Fruit Titratable Acidity Research Articles

Long-term response of tomato plants to changing nutrient concentration in the root environment—the role of proline as an indicator of sensory fruit quality

The aim of the trial was to investigate the time course of changes in content of proline and organic compounds affecting sensory quality of ripe red tomatoes after nutrient concentration had been changed. Tomato (Lycopersicon esculentum Mill. cv. Counter) plants were grown in nutrient solutions containing equal nutrient ratios at either low or high concentration (N1=standard solution; N2=5.5 times the standard concentration). Immediately after first harvest of ripe tomatoes, half of the plants of each treatment were transferred to nutrient solutions of higher (from N1 to N2) or lower (from N2 to N1) nutrient concentration. Proline content in leaves of plants transferred to higher or lower nutrient concentration adjusted to control levels (N2 and N1, respectively) within 2 weeks. Growing and ripe fruit reached the corresponding control levels within the same time or 1–5 weeks later. Similar time courses were observed for sugar concentration and titratable acidity in fruit. Apart from leaves, proline content of young growing fruit also increased with increasing radiation intensity at high nutrient concentration. However, in ripe fruit, proline content increased only with low to moderate radiation intensity and decreased when a certain stress level was exceeded. Similar results were found for osmolality and sugar concentration of ripe fruit, while titratable acidity remained rather unaffected by radiation. The role of proline as an indicator of sensory fruit quality is discussed.

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

SummaryTo 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.

Partial rootzone drying and deficit irrigation of ‘Fuji’ apples in a semi-arid climate

The effects of deficit irrigation (DI) and partial rootzone drying (PRD) on apple (Malus domestica Borkh. Cv. ‘Fuji’) yield, fruit size, and quality were evaluated from 2001 to 2003 in the semi-arid climate of Washington State. PRD and DI were applied from about 40 days after full bloom until just before (2001, 2002) or after (2003) harvest and compared to a control irrigation (CI). Irrigation was applied once a week using two micro-sprinklers per tree. Soil-water content in CI was maintained above 80% of field capacity using micro-sprinklers on both sides of a tree. The DI and PRD were irrigated at about 50% (2001–2002) and 60% (2003) of the CI, but differed in placement of irrigation. For DI both micro-sprinklers were operated whereas PRD was irrigated using only one micro-sprinkler wetting half the rootzone compared to CI and DI. Wetting/drying sides of PRD trees were alternated every 2–4 weeks (2001, 2002) or when soil-water content on the drying side had reached a threshold value (2003). Seasonal (1 May–31 October) potential evapotranspiration (ET0) was 967, 1002, and 1005 mm for 2001, 2002, and 2003, and rainfall totaled 58, 39, and 21 mm, respectively. Irrigation amounts applied were 596, 839, and 685 mm in the CI; 374, 763, and 575 mm in the DI; and 337, 684, and 513 mm in the PRD for the 2001, 2002, and 2003 seasons. Higher irrigation volumes in 2002 were due to excessive (177–324 mm) irrigations after harvest. No significant differences were found in yield and fruit size among treatments in 2001 and 2003. In 2002, DI had significantly lower yield than CI, while the yield of PRD did not differ from CI and DI. Fruit from DI and PRD were firmer and had higher concentrations of soluble solids than fruit from CI, both at harvest and following short-term storage at 20°C, but differences to CI were significant in 2002 only. Treatment effects on fruit titratable acidity were inconsistent. Additional water was preserved in the soil profile under PRD compared to DI in 2001 and 2003, but no statistical differences were found between PRD and DI in 2002. Approximately 45–50% of irrigation water was saved by implementing newly developed DI and PRD irrigation strategies without any significant impact on fruit yield and size with PRD. However, apple yield was reduced by DI compared to CI in the second year.

