D After Full Bloom Research Articles

Optimizing Fruit-Thinning Strategies in Peach (Prunus persica) Production

Fruit size is a highly valued commercial trait in peach. Competition among fruit and among other sinks on a tree reduces potential growth rate of the fruit. Hence, crop-load management strategies such as thinning (removal of flowers or fruit) are often practiced by growers to optimize fruit size. Thinning can be performed at bloom or during early fruit development and at different intensities to optimize fruit growth responses. Responses to thinning may be cultivar and location specific. The objective of the current study was to fine-tune thinning strategies in the southeastern United States, a major peach producing region. Timing and intensity of thinning were evaluated across multiple cultivars over three years. Thinning at bloom or at 21 d after full bloom (DAFB) improved fruit size in comparison to unthinned trees in ‘Cary Mac’ and ‘July Prince’, respectively, in one year. Bloom-thinning reduced fruit yield (kg per tree) in the above cultivars in one year, suggesting that flower thinning alone may not be a viable option in this region. Intensity of thinning, evaluated as spacings of 15 cm and 20 cm between fruit, did not differentially affect fruit weight or yield. However, fruit diameter decreased quadratically with increasing fruit number per tree in ‘Cary Mac’, ‘July Prince’ and ‘Summer Flame’. Similarly, fruit weight decreased quadratically in response to increase in fruit number per tree in ‘Cary Mac’ and ‘July Prince’. Further, yield-per-tree decreased with increasing fruit size in ‘Cary Mac’ and ‘July Prince’. Importantly, these relationships were cultivar specific. Together, the data suggest that achieving a target fruit number per tree is an effective strategy for crop-load management to optimize fruit size in southeastern peach production. The target fruit number per tree may potentially be achieved through a combination of flower and fruit-thinning during early fruit development. Such an approach may provide flexibility in crop-load management in relation to adverse weather events.

Double-sided battle: The role of ethylene during Monilinia spp. infection in peach at different phenological stages

Controversy exists on whether ethylene is involved in determining fruit resistance or susceptibility against biotic stress. In this work, the hypothesis that ethylene biosynthesis in peaches at different phenological stages may be modulated by Monilinia spp. was tested. To achieve this, at 49 and 126 d after full bloom (DAFB), ethylene biosynthesis of healthy and infected ‘Merryl O'Henry’ peaches with three strains of Monilinia spp. (M. fructicola (CPMC6) and M. laxa (CPML11 and ML8L) that differ in terms of aggressiveness) was analysed at the biochemical and molecular level along the course of infection in fruit stored at 20 °C. At 49 DAFB, results evidenced that infected fruit showed inhibition of ethylene production in comparison with non-inoculated fruit, suggesting that the three Monilinia strains were somehow suppressing ethylene biosynthesis to modify fruit defences to successfully infect the host. On the contrary, at 126 DAFB ethylene production increased concomitantly with brown rot spread, and values for non-inoculated fruit were almost undetectable throughout storage at 20 °C. The expression of several target genes involved in the ethylene biosynthetic pathway confirmed that they were differentially expressed upon Monilinia infection, pointing to a strain-dependent regulation. Notably, Prunus persica 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) (PpACS) family was the most over-expressed over time, demonstrating a positive ethylene regulation, especially at 126 DAFB. At this phenological stage it was demonstrated the ability of Monilinia spp. to alter ethylene biosynthesis through PpACS1 and benefit from the consequences of an ethylene burst likely on cell wall softening. Overall, our results put forward that infection not only among different strains but also at each stage is achieved by different mechanisms, with ethylene being a key factor in determining peach resistance or susceptibility to brown rot.

