Tree age canopy position affect rind quality, fruit quality and rind nutrient contents

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Scientia Horticulturae 135 (2012) 137–144

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Tree age and canopy position affect rind quality, fruit quality and rind nutrientcontent of ‘Kinnow’ mandarin (Citrus nobilis Lour × Citrus deliciosa Tenora)

Samina Khalida,∗, Aman Ullah Malika, Basharat Ali Saleemb, Ahmad Sattar Khana,Muhammad Shafique Khalida, Muhammad Amina

a Postharvest Research and Training Centre, Institute of Horticultural Sciences, University of Agriculture, Faisalabad 38040, Pakistanb Punjab Agriculture (Extension) Department, Fruit and Vegetable Development Project, Sargodha, Pakistan

a r t i c l e i n f o

Article history:Received 6 July 2011Received in revised form 3 December 2011Accepted 8 December 2011

Keywords:‘Kinnow’ mandarinTree ageRind qualityMacronutrientsMicronutrients

a b s t r a c t

Rind quality is a critical factor affecting the external appearance and marketability of citrus fruit, especiallyfor fresh consumption. Among many factors affecting citrus rind quality, tree age is the most important,but remained unexplored. This study aimed to explore the effects of tree age on rind and fruit quality of‘Kinnow’ mandarin, the most important mandarin cultivar in Pakistan. For this purpose ‘Kinnow’ man-darin trees of different age (3, 6, 18 and 35 years), growing in a commercial orchard in the main citrusgrowing district, Sargodha, (latitude 32◦03′N and longitude 72◦40′E), were used. Fruit were harvestedat commercial maturity from internal and external canopy positions and assessed for various physico-chemical characteristics as well as rind macro- and micro-nutrients. Rind thickness (2.5 mm), percentageof rind mass (24.8%) and rag mass (24.1%), ascorbic acid (AA) (32 mg/100 mL), pH (3.07), non reducingsugars (5.85%), rind manganese (Mn) (0.125 ppm) and iron (Fe) (1.27 ppm) contents were higher in young3-year-old trees, whereas total sugars (7.6%), reducing sugars (2.2%), acidity (0.9%) and total soluble solids(TSS) (10.4 ◦Brix) were higher in 18-year-old trees. A correlation matrix was developed for nutrient con-tent and rind quality parameters. Rind thickness correlated negatively with rind P (r = 0.75), Ca (r = 0.79),Cu (r = 0.92), Mn (r = 0.74), Fe (r = 0.85) and Zn (r = 0.80) contents in 3-year-old trees, and with K (r = 0.73)content in 6-year-old trees, whereas 18- and 35-year-old trees exhibited no correlation between rindnutrient contents and rind thickness. For internal fruit quality, K correlated positively with rag mass (%)and TSS in 3-year-old trees, and was negatively correlated with rind mass (%) and TSS in 6-year-old treesand acidity in 35-year-old trees. This study highlights the role of potential nutrients which can help toimprove rind and fruit quality in young ‘Kinnow’ mandarin orchards in the future.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

‘Kinnow’ mandarin (Citrus nobilis Lour × Citrus deliciosa Tenora)has gained importance among citrus cultivars and has monopo-lized the citrus industry of Pakistan due to its good yield, freshconsumption and better adaptation to the agro-environmental con-ditions of Punjab (Ahmed, 2005). Pakistan ranks 11th in mandarinproduction (FAO, 2009), and ‘Kinnow’ mandarin shares more than60% in the country’s citriculture (Altaf and Khan, 2009). It is theleading exportable fruit commodity of Pakistan to Russia, Iran andthe Gulf States, and is an important source of foreign exchange.

Abbreviations: ECP, external canopy position; ICP, internal canopy position; TA,titratable acidity; AA, ascorbic acid; TSS, total soluble solids.

∗ Corresponding author. Tel.: +92 333 8046404; fax: +92 41 2409303.E-mail addresses: samina [email protected], [email protected]

(S. Khalid).

Pakistan exported 250,000 tons of ‘Kinnow’ mandarin during 2009(Anonymous, 2010).