Response of Primocane-Fruiting ‘Polana’ Red Raspberry to Boron Fertilization

ABSTRACT The objective of this study was to examine the response of red raspberry to boron (B) fertilization. The experiment was carried out during 2002–2003 in a commercial plantation in central Poland on primocane-fruiting ‘Polana’ raspberries planted on a sandy loam soil with low status of organic matter and hot water-extractable B. Raspberries were fertilized with B via foliar or soil application. Foliar B sprays were made four times per season: two weeks before flowering, at the beginning of blooming, and three and six weeks later. In each spray treatment, B was used at a rate of 0.1 kg ha−1. Soil B was applied at the stage of bud break at a rate of 1 kg ha−1. Plants untreated with B served as a control. The results showed that B fertilization, regardless of application mode, increased flower and leaf B concentrations, fruit set, and berry yield. Fruit of B-fertilized plants were firmer, and had higher soluble solids concentrations and numbers of drupelets than those of the control plants. Boron fertilization had no effect on plant vigor, mean berry weight, and titratable acidity of fruit. The obtained results indicated that on coarse-textured soils with low B status, soil or foliar B application should be recommended in red raspberry cultivation to increase yield and improve berry quality.

Response of ‘Jonagold’ Apple Trees in the First Three Years after Planting to Mono-Ammonium Phosphate Fertilization Under Replant Problem Conditions

The objective of the experiment was to examine response of immature apple trees to application of mono-ammonium phosphate (MAP) fertilizer on replant problem soil. The study was carried out during 2001–2003 under a greenhouse on ‘Jonagold’ apple trees/M.9 EMLA planted singly in 50 L polyethylene containers filled with a sandy loam soil with low status of both organic matter and phosphorus (P) in soil solution. This soil originated from an apple orchard unfertilized with P for 23 years. The biological test showed the presence of specific replant disease in the soil. Immediately before apple tree planting, the soil was mixed with MAP at rates of 1, 2, and 3 g L− 1. Trees grown in the soil untreated with MAP served as a control. Each year apple trees were drip-irrigated and supplied with nitrogen (N) at differentiated rates to achieve a level of 50 g N per plant. The results showed that MAP application increased soil solution P status. Simultaneously, MAP supply at rates of 2 and 3 g L− 1 caused a drop in soil pH value in the last two years of the experiment. MAP treatments increased both dry weight and length of fine roots (< 2 mm in diameter), vigor of trees, the number of flower clusters per tree, flower intensity, the number of fruits per tree, and P concentrations in leaf and fruit tissues. Fruits from MAP-supplied trees were firmer than those of the control trees. Mean fruit weight, titratable acidity, and soluble solids concentration of ‘Jonagold’ apples at harvest were not influenced by MAP treatment. Fruits from MAP-supplied apple trees had increased calcium concentration only in one year. It is concluded that pre-plant application of MAP at a rate of 1g L− 1can be recommended on coarse-textured soils with low P status in soil solution to increase precocity of apple trees. However, MAP-supplied apple trees have to be watered to avoid the risk of osmotic stress.

THE QUALITY AND STORABILITY OF APPLES CV. ´JONAGORED´ SELECTED AT-HARVEST BY TIME-RESOLVED REFLECTANCE SPECTROSCOPY

Apple maturity at harvest is a critical factor which affects ripening and determines the post-harvest utilization of fruits. A new non-destructive technique, Time-Resolved Reflectance Spectroscopy (TRS), which measures separately the two optical properties of absorption and scattering at a deepness of 1-2 cm in the fruit flesh, has been successfully used for determining the maturity at harvest of nectarines in order to predict their softening rate and so to choose their marketing destinations. The aim of this work was to evaluate the usefulness of the absorption coefficient measured at 630 nm (μ a 630) by TRS to assess apple quality at harvest and after storage. 'Jonagored' apples were picked on 30 August and 13 September 2002. 150 fruits/pick were ranked by decreasing μ a 630 (from less to more mature) and divided into three maturity classes (less, medium and more mature). At-harvest, at the end of six months' storage at 1°C in normal or Controlled Atmosphere (1% O 2 , 2% CO 2 ) and after 7 days of shelf-life at 20°C, apples were analysed for fruit mass, skin colour, firmness, soluble solids (SS) and titratable acidity (TA). At the end of shelf-life, less and more mature fruits were assessed by sensory analyses and for juice content. The absorption coefficient μ a 630 was significantly higher in first harvest apples. Apples with higher μ a 630 had lower fruit mass, lower % blush both at harvest and after storage. Fruits classified as more mature by TRS had less TA at harvest and more SS after storage; at sensory analyses these fruits were significantly sweeter, more aromatic and pleasant. It can be concluded that TRS can be used to select apples according to maturity and so to separate fruits of different quality within the same batch.