Lycopene andβ-carotene content during growth of ‘Manee-Esan’ pummelo (Citrus grandis(L.) Osbeck) fruit

'Manee-Esan' is a new promising pummelo cultivar of the northeast of Thailand. This cultivar was locally found in the orchard at Baan Bung 14 Tambon Nonthong, Amphoe Kasetsomboon, Chaiyaphum province in the northeast of Thailand. The flesh of this cultivar has an attractive deep red color. It is believed that it is rich in antioxidants, especially lycopene and β-carotene. The taste of the fruit is sweet with a slight acidity. However, there was no scientific information supporting its quality, especially its harvest maturity. The research that was conducted was given the name: “Production System of Quality Pummelo for Identifying Creation of Chaiyaphum Pummelo” and was supported by the Thailand Research Fund and Khon Kaen University during 2015-2017. It was conducted to determine the content of lycopene and β-carotene, as well as the total soluble solid and total titratable acidity during fruit growth. The results showed that during fruit growth between 150-300 d after full bloom (DAFB), the content of lycopene, β-carotene, and the total soluble solid gradually increased (2.75-8.65 mg 100 g-1 FW, 0.90-2.55 mg 100 g-1 FW and 9.89-10.34%, respectively) while the Hue angle, titratable acidity and pulp firmness gradually decreased (42.67-20.64, 1.32-0.66% and 54.13-17.77 N cm-2, respectively). Lycopene and β-carotene reached the maximum content on the 270th DAFB (8.65 and 2.55 mg 100 g-1 FW, respectively) and no significantly decrease on the 300th DAFB (7.13 and 2.31 mg 100 g-1 FW, respectively). The total soluble solid content reached the maximum (10.34%) on the 240th DAFB, there was nog no significant decrease on the days that followed (10.26 and 10.17%). The top most ratio of TSS/TA (15.54) was also found on the 270th DAFB followed by the second most ratio on the 240th DAFB (14.98). However, the granulation of the pulp was found on the 270th DAFB. It should be concluded that to have a good taste and high content of lycopene, β-carotene and total soluble solids, 'Manee-Esan' pummelo should be harvested at 240th DAFB.

Prohexadione-Ca and Ethephon Suppress Shoot Growth of Sweet Cherries (P. Avium)

A 3-yr orchard study was conducted on Tehranivee, an advanced selection of sweet cherry [Prunus avium (L.) L.] on Mazzard and Gisela 6 rootstocks, to determine the efficacy of different prohexadione-calcium (P-Ca) and ethephon (ETH) treatments on vegetative growth. In experiment 1, cherry trees were treated with 123 or 246 mg L−1 P-Ca, which was sprayed on 16 and 30 d after full bloom (DAFB) or 16, 30, and 44 DAFB. In experiments 2 and 3, trees were treated before (−6 DAFB) and after (7 and 24 DAFB) bloom with P-Ca and rates similar to experiment 1, as well as with tank-mixed sprays of 123–246 mg L−1 P-Ca and 175 mg L−1 ETH applied at various timings. P-Ca alone or in combination with ETH decreased the vegetative shoot growth by up to 74% compared with the untreated control, but this varied by cultivar and year, as well as by plant growth regulator application rate, frequency, and timing. Lower rates of P-Ca at 123 mg L−1 were as effective as 246 mg L−1. No benefit was observed in applying P-Ca before blo...

Changes in Dormant Phase and Bud Development of ‘Fuji’ Apple Trees in the Chungju Area of Korea

Abstract: In this study, we investigated the onset and release of endo-dormancy under natural conditions by observing bud break characteristics in ‘Fuji’ apple trees using water cuttings. Through examinations of bud break rate and days to bud break, we found that the endo-dormancy of ‘Fuji’ apple tree continues for 70 d from 165 to 255 d after full bloom (DAFB), from late October to early January of the following year. In addition, within 20 d of first bud break, based on a final bud break rate of 60% or more, we able to identify the timing of the changeover from para-dormancy to endo-dormancy, and endo-dormancy to eco-dormancy. Analysis of the chilling requirement during the endo-dormancy period revealed that chilling accumulation up to 255 DAFB to release endo-dormancy amounted to 666 and 517 h based on the CH and Utah models, respectively. Observation of internal changes in the bud during endo-dormancy showed that flower bud differentiation begins from mid-July a, nd time of inflorescence of the disk flower is available to find. The flower buds subsequently developed slowl y but steadily during endo-dormancy and in the following year in February, the developmental stage of each organ had pro gressed. Moreover, the flower buds of ‘Fuji’ apples were mostly healthy during the dormancy period, but some exhibited necrosis of flower primordium, due partial cell damage from the formation of ice crystals rather than a direct effect of the low tempera ture. Flower buds were formed in both the axillary buds of bourse shoots and terminal buds of spurs, but lower bud differentiation was observed for the terminal buds of spurs at rate of about 65% of total buds, which was directly related to the bud size and shoot diameter.Additional key words:

Effect of plant growth regulators on calyx abscission, fruit quality, and auxin-repressed protein (ARP) gene expression in fruitlets of ‘Dangshansuli’ pear (Pyrus bretschneideri Rehd.)