Citrus fruit quality may be indicated by external features, suchas rind colour, size, and rind texture, and physical and biochemicalcharacters of its internal features, like seediness, juice and vitaminC contents, TSS, TA and TSS:TA ratio (Ahmed, 2005). Fruit qualityis influenced by various factors including cultural practices, suchas pruning, irrigation, fertilizer application and plant protectionmeasures (Mahmood and Sheikh, 2006). It is generally observedthat young ‘Kinnow’ mandarin trees produce fruit with coarserind and low juice content, and exporters are reluctant to acceptfruit from young orchards (Malik, 2006, personal communica-tion).

Tree age plays an important role in fruit quality, but studies todetermine its effect are rare in fruit crops and especially in citrus.Tree age affected acidity and TSS content of ‘Satsuma’ mandarin(Matsumato et al., 1972) and juice content, TSS, acidity and ripenessindex of oranges (Frometa and Echazabal, 1988). Ozeker (2000)reported that 20-year-old trees of ‘Marsh’ seedless grapefruit

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138 S. Khalid et al. / Scientia Horticulturae 135 (2012) 137–144

produced bigger fruit with thinner rinds compared with 34-year-old trees. Pome fruit harvested from young trees werehighly susceptible to postharvest disorders (Bramlage, 1993)and lower quality apples were obtained from trees of oldage (Smith, 2003). No studies have been published on therelationship between tree age and fruit quality of ‘Kinnow’mandarin.

Apart from tree age, fruit position in the canopy (Barry et al.,2003; 2004; Khan et al., 2009) and fruit size (Ketsa, 1990; Barryet al., 2004) also affect fruit quality. Jawanda et al. (1973) reportedthat fruit juice percentage, acidity and TSS were higher, and fruitsize and rind percentage were lower in the upper sides of citrustrees. Orange fruit harvested from upper canopy positions had highcontents of reducing sugars (Uchida et al., 1985), while no effect offruit position in the canopy was observed on total sugar content in‘Satsuma’ mandarin (Datio and Tominaga, 1981). Citrus fruit har-vested from the southern top canopy position had higher TSS andjuice contents than fruit from other canopy positions (Izumi et al.,1990). ‘Tarocco’ orange harvested from the external southern sideof the tree had higher TSS and lower acid levels, resulting in higherTSS:acid ratio and improved taste (Agabbio et al., 1999). Fruit mass,total juice per fruit, rind fresh and dry mass, and rind thicknessof fruit from internal canopies of ‘Kinnow’ mandarin, ‘Red blush’grapefruit, ‘Valencia’ orange and ‘Lisbon’ lemon were significantlyhigher compared with fruit from external canopy positions (Fallahiand Moon, 1989).

Many researchers have determined the nutrient acquisition indifferent parts of citrus fruit (Raza et al., 1999; Paramasivam et al.,2000; Mattos et al., 2003; Xiao et al., 2007). Some reports are avail-able on fruit nutrient contents in relation to tree age in ‘Navel’orange (Storey and Treeby, 2000, 2002), avocado (Snijder et al.,2002) and guava (Asrey et al., 2007), and correlation matrixes wereestablished between fruit nutrient contents and fruit quality in cit-rus (Morgan et al., 2005) and apple (Casero et al., 2005; Tahir et al.,2007). However, no study has been reported to determine rindnutrient contents from trees of varying age and to establish a cor-relation between rind nutrient contents and rind quality. There isa need for comprehensive research to determine the possible rea-sons for variation in fruit quality with tree age and fruit position onthe tree.

The present study aimed to determine (1) the effect of treeage and canopy position on fruit quality, and (2) the correlationbetween rind nutrient contents and rind quality, in ‘Kinnow’ man-darin.

2. Materials and methods

2.1. Plant material

‘Kinnow’ mandarin fruit is harvested from a commercial citrusorchard in the main ‘Kinnow’ mandarin growing district, Sargodha(latitude 32◦03′N and longitude 72◦40′E), Punjab, Pakistan. Theexperimental trees were grafted on rough lemon (Citrus jambhiriLush.) rootstock planted at 6 m× 6 m, with commercial agronomicpractices in the area.