EFFECT OF 1-MCP ON ´ABBÉ FÉTEL´ PEARS SORTED AT HARVEST BY TIME-RESOLVED REFLECTANCE SPECTROSCOPY

1-Methylcyclopropene (1-MCP) is an inhibitor of ethylene action, but its effectiveness and dose response in pears is variable from year to year and seems to be related to fruit maturity. In order to try to tune the 1-MCP dose at each maturity stage, 'Abbe Fetel' pears were picked on 1 September 2003, analysed by time-resolved reflectance spectroscopy (TRS), a new non destructive method for assessing fruit maturity, obtaining the absorption coefficient at 690 nm (μ a 690) for every fruit. Then pears were ranked by decreasing μ a 690 and divided into two maturity classes (less and more mature). Fruits in each class were randomised between the 1-MCP (0, 100 and 300 ppb) and storage (-0.5°C, NA or CA 2% O 2 + 0.7 % CO 2 ) treatments. 1-MCP was applied on the day after harvest at -0.5°C for 30 h. Analyses of fruit mass, colour, firmness, soluble solids (s.s.) and titratable acidity were carried out at harvest and, along with ethylene production rate, after 4 and 6 months' storage and during shelf life (7 days at 20°C). At harvest, μ a 690 was correlated to s.s., mass and titratable acidity, but not to firmness. After storage, the selection of fruit according to maturity affected fruit colour and the susceptibility to superficial scald, especially in control fruits stored in NA. In this experiment, on average, treated fruit were not able to soften below 40 N. So TRS measurement of μ a 690 on 'Abbe Fetel' pears could be used as maturity index at harvest for this cultivar; however, due to the strong effect of 1-MCP treatment, even at 100 ppb, the response of less and more mature fruit was not very different as regards firmness and ethylene production. More data are needed to check if there could be a relation between the maturity stage as assessed by TRS, and the optimum 1-MCP dose for both ripening and control of superficial scald.

INFLUENCE OF PREHARVEST CALCIUM TREATMENTS ON POSTHARVEST QUALITY OF SOME ESTONIAN APPLE CULTIVARS

Current research was conducted with apple (Malus domestica) cultivars Liivi Kuldrenett, Krameri tuvioun, Talvenauding and Tellissaare at Estonian Agricultural University during 2002-2003. The aim of the research was to find out the influence of preharvest calcium sprays from different sources, CaCl 2 and Ca (NO 3 ) 2 , on postharvest quality and storability of apples in normal atmosphere. Storage period for 'Liivi Kuldrenett' and 'Krameri tuvioun' was 4 months, for 'Talvenauding' 6 months and for 'Tellissaare' 7 months. Following variables were measured after harvest and monthly during storage: loss of marketable yield, content of fruit nitrogen and calcium, dry matter, soluble solids and titratable acids. Main physiological disorders such as bitter pit, physiological spot and superficial scald were scored visually every month. Average effect of calcium treatment on the amount of spoiled fruits at the end of the storage was not significant, but in most cases effect of cultivar was remarkable. Content of fruit soluble solids, titratable acids and dry matter after harvest was significantly reduced by calcium treatment and had values from 12.8 to 11.7% for soluble solids, from 0.79 to 0.67% for titratable acids and from 13.1 to 12.3% for dry matter in control and calcium-treated variants, respectively. Bitter pit incidence appeared mostly during first two months of storage and was significantly reduced by calcium treatment, but incidence of physiological spot in calcium-treated 'Krameri tuvioun' was increased. Preharvest fertilization with CaCl 2 and Ca(NO 3 ) 2 significantly increased both calcium and nitrogen content in apple fruits. Correlations between quality characteristics after harvest and incidence of physiological disorders are presented and discussed.