SummarySepals of a pome fruit flower are collectively called the calyx. Calyxes may be shed to produce calyx-shed fruit (CSF), or remain to produce calyx-persistent fruit (CPF). To investigate the relationship between calyx shedding and phytohormone concentrations in fruitlets and fruit quality in ‘Dangshansuli’ pear (Pyrus bretschneideri Rehd.), endogenous levels of gibberellins, indole-3-acetic acid, abscisic acid, and zeatin riboside were measured in CSF and CPF at different stages of development. Manual excision of the calyx at an early stage of fruitlet development was also performed. The auxin-repressed protein gene (ARP) was cloned, and relative levels of ARP gene expression were determined in fruitlets on trees treated by spraying separately with water (control) or each of the plant growth regulators (PGRs) gibberellic acid (GA3), paclobutrazol (Pac), or 1-naphthaleneacetic acid (NAA) using real-time quantitative reverse transcription-PCR. The results indicated that manual calyx excision at an early stage of fruit development altered only the shape and appearance, but not the inner quality of the fruit. Higher endogenous levels of all gibberellins in fruitlets at 10 - 20 d after full bloom (DAFB) played an important role in calyx persistency on fruitlets. The ARP gene was cloned from fruitlets of ‘Dangshansuli’ pear and named PbARP. The full-length cDNA was 707 bp with a 5'-untranslated region (UTR) of 40 bp, a 3'-UTR of 316 bp, and a coding region of 351 bp, encoding a deduced polypeptide containing 116 amino acids.GA3 [100 mg l-1 of 90% (w/w)] inhibited expression of the PbARP gene and increased calyx persistency, whereas 100 mg l-1 of 15% (w/w) Pac enhanced PbARP gene expression and accelerated calyx shedding. Higher levels of PbARP gene expression in fruitlets of ‘Dangshansuli’ pear were associated with calyx shedding.The percentage of CSF increased by > 20% following treatment with 100 mg l-1 of 15% (w/w) Pac, 100 ml l-1 of an emulsifiable concentrate of 40% (w/v) flusilazole (Fls), a mixture of 100 mg l-1 of 15% (w/w) Pac plus 50 mg l-1 of 99% (w/w) benzylaminopurine (BA), or a mixture of 100 ml l-1 of 40% (w/v) Fls plus 50 mg l-1 of 99% (w/w) BA, with no significant difference in fruit set percentage or fruit quality. Persistence or shedding of the calyx in pear fruit is therefore an epigenetic trait that can be regulated by the application of PGRs.

Relationship between the bagging microenvironment and fruit quality in ‘Guibao’ peach [Prunus persica (L.) Batsch

SummaryThe late-ripening peach [Prunus persica (L.) Batsch] cultivar ‘Guibao’ was chosen in order to study the effect of different bagging treatments on the appearance, skin quality, and internal quality of fruit. Diurnal variations in temperature and relative humidity (RH) in white single-layer paper bags (WPB), white single-layer polypropylene non-woven bags (WPPB), and black single-layer paper bags (BPB) were recorded for 15 d before harvest. Bagging treatments were applied 30 d after full bloom (DAFB). The WPB and WPPB treatments continued until harvest, while the BPB were removed 7 d before harvest. Observations were recorded on skin colour and fruit quality attributes such as fruit fresh weight (FW), flesh firmness, total soluble solids concentration (TSSC), colour, skin pigments, soluble sugar concentrations (SSC) and organic acid concentrations. The average temperature and RH increased slightly in the bags. Compared with unbagged control fruit, the average temperature in WPB, WPPB, and BPB increased by 1.27%, 0.90%, and 0.04%, respectively. The RH in the same three types of bag also increased by 5.07%, 4.09% and 7.30%, respectively. Bagging led to higher mean fruit FW and skin lightness values. No significant differences were observed in peel anthocyanin or chlorophyll concentrations between the WPB and WPPB treatments, while the red colour saturation scale (a*) and chroma (C) values increased in the three types of bags. Anthocyanin concentrations in the peel of fruit from the BPB treatment increased rapidly to 44.52 nmol g-1 FW after bag removal. Both white bags had similar effects on fruit FWs, skin colour, pigment concentrations, and anti-oxidant capacity, as well as SSC and organic acid concentrations, but not TSSC and C values. The temperature and RH microenvironment in the bags could affect the rates of transpiration and respiration, with significant effects on SSC values. Based on these results, to obtain ‘Guibao’ peach fruit with an attractive skin appearance and good internal qualities, we recommend that fruit should be covered with bags and, if BPB are used, the bags should be removed 7 d before harvest.

