica Borkh., ‘Elstar’) with decreased levels of Mal d 1 mRNA were produced by RNA interference (RNAi) technology. Ten genetically modified (GM) apple lines were selected. In vitro plantlets were first transferred to a greenhouse, then grafted onto wild-type M.9 rootstock to promote the development of fruit-producing trees. Levels of Mal d 1 gene silencing were measured repeatedly by quantitative real-time PCR. Compared to leaf samples from wild-type ‘Elstar’, two GM lines showed modest levels of gene silencing (up to 250-fold), whereas the other eight GM lines were significantly silenced (up to10,000-fold) in Mal d 1 gene expression. These levels of silencing were unaffected by grafting, and have been stable over more than 3 years, and throughout all developmental stages.