Four age groups of trees were selected, viz. 3-, 6-, 18- and35-year-old trees. Eight uniform and healthy trees per age groupwere tagged. Fruit were randomly harvested at maturity with handclippers mostly at shoulder height from individual selected trees,both from the external and internal canopy positions (in 3-year-old trees only from the external canopy as these trees had a smallcanopy volume). Immediately after harvest, fruit were brought tothe Postharvest Research and Training Centre, Institute of Horti-cultural Sciences, University of Agriculture, Faisalabad, Pakistan.Fruit harvested from trees of the same age group and same canopy

position was pooled, washed with tap water and air dried. Ten fruitwere taken as a treatment unit, replicated four times (n = 40). Thesefruit were used for the determination of external and internal phys-ical characteristics, rind nutrient contents and biochemical analysisof the juice.

2.2. External fruit quality

Different rating categories were used for the estimation ofrind smoothness (1 = very rough, 2 = rough, 3 = slightly smooth,4 = smooth and 5 = very smooth), and rind colour (1 = 100% green,2 = 75% green; 25% orange, 3 = 50% green; 50% orange, 4 = 25% green;75% orange and 5 = 100% orange).

2.3. Internal fruit quality

Internal fruit quality parameters, including rind, rag juice andseed, were weighed separately, and their quantities were expressedin percentage (Saleem et al., 2008).

2.4. Biochemical analysis

Fruit juice pH was measured with a digital pH meter (HI 98107,Hanna, Mauritius) at 18 ± 2 ◦C and TSS (◦Brix) was determinedwith a digital referactometer (Atago, ATC-1, Tokyo, Japan). TA(%), ascorbic acid (AA) (mg/100 mL), reducing, non-reducing andtotal sugars (%) were determined by using standard techniques inthe laboratory as adopted by Malik et al. (2003) and Khan et al.(2009). Juice samples were titrated against 0.1 N NaOH using 2–3drops of phenolphthalein as an indicator, and the results wereexpressed in percentage. Five mL of aliquot (containing 10 mL ofjuice and 90 mL of 0.4% oxalic acid solution) was titrated against2,6-dichlorophenolindophenol dye solution for the determinationof AA. Reducing sugars were titrated against Fehling’s A and B solu-tions using methylene blue as an indicator, to brick-red end-point.For total sugars, juice samples were first acid hydrolyzed and thentitrated by the method described for reducing sugars.

2.5. Rind mineral analysis

Rind from fruit of the different age groups was sliced, air-driedat room temperature for 1–2 d and then oven dried at 70 ◦C, groundby electric grinder and stored in labeled plastic containers at roomtemperature. One gram of sample was digested for nitrogen deter-mination and the other amount was wet-digested for phosphorous,potassium, calcium, zinc, copper, iron and manganese determina-tion using the method described by Chapman and Parker (1961).

2.6. Statistical analysis

A two-factor factorial Completely Randomized Design (CRD)was used for analysis of the data using M-Stat C software, and treat-ment means were compared with Duncan’s New Multiple RangeTest (Freed, 1994).

3. Results

3.1. External fruit quality

External fruit quality parameters were significantly affectedby tree age (Fig. 1). Rind smoothness scores (3.4) were high infruit harvested from 35-year-old trees, whereas the lowest rindsmoothness scores (2.5) were recorded in fruit of 3-year-old trees.Rind colour scores were highest (3.9) for fruit from external treecanopy, whereas rind smoothness scores were higher (3.1) for fruitfrom internal canopy positions. Among tree age group, maximum


S. Khalid et al. / Scientia Horticulturae 135 (2012) 137–144 139

Fig. 1. Effect of tree age and canopy position on external quality parameters of‘Kinnow’ mandarin (n = 10).

rind smoothness scores (3.6) were measured from fruit of internalcanopy of 35-year-old trees. Rind colour scores (4.0) were highestfor fruit from the external canopy of 6-year-old trees.