Repeated applications of CPPU on highbush blueberry cv. Duke increase yield and enhance fruit quality at harvest and during postharvest

Applications of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) can increase blueberry (Vaccinium corymbosum L.) yield and fruit size, but their impact on postharvest is unknown. We studied repeated CPPU applications effects on yield and quality (harvest, postharvest), over 2 yr on mature 'Duke' plants in South-Central Chile. The first year, 5 or 10 mL L-1 CPPU was applied at 3, 10, and/or 17 d after full bloom (DAFB) plus a non-sprayed control. The second year, 5 or 10 mL L-1 CPPU were sprayed 10 and 17 DAFB plus a control. The first year, only 10 mL L-1 CPPU sprayed 3+17 DAFB increased yield (32.5% > control); 10 mL L-1 CPPU applied 10 or 3+17 DAFB had highest fruit diameter; and 10 mL L-1 CPPU at 17 DAFB or at 3+10+17 DAFB had highest soluble solids. Overall, 10 mL L-1 CPPU applied 3+17 DAFB, was the best treatment for year one, since it increased fruit yield and diameter, while soluble solids and postharvest weight loss were similar to control. The second year, 10 mL L-1 CPPU reduced fruit coloration (blue color coverage index: BCCI) and soluble solids, but not firmness at harvest. This rate increased berry weight (24.2%) and fruit wax (59% > wax coverage index: WCI) at harvest. Harvest and postharvest WCI increased consistently as CPPU rate increased. CPPU reduced fruit rotting (15% at 45+5 evaluation). During storage, CPPU-treated-fruit had a slower decrease in firmness (30.5% < control at 30+1), but no difference at 30+5. CPPU-treated-fruit usually had higher post harvest soluble solids. Ten mL L-1 CPPU retarded color evolution at harvest and at 30+1, but not at 30+5, 40+1 or 40+5.

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

SummaryLosses 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.

Manipulation of fruit dry matter accumulation and fruit size in ‘Scifresh’ apple through alteration of the carbon supply, and its relationship with apoplastic sugar composition

SummaryThe supply of carbon to fruit on whole apple trees of ‘Scifresh’ grafted onto M.9 rootstock was altered by adjustment of the crop load [43% removal at 60 d or 90 d after full bloom (DAFB)], by three periods of 75% shading (from 60 – 90, 90 – 120, or 60 – 120 DAFB), or by a combined treatment of fruit removal at 60 DAFB and shading from 60 – 120 DAFB. Altering the timing and duration of shading, and crop load adjustment, resulted in changes in fruit dry matter concentration (DMC), with a range at harvest from 14.0 – 17.5%. Thinning to reduce the crop load enhanced fruit DMC, with greater effects on both fruit DMC and mean fruit fresh weight the earlier it was done. Shading reduced fruit DMC, with greater reductions the longer the shade was left over the trees. All treatments had greater effects on fruit DMC and fruit quality (flesh firmness and soluble solids concentration) at harvest than on mean fruit fresh weight. This trial also provided fruit samples for measurements of both the carbohydrate content and apoplastic composition of cortical tissues. Starch contents and total apoplastic sugar concentrations were increased by reductions in crop load and were decreased by shading, with starch content being the most responsive. Apoplastic sugar concentrations increased during fruit development. The relative order of abundance of sugars in the apoplast and in the symplast plus vacuole was similar, although differences in the ratios of sugars were evident, with sorbitol accounting for ≤ 10% of the total sugar content in the apoplast and ≤ 3% in the symplast plus vacuole. This work has revealed the possibility of using apoplastic sugar concentration as an indicator of the carbohydrate supply to apple fruit.