Response of Black Currant to Boron Fertilization

ABSTRACT The objective of this study was to examine the reproductive and vegetative response of black currant to soil and foliar applications of boron (B). The experiment was carried out during the 2001 and 2002 seasons in a commercial plantation in central Poland on mature ‘Ojebyn’ black currant planted on a sandy loam soil with low status of hot-water-soluble B. Black currant bushes were foliar or soil supplied with B (as boric acid). Foliar B sprays were made on the same bushes 3 times per season (2 weeks before flowering, at the beginning of blooming, and at petal fall) at a rate of 0.2 kg ha−1 in each spray treatment. Soil B was applied at a rate of 2 kg ha−1 at the bud break stage. Bushes untreated with B served as the control. The results showed that vigor of black currant bushes, weight of 100 berries, and soluble solids concentration and titratable acidity of fruit were unaffected by B fertilization. Foliar B sprays increased B concentrations in flowers and leaves, and also enhanced the fruit set and as well as cropping of black currants. Soil B application enhanced leaf B status but had no effect on flower B level and plant yield. These results indicate that foliar B sprays applied at or around the time of flowering should be recommended for black currant plantations to increase productivity of plants containing an insufficient flower B level.

Effects of Ammonium to Nitrate Ratio and Salinity on Yield and Fruit Quality of Large and Small Tomato Fruit Hybrids

Tomato cultivars respond differently to nitrogen (N) sources and to saline conditions, in terms of both yield and fruit quality. Interactions between salinity and ratios with tomato genotypes were studied. The effect of four ammonium levels (0, 1, 2, 4 mM of total 8 mM N) and two salinity levels (0 and 45 mM NaCl) on cv. “R-144”, and the effect of two salinity levels (0 and 45 mM NaCl) on four tomato hybrids (“R-144”, “R-175”, “FA612”, and “FA624”) were studied in two greenhouse experiments. The effects of two levels, (0 and 2 mM out of total N at 8 mM), and two salinity levels (0 and 20 mM NaCl) on large-fruit (“R-144”) and small-fruit (“FA612”) tomato hybrids were also studied in a net-house. The NaCl at 45 mM resulted in a smaller leaf area index (LAI), lower plant dry matter and lower fruit yield than controls. Addition of 1 mM to the nutrient solution contributed to improved growth. Genotypes bearing large fruits were more prone to suffer yield losses under saline conditions than those with small fruits. In the second experiment, salinity treatment resulted in improved fruit TSS, EC and titratable acidity in all of the hybrids except of “FA612”. Fruit TSS was inversely correlated with yield. However, the ratio in TSS decline versus yield varied among the hybrids. At mild salinity (20 mM NaCl), fruit TSS and titratable acidity were significantly increased in “R-144” while yield was slightly decreased. Transpiration rate decreased with the presence of ammonium in the nutrient solution in both hybrids. The highest and lowest values were obtained for “FA612” and “R-144”, respectively. The detrimental effect of salinity is mainly attributed to the decrease in LAI and the subsequent reduction in water uptake, resulting in low fruit weight. Addition of 1 mM ammonium to 7 mM nitrate in the nutrient solution had an ameliorating effect on tomato fruit yield under salinity.

Effects of irrigation amount on water relations, vegetative growth, yield and fruit composition of Sauvignon blanc grapevines under partial rootzone drying and conventional irrigation in the San Joaquin Valley of California, USA

SummaryA study was conducted to investigate the effect of partial rootzone drying (PRD) in comparison to conventional irrigation (CI) at both 0.8 and 0.4 crop evapotranspiration (ETc) on water relations, vegetative growth, yield, and fruit composition of mature Sauvignon blanc grapevines (Vitis vinifera L.) in the San Joaquin Valley of California, USA. Soil moisture decreased quickly on the dry side and was restored quickly on the wet side of PRD-treated vines after switching. There was no yield reduction while vegetative growth was reduced at 0.4 ETc. However, in contrast to published studies assuming and emphasizing the role of PRD, this study demonstrated that only an irrigation amount of 0.4 ETc reduced stomatal conductance, transpiration, pruning weight, number of lateral shoots, number of active growing points, and fruit titratable acidity (TA). It appears that the irrigation amount, not PRD, is the determining factor inducing water stress and reducing transpiration and vegetative growth. With vine water relations only occasionally affected and no improvement in vine performance and vine water use at the same irrigation amount, PRD is not recommended for winegrape production with Sauvignon blanc under similar climatic conditions and cultural practices as in this study. Commercial implementation of PRD as described in previous studies should not be recommended until PRD is proven advantageous over CI at the same irrigation amount.

Response of Apple to Fertigation of N and K under Conditions Susceptible to the Development of K Deficiency

A split-plot experimental design was imposed in the year of planting and maintained for the first five growing seasons in a high density apple orchard on M.9 rootstock planted at 1.5 m (within row) × 4 m (between row) in a loamy sand soil susceptible to K deficiency when drip-irrigated. Four N-K fertigation treatments involving low (N1) and high (N2) rates of N combined with 0 (K0) or 15 g K/tree per year (K1) were applied in five replicated and randomized main plot units. Subplots consisted of three-tree plots of each of the apple cultivars Gala, Fuji, Fiesta and Spartan. Soil solution monitoring indicated the maintenance of distinctly different soil solution N and K concentrations in the respective N-K treatments during the study. The most important plant response was prevention of the development of K deficiency by the K1-fertigation treatment. Fertigation of 15 g K/tree generally increased leaf K, fruit K and Mg concentrations, fruit size and yield and fruit titratable acidity and red coloration at harvest for all cultivars. K fertigation also decreased leaf Mg and B concentrations, fruit N, P and Ca concentration and fruit firmness. In addition to leaf K concentrations &lt;1%, K deficiency was associated with fruit K concentrations &lt;100 mg/100 g fresh weight and soil solution K concentration &lt;5 mg·L-1. Increasing the rate of fertigated N when growth was constrained by K deficiency increased leaf N and Mn and decreased leaf P and B, but had no effect on tree vigor or fruit production and quality.

Effect of AMF inoculum from field isolates on the yield of green pepper, parsley, carrot, and tomato

Inoculum of an indigenous mixture of arbuscular mycorrhizal fungi (AMF) containingGlomus mosseae, Glomus fasciculatum, Glomus etunicatum, Glomus intraradices andScutellospora sp. was applied to four of the most frequently used crop species in Slovenia: green pepper (Capsicum annuum), parsley (Petroselinum crispum), carrot (Daucus carrota) and tomato (Lycopersicon esculentum). A simple, feasible, and effective protocol for application of AMF biotechnology in horticulture was adopted. Mycorrhizal inoculation significantly increased the plant biomass parameters of pepper, and parsley and the root biomass of carrots. Statistically significant correlations between biomass parameters of pepper, parsley, and the root biomass of carrots with mycorrhizal colonization parameters (mycorrhizal frequency (F%), global mycorrhizal intensity (M%) and arbuscular richness (A%) were calculated. A significant increase in chlorophyll content was observed in mycorrhizal parsley and a significant increase in carotenoids was observed in mycorrhizal parsley, carrots, and tomato fruits. A significant increase in titratable acidity of fruits from inoculated tomato plants indicates prolonged fruiting period of mycorrhizal tomatoes. In addition, inoculation with an indigenous AMF mixture significantly increased the mycorrhizal potential of soil and thus the growth of non-inoculated plants in the second season. Thus, the results confirmed the potential of applying mycorrhizal biotechnology in sustainable horticulture.

Effect of Calcium and Boron Sprays on Yield and Quality of “Elsanta” Strawberry

The aim of the experiment was to examine the effects of foliar applications of calcium (Ca) and boron (B) on yield and fruit quality of “Elsanta” strawberries grown on a sandy loam soil with low status of available B. The study was conducted in 1999–2000 at a commercial strawberry plantation in Central Poland. Cold‐stored strawberries were planted in 1998 at a spacing of 0.25 × 0.8 m. The following treatments were applied: (i) five sprays of Ca as CaCl2 at a rate of 1.5 kg Ca ha−1 spray−1 with addition of Tween 20 adjuvant at 0.1%; the first spray was performed at the petal fall stage and the next at 5‐day intervals; (ii) three sprays of B as Borvit material at a rate of 160 g B ha−1 spray−1 at the beginning of flowering and 5, and 10 days later; (iii) sprays of B and Ca as in the combination of (i) and (ii). Plants sprayed with water served as the control. Results showed that fruit and leaves from Ca‐treated plants had increased Ca concentrations. Sprays with B increased status of this microelement in fruit and leaf tissues. Treatments did not affect total and marketable fruit yield, mean berry weight, the number deformed fruit, soluble solids concentration and titratable acidity of fruit at harvest. Fruit sprayed with Ca or B plus Ca were firmer and more resistant to Botrytis rot at harvest and after 3 days of holding at 18°C compared to those of control plots. Moreover, sprays of Ca or B plus Ca increased soluble solids concentration and titratable acidity of fruit after 3 days of holding at room temperature. These results indicate that sprays of CaCl2 with addition of Tween 20 should be recommended to improve quality and shelf‐life of strawberry fruit, particularly in proecological production where application of fungicides is restricted.

HARVEST MATURITY RELATIONSHIP TO FLAVOR REGENERATION AFTER CA-STORAGE OF 'DELICIOUS' APPLES

Red Delicious producers in the USA are under increasing pressure to produce fruit with optimum “on-shelf” dessert quality following storage. In addition to traditional quality measures like firmness and soluble solids, we are studying the ripening-related events that affect flavor perception. Ester production is always closely linked to the onset of climacteric ripening, while prolonged low-oxygen storage is usually detrimental to volatile production. Experiments focused on optimum harvest time for maintaining sweetness, sourness and aroma generating capacity during CA storage. In multiple-harvest experiments with ‘Redchief Delicious’ apples, we investigated the relationship between the internal ethylene maturity indicator and flavor retention and regeneration after storage for different lengths of time. Using a cohort of untrained panelists, it was found that overall flavor perception and perceived fruit ripeness begins to increase at the onset of the climacteric. CA conditions reduce post-storage volatile production when compared to those stored in refrigerated air although not to a level below those displayed in “over-mature” fruit at harvest after 3 months in storage. As harvest maturity advanced, the time required to regenerate aroma volatiles to an “optimum” level after removal from CA storage decreased markedly. Apparently, there is a linear relationship between attainment of optimal eating quality and time out of storage. Firmness, soluble solids, and titratable acidity of fruit from all harvest dates remained at acceptable levels throughout the post-storage ripening period.

Thresholds of Leaf Nitrogen for Optimum Fruit Production and Quality in Grapefruit

Fertilization is critical for sustainable production of citrus on sandy soils. However, information on nutritional diagnosis standards for grapefruit (Citrus × paradisi Macfad. ) is lacking and this information is needed for implementation of best management practices (BMPs). A field experiment was conducted from 1997 to 2000 on a Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf) with 30‐yr‐old+ white Marsh grapefruit trees on sour orange (Citrus aurantium L.) rootstock to evaluate irrigation and fertilization effects on fruit yield and quality and to validate leaf nutrient concentration standards for guiding fertilization of grapefruit. Fertilizers were applied as water soluble granular (WSG, 3 applications yr−1), by fertigation (FRT, 15 applications yr−1), or as controlled‐release fertilizers (CRF, 1 application yr−1) and at five rates (0, 56, 112, 168, or 224 kg N ha−1 yr−1) with an N:P:K blend (1.0:0.17:1.02). Fruit yield and quality were not affected by irrigation treatments or fertilizer sources. There was a significantly positive correlation between leaf N concentrations and N rates (r = 0.98**). Fruit yield was linearly related to N rates or leaf N concentrations. At 90% of maximum yield, leaf N concentrations (dry weight basis) were 22 to 23 g kg−1 Fruit quality parameters such as soluble solid concentration (SSC), juice, and total soluble solids (TSS) were positively correlated with leaf N concentrations, whereas fruit titratable acidity (TA) was negatively related to leaf N concentrations or N rates. The effect of N rate on TA outweighed that on SSC and consequently, the SSC/TA ratio decreased with increasing N rates or leaf N concentration. Fruit size was quadratically related to N rate or leaf N concentration. Overall, fruit sizes and SSC/TA ratios were acceptable for fresh marketing or processing at leaf N concentrations of 22 to 23 g kg−1 Therefore, this leaf N concentration of 22 to 23 g kg−1 can be considered the optimal concentration guideline for fertilization of grapefruit provided that other nutrients are sufficient.