3.2. Internal fruit quality

Juice mass (%) was highest (58.1) in fruit from 35-year-old treesand lowest (51.7) in fruit of 3-year-old trees (Fig. 2). Rind thickness(2.59 mm), rind mass (24.8%) and rag mass (24.1%) were highestin fruit of 3-year-old trees. Seed mass (1.6%) was highest in fruitof 6-year-old trees. Fruit from the external canopy position hadmarkedly higher rind mass (22.6%) and rind thickness (2.46 mm),whereas seed mass (1.37%) was higher for fruit from the internaltree canopy. Fruit harvested from the internal canopy of 35-year-old trees (oldest trees) had the highest juice mass (59.4%), whereasthe lowest juice mass (51.7%) was measured in fruit of 3-year-old trees. Fruit from the internal canopy of 6-year-old trees hadthe highest seed mass (1.88%), whereas the minimum seed mass(0.47%) was measured in 3-year-old trees.

3.3. Biochemical analysis

Fruit from 18-year-old trees had the highest TSS (10.4 ◦Brix), TA(0.92%), reducing sugars (2.24%) and total sugars (7.63%), whereasthe highest contents of AA (32 mg/100 mL), pH (3.07) and nonreducing sugars (5.85%) were determined in fruit from 3-year-oldtrees (Tables 1 and 2). In all trees from different age groups, fruitharvested from the external canopy surpassed the fruit harvestedfrom the internal canopy in terms of TSS (10.7 ◦Brix), reducing sug-ars (2.23%), non reducing sugars (5.73%) and total sugars (7.86%).Fruit from the internal canopy of the tree had the highest pH (2.94).Fruit from the external canopy of 18-year-old trees had the bestinternal fruit quality with maximum TSS (11.2 ◦Brix), TA (0.99%),reducing sugars (2.59%) and total sugars (8.21%), whereas fruit

from the external canopy of 3-year-old trees had TSS:TA (13.5),AA (32 mg/100 mL), pH (3.07) and non reducing sugars (5.85%).

3.4. Rind macronutrient contents

Rind macronutrient contents (N and P) were significantly higherin 18-year-old trees, K was higher in 6-year-old trees and Ca in 35-year-old trees. Fruit canopy position also had significant effect onrind macronutrient contents (Fig. 3); P and K were higher in internaltree canopy positions, whereas N was higher in the external canopy.The interaction of tree age and canopy position showed that N wasmaximum in the rind of fruit from the external canopy, whereasP was maximum in fruit from the internal canopy of 18-year-oldtrees. K was higher in the rinds of fruit from the internal canopy of6-year-old trees.

3.5. Rind micronutrient contents

Rind micronutrient analysis (Fig. 4) revealed that manganese(Mn) and iron (Fe) contents were statistically higher (12.5 ppmand 127.3 ppm, respectively) in fruit of younger plants (3-year-oldtrees) and lower (7.5 ppm and 95 ppm, respectively) in 18-year-old trees, whereas zinc (Zn) and copper (Cu) contents were notsignificantly affected by tree age. Manganese (Mn) was signifi-cantly higher in the internal canopy (10.1 ppm), whereas the othermicronutrients (Zn, Fe and Cu) were not significantly different.

3.6. Correlation between rind nutrient contents and rind quality

The correlation between rind quality and macro- and micro-nutrient contents relative to tree age showed that in 3-year-oldtrees, P (r = 0.75), Ca (r = 0.79), Cu (r = 0.92), Mn (r = 0.74), Fe (r = 0.85)and Zn (r = 0.80), and in 6-year-old trees, K (r = 0.73), correlatednegatively with rind thickness, while rind smoothness was neg-atively correlated with N (r = 0.74) in 18-year-old trees (Table 3).Irrespective of tree age, rind thickness correlated negatively withcalcium (Ca), whereas rind smoothness correlated positively withnitrogen (N) and phosphorous (P) and negatively with manganese(Mn) contents in rind.