Reducing the incidence of calyx cracking in ‘Pink Lady’ apple using a combination of cytokinin (6-benzyladenine) and gibberellins (GA4+7)

SummaryCalyx cracking in ‘Pink Lady’ apple (Malus × domestica Borkh.) results in substantial economic losses. ‘Pink Lady’ apple trees were sprayed with various rates and combinations of synthetic gibberellins (GA3, or GA4 plus GA7) and a synthetic cytokinin (6-benzyladenine; BA) at different phenological stages, starting at 60 d after full bloom (DAFB) until 150 DAFB, to determine if the incidence of cracking could be reduced. The experiments were conducted in Northern Israel between 2008 – 2011. The percentages of fruit with calyx cracking decreased following three applications of 0.2% (v/v) Superlon™ (i.e., 40 mg l–1 BA plus 40 mg l–1 GA4+7) at 14 d intervals, starting at 60 DAFB. GA3 or GA4+7 alone had no effect on cracking. In addition, the Superlon™ treatments resulted in increases in epidermal cell density at the calyx end, which may have contributed to the increased elasticity of the peel, thus preventing crack formation. No change was observed in cuticle thickness. Fruit quality was not affected by 0.2% (v/v) Superlon™ at harvest, or after 5 months of controlled atmosphere (CA) storage. However, fruit size increased, probably due to the effect of BA. The results from semi-commercial multiple applications of 0.2% (v/v) Superlon™ supported its use in orchards of ‘Pink Lady’ that tend to suffer from calyx cracking.

Reducing the incidence of calyx cracking in ‘Pink Lady’ apple using a combination of cytokinin 6-benzyladenine and gibberellins (GA4+7)

SummaryCalyx cracking in ‘Pink Lady’ apple (Malus × domestica Borkh.) results in substantial economic losses. ‘Pink Lady’ apple trees were sprayed with various rates and combinations of synthetic gibberellins (GA3, or GA4 plus GA7) and a synthetic cytokinin (6-benzyladenine; BA) at different phenological stages, starting at 60 d after full bloom (DAFB) until 150 DAFB, to determine if the incidence of cracking could be reduced. The experiments were conducted in Northern Israel between 2008 – 2011. The percentages of fruit with calyx cracking decreased following three applications of 0.2% (v/v) Superlon™ (i.e., 40 mg l–1 BA plus 40 mg l–1 GA4+7) at 14 d intervals, starting at 60 DAFB.GA3 or GA4+7 alone had no effect on cracking. In addition, the Superlon™ treatments resulted in increases in epidermal cell density at the calyx end, which may have contributed to the increased elasticity of the peel, thus preventing crack formation. No change was observed in cuticle thickness. Fruit quality was not affected by 0.2% (v/v) Superlon™ at harvest, or after 5 months of controlled atmosphere (CA) storage. However, fruit size increased, probably due to the effect of BA. The results from semi-commercial multiple applications of 0.2% (v/v) Superlon™ supported its use in orchards of ‘Pink Lady’ that tend to suffer from calyx cracking.

Modelling of weather parameters to predict russet on ‘Golden Delicious’ apple

SummaryRusset on ‘Golden Delicious’ apple (Malus × domestica Borkh.) fruit is a physiological disorder that causes major economic losses to growers. Large variations occur in the severity of russet from one year to another. In Girona (Spain), good correlations were found between the annual severity of russet at harvest and several weather parameters measured shortly after full bloom. A specific statistical methodology for the analysis of compositional data (CoDa) was used to establish these correlations. The most important factor was the percentage of time at relative humidity values > 55% from 30 – 34 d after full bloom (DAFB), which yielded a high correlation (R = 0.80). The percentage of rainy days from 0 – 34 DAFB was also positively correlated with the severity of russet (R = 0.80). Ordinal logit regression models that included these two climatic variables strongly predicted a low, moderate, or high annual severity of russet. Understanding the effects of weather on russet, and developing predictive models may help to manage the marketing of this apple variety which is prone to russet in some areas of cultivation.