Effects of boron fertilization on `Conference' pear tree vigor, nutrition, and fruit yield and storability

The aim of the study was to examine the response of pear (Pyrus communis L.) trees to soil and foliar applications of boron (B). The experiment was carried out during 2000–2001 in a commercial orchard in Central Poland on mature `Conference' pear trees grafted on Pyrus communis var. caucasica seedlings planted at a spacing of 4 × 2.5 m on a sandy loam soil with a low hot water-extractable B status. Annually, foliar sprays with B were applied. (i) before full bloom (at green and white bud stage, and when 1–5% of flowers was at full bloom), (ii) after flowering (at petal fall, and 7 and 14 days after the end of flowering), or (iii) postharvest in fall (approximately 6 weeks before leaf fall). Spray treatments involved application of B at a rate of 0.2 kg ha−1 in spring or 0.8 kg ha−1 in fall. Additionally, other trees were supplied with soil-applied B at the bud break stage at a rate of 2 kg ha−1. Trees untreated with B served as the control. The results revealed that foliar applications of B before full bloom or after harvest increased fruit set and fruit yield. Tree vigor, mean fruit weight, firmness, soluble solids concentration and titratable acidity of fruits at harvest were not affected by B treatments. Foliar B sprays before full bloom or after harvest increased B concentrations in flowers, and both leaves and fruitlets at 40 days after flowering. Only the foliar treatments after flowering and soil fertilization with B increased the content of this microelement in fruit and leaves at 80 and 120 days after full bloom. Foliar B application before full bloom or after harvest increased calcium (Ca) in fruitlets at 40 days after full bloom, in fruit, and in leaves at 80 and 120 days after full bloom. Nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) in plant tissues were not affected by B fertilization. After storage, and also after the ripening period, fruits from the trees sprayed with B before full bloom or after harvest had higher firmness and titratable acidity than those from the control trees. After the ripening period, fruits from the trees sprayed with B before full bloom or after harvest had lower membrane permeability and were less sensitive to internal browning than the control fruits. These findings indicate that prebloom and postharvest B sprays are successful in increasing pear tree yielding and in improving fruit storability under the conditions of low B availability in the soil.

Thresholds of Leaf Nitrogen for Optimum Fruit Production and Quality in Grapefruit