3.7. Correlation between rind nutrient contents and internal fruitquality

In 3-year-old trees, rag content correlated negatively with N(r = 0.96) and positively with K (r = 0.99), and K correlated nega-tively with juice content (r = 0.80) and positively with TSS (r = 0.78)(Table 4). In 6-year-old trees, P (r = 0.74) and K (r = 0.81) correlatednegatively with rind whereas TSS (r = 0.92) correlated negativelywith K. In 35-year-old trees, TSS correlated negatively with N(r = 0.74), and acidity correlated with K (r = 0.78). Regardless of treeage, rind content correlated negatively with N (r = 0.38) and posi-tively with acid content (r = 0.44). P correlated positively (r = 0.65)with juice content and negatively with TSS (r = 0.71) and acidity(r = 0.55). Potassium correlated negatively with TSS (r = 0.91) andacidity (r = 0.55), whereas Ca (r = 0.61) correlated positively withjuice content and negatively with rag (r = 0.39) and rind (r = 0.63)contents.

Among micronutrient contents in 3-year-old plants, rind con-tent correlated negatively with Cu (r = 0.91) and Zn (r = 0.98), ragcontent correlated negatively with Fe (r = 0.76) and Zn (r = 0.80),and acidity correlated positively with Fe (r = 0.76) and Zn (r = 0.90)(Table 5). In 6-year-old trees, rag content correlated positively withMn (r = 0.71). Irrespective of tree age, Mn correlated negatively withjuice (r = 0.51), rag (r = 0.59) and rind (r = 0.77) contents, whereas



Fig. 2. Internal physical parameters of ‘Kinnow’ mandarin affected by tree age and canopy position (n = 10).

Table 1Internal fruit quality of ‘Kinnow’ mandarin affected by tree age and canopy position.

Tree age (years) TSS (%) Acidity (%) TSS:acidity Ascorbic acid (mg/100 mL)

ECPa ICPb Mean ECP ICP Mean ECP ICP Mean ECP ICP Mean

3 10.3b 10.3b 10.3AB 0.77b 0.77b 0.77B 13.5a 13.5a 13.5A 32a 32a 32A6 10.9ab 8.9d 9.9AB 0.88ab 0.69b 0.78AB 12.7a 12.9a 12.8AB 32a 28ab 30A18 11.2a 9.6c 10.4A 0.99a 0.83ab 0.92A 11.3a 11.6a 11.4B 30ab 25a 27.5AB35 10.5b 9.3 cd 9.9B 0.81a 0.84ab 0.83AB 12.8a 11.3a 12.1AB 27ab 23b 25B

Mean 10.7A 9.5B 0.86A 0.79A 12.5A 12.3A 29A 28.3A

Different letters indicate significant differences between means (P ≤ 0.05).a External canopy position.b Internal canopy position.

Table 2Biochemical parameters of ‘Kinnow’ mandarin affected by tree age and canopy position.

Tree age (years) pH Reducing sugars (%) Non-reducing sugars (%) Total sugars (%)

ECPa ICPb Mean ECP ICP Mean ECP ICP Mean ECP ICP Mean

3 3.07a 3.07a 3.07A 1.83bc 1.82bc 1.83C 5.85a 5.85a 5.85A 7.59b 7.59b 7.59AB6 2.70c 3.00ab 2.85B 2.49a 1.57c 2.03B 5.57abc 5.06c 5.31B 7.94ab 6.54d 7.24C18 2.47d 2.70c 2.58C 2.59a 1.89b 2.24A 5.76ab 5.24bc 5.50AB 8.21a 7.04c 7.63A35 2.87bc 2.97ab 2.92B 2.04b 1.59c 1.82C 5.75ab 5.37abc 5.55AB 7.69b 6.88cd 7.28BC

Mean 2.78B 2.94A 2.24A 1.72B 5.73A 5.38B 7.86A 7.01B

Values not sharing the common letters are statistically significant at 5% level of significance.aExternal canopy position.bInternal canopy position.



Fig. 3. Rind macronutrient contents affected by tree age and canopy position (n = 10).

Mn correlated positively with acidity (r = 0.41). TSS correlated neg-atively with Cu (r = 0.35) and Fe (r = 0.35).

4. Discussion

Fruit quality, specifically external appearance, is one of the mostimportant criteria when purchasing fruit. External fruit quality islargely determined by rind colour, smoothness and texture. Thisstudy revealed that fruit from very young ‘Kinnow’