Effect of the timing and duration of downward bending of branches on growth and fruit quality in ‘Fuji Mishima’ apple trees

SummaryA study was conducted to determine the most appropriate time, and hence duration of bending branches on 3-year-old ‘Fuji Mishima’ apple (Malus × domestica Borkh.) trees to control vegetative growth as well as to improve light penetration and fruit yield. Branches of ‘Fuji Mishima’ apple trees were tied-down at an angle between 120° – 150° from the axis of the tree trunk 0, 15, 30, and 45 d after full bloom (DAFB). The most appropriate time for branch bending was 15 DAFB in terms of reducing tree vigour, increased light penetration, and crop density. Bending at 30 or 45 DAFB caused vegetative tree growth similar to that in untreated trees, resulting in less flower bud development in the subsequent season.

Growth and fruit production in young ‘Fuji’ apple trees as affected by time of downward bending of branches

SummaryThis study investigated the most appropriate time of bending of all branches longer than 30 cm on 2-year-old ‘Fuji KIKU®8’ apple (Malus × domestica Borkh.) trees to control tree vigour, improve light interception, and enhance fruit yield efficiency in a commercial orchard in South Korea in 2004 and 2005. Branches of ‘Fuji’ apple trees were tied down at angles between 120º – 150º from the central leader of each tree –15, 0, 15, 30, 45, 60, or 75 d after full bloom (DAFB) in 2004. The most appropriate time for branch bending in terms of reducing tree vigour and increasing the number of flower buds and crop density was shown to be 15 DAFB. Trees with branches bent on 0 DAFB had significantly higher levels of light interception in August than the other bending treatment trees, in both years.

Expression analysis of the DkNCED1, DkNCED2 and DkCYP707A1 genes that regulate homeostasis of abscisic acid during the maturation of persimmon fruit

SummaryTo reveal details of the role(s) of abscisic acid (ABA) during fruit ripening and the regulation of ABA levels, two 9-cis-epoxycarotenoid dioxygenase genes (DkNCED1 and DkNCED2) and the DkCYP707A1 gene for ABA 8'-hydroxylase were isolated from unripened persimmon fruit. Expression of DkNCED1 increased at the start of fruit maturation and peaked 20 d before harvest, which was consistent with the accumulation of ABA during ripening in persimmon. Expression of the DkNCED2 gene was high in fruit at the immature stage, then declined continuously throughout ripening. Compared to the DkNCED genes, expression of DkCYP707A1 peaked 145 d after full-bloom (DAFB), then declined. Ethylene release decreased gradually from 65 DAFB to 115 DAFB, then peaked at 10 d after harvest. Water-deficit stress enhanced the expression of DkNCED1, but down-regulated transcript levels of DkCYP707A1 in the calyx. These results suggest that endogenous ABA content is modulated by a dynamic balance between ABA biosynthesis and catabolism, which is regulated by expression of the DkNCED1 and DkCYP707A1 genes, respectively, during persimmon fruit development and under drought stress.

Evaluating the effectiveness of different strategies for calcium application on the accumulation of calcium in apple (Malus × domestica Borkh. ‘Braeburn’) fruit