Fertilization is critical for sustainable production of citrus on sandy soils. However, information on nutritional diagnosis standards for grapefruit (Citrus × paradisi Macfad. ) is lacking and this information is needed for implementation of best management practices (BMPs). A field experiment was conducted from 1997 to 2000 on a Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf) with 30-yr-old+ white Marsh grapefruit trees on sour orange (Citrus aurantium L.) rootstock to evaluate irrigation and fertilization effects on fruit yield and quality and to validate leaf nutrient concentration standards for guiding fertilization of grapefruit. Fertilizers were applied as water soluble granular (WSG, 3 applications yr−1), by fertigation (FRT, 15 applications yr−1), or as controlled-release fertilizers (CRF, 1 application yr−1) and at five rates (0, 56, 112, 168, or 224 kg N ha−1 yr−1) with an N:P:K blend (1.0:0.17:1.02). Fruit yield and quality were not affected by irrigation treatments or fertilizer sources. There was a significantly positive correlation between leaf N concentrations and N rates (r = 0.98**). Fruit yield was linearly related to N rates or leaf N concentrations. At 90% of maximum yield, leaf N concentrations (dry weight basis) were 22 to 23 g kg−1 Fruit quality parameters such as soluble solid concentration (SSC), juice, and total soluble solids (TSS) were positively correlated with leaf N concentrations, whereas fruit titratable acidity (TA) was negatively related to leaf N concentrations or N rates. The effect of N rate on TA outweighed that on SSC and consequently, the SSC/TA ratio decreased with increasing N rates or leaf N concentration. Fruit size was quadratically related to N rate or leaf N concentration. Overall, fruit sizes and SSC/TA ratios were acceptable for fresh marketing or processing at leaf N concentrations of 22 to 23 g kg−1 Therefore, this leaf N concentration of 22 to 23 g kg−1 can be considered the optimal concentration guideline for fertilization of grapefruit provided that other nutrients are sufficient.

Effects of different P-sources in soil on increasing growth and mineral uptake of mycorrhizal &lt;em&gt;Vitis vinifera&lt;/em&gt; L. (cv Victoria) vines

&lt;p style="text-align: justify;"&gt;The effect of different P-sources on growth, leaf chemical composition, and fruit soluble solids and acid content was evaluated in mycorrhizal Victoria grapevine variety gralted onto the rootstocks 3309C or 11 OR. Mycorrhizal and non mycorrhizal plants were grown in 20 L pots containing 20 kg soil supplemented with different P-forms: (Calcium bis-dihydrogen-phosphate, tri-calcium phosphate, aluminium phosphate, iron (III) phosphate) with different solubility, equivalent to 90 kg P.ha&lt;sup&gt;-1&lt;/sup&gt;. The percent of mycorrhizal root colonization was higher in insoluble P-form treatments compared to control or to soluble P-form treatment (CaDP), ranging from 66 to 84 % in treatments receiving insoluble P, from 36.67 to 38.33 % in control and from 25.33 to 27.33 % in soluble P-form treatments. The roots of 110R rootstock showed higher colonization rate compared to the 3309C. Mycorrhizal colonization increased both the pruning weight and number of nodes of the vines, up to 9 and 1.9 times respectively, according to the rootstock- P form combination. Mycorrhizal vines showed increased leaf concentrations in N, P, K, Ca. Fruit total soluble solids of mycorrhizal vines were about 30 % lower compared with those of the non mycorrhizal vines. Both factors, mycorrhizal colonization and P-forms had no significant effect in fruit titratable acidity.&lt;/p&gt;

Relationship of harvest maturity to flavor regeneration after CA storage of ‘Delicious’ apples

Red Delicious producers in the USA face increased pressure to produce fruit with optimum ‘on-shelf’ dessert quality following storage. In addition to firmness and soluble solids measurement other ripening-related events affect flavor perception. Ester production is always closely linked to the onset of climacteric ripening, while prolonged low-oxygen storage is usually detrimental to volatile production. Experiments focused on timing of the optimum harvest for maintaining sweetness, sourness and aroma generating capacity during CA storage. In multiple-harvest experiments with ‘Redchief Delicious’ apples, we investigated the relationship between the internal ethylene maturity indicator and flavor retention and regeneration after storage for different lengths of time. Using a cohort of untrained panelists, it was found that overall flavor perception and perceived fruit ripeness begins to increase at the onset of the climacteric. CA conditions reduce post-storage volatile production when compared with those stored in refrigerated air although not to a level below those displayed in ‘over-mature’ fruit at harvest after 3 months in storage. As harvest maturity advanced, the time required to regenerate aroma volatiles to an ‘optimum’ level after removal from CA storage decreased markedly. A linear relationship between attainment of optimal eating quality and time out of storage was established. Firmness, soluble solids, and titratable acidity of fruit from all harvest dates remained at acceptable levels throughout the post-storage ripening period.