SummaryOrchards displaying calcium (Ca) deficiency are a common phenomenon worldwide, despite the presence of sufficient Ca in the soil and the plant. A 3-year trial was conducted between the 2007 – 2008 and 2009 – 2010 growing seasons to evaluate the contributions of soil and foliar Ca applications to Ca concentrations in ‘Braeburn’ apple (Malus × domestica Borkh.) fruit. Ca(NO3)2 (Calflo; Yara Africa, Fourways North, South Africa) was applied as six separate foliar sprays until run-off. Applications were made at 1-week intervals between approx. 21 – 70 d after full bloom (DAFB) at 6.75 ml l–1. Soil applications of Ca (TropicoteTM; International ASA, Oslo, Norway) at 300 kg ha–1 were applied at fruit set, or after harvest, according to standard practice. Mineral analysis was conducted to assess the soluble Ca concentrations of whole fruit (without pips and stalks), to quantify the contribution of foliar sprays or soil-applied Ca. Fruit Ca concentrations were maintained at satisfactory levels (4.5 mg Ca 100 g–1 FW) at harvest by applying a series of six foliar sprays early in the season (for all seasons) during the trial period. Fruit Ca concentrations at 80 DAFB were highest in the treatments with foliar applications of Ca. In 2009 – 2010, Ca concentrations in apple fruit were lowest (8.38 mg 100 g–1 FW) for soil application of Ca at fruit set. Ca applications to soil after harvest in the previous season, and soil applications shortly after fruit set in the current season, did not significantly increase Ca concentrations in current-season fruit, providing soil Ca levels were above the minimum requirement for apple trees. A possible explanation is that apple trees regulate their uptake of Ca through the roots when soil Ca is available in sufficient quantities. This confirms the importance of active root growth for efficient Ca uptake by apple trees when applying Ca to the soil.

Expression profiling of cell cycle genes reveals key facilitators of cell production during carpel development, fruit set, and fruit growth in apple (Malus×domestica Borkh.)

Cell production is an essential facilitator of fruit growth and development. Cell production during carpel/floral-tube growth, fruit set, and fruit growth, and its regulation by cell cycle genes were investigated in apple (Malus×domestica Borkh.). Cell production was inhibited during late carpel/floral-tube development, resulting in growth arrest before bloom. Fruit set re-activated cell production between 8 d and 11 d after full bloom (DAFB) and triggered fruit growth. The early phase of fruit growth involved rapid cell production followed by exit from cell proliferation at ∼24 DAFB. Seventy-one cell cycle genes were identified, and expression of 59 genes was investigated using quantitative RT-PCR. Changes in expression of 19 genes were consistently associated with transitions in cell production during carpel/floral-tube growth, fruit set, and fruit growth. Fourteen genes, including B-type cyclin-dependent kinases (CDKs) and A2-, B1-, and B2-type cyclins, were positively associated with cell production, suggesting that availability of G2/M phase regulators of the cell cycle is limiting for cell proliferation. Enhanced expression of five genes including that of the putative CDK inhibitors, MdKRP4 and MdKRP5, was associated with reduced cell production. Exit from cell proliferation at G0/G1 during fruit growth was facilitated by multiple mechanisms including down-regulation of putative regulators of G1/S and G2/M phase progression and up-regulation of KRP genes. Interestingly, two CDKA genes and several CDK-activating factors were up-regulated during this period, suggesting functions for these genes in mediating exit from cell proliferation at G0/G1. Together, the data indicate that cell cycle genes are important facilitators of cell production during apple fruit development.

Quantification and histochemical localization of ascorbic acid in ‘Delicious,’ ‘Golden Delicious,’ and ‘Fuji’ apple fruit during on-tree development and cold storage

Apple fruit are subject to multiple stressors during pre- and post-harvest development. Stress-induced reactive oxygen species (ROS) can be detrimental to the fruit, and ascorbic acid (AsA) is involved in many of the antioxidant pathways that detoxify ROS. An inclusive study to characterize AsA dynamics in ‘Delicious,’ ‘Golden Delicious,’ and ‘Fuji’ apples during pre- and post-harvest development was performed. AsA was quantified in fruit harvested prior to, at, and following attainment of physiological maturity. Fruit harvested at physiological maturity was stored in air at 0.5 °C and AsA was monitored at monthly intervals. AsA content in peel exceeded that in cortex for all cultivars at all sampling points. AsA in cortex declined early in fruit development and remained low relative to peel throughout development and storage. During development there was a slight increase in the quantity of AsA at physiological maturity, which correlates with an increase in internal ethylene. ‘Delicious’ apples harvested at 161 d after full bloom (DAFB) had the highest quantity of AsA, followed by ‘Golden Delicious’ at 149 DAFB and ‘Fuji’ at 178 DAFB. AsA localization in fruit sections stained with silver nitrate supported the analytical data obtained via HPLC and revealed AsA localizes to the core line and vascular bundles later in fruit development, and this pattern continues during cold storage.

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

SummaryThis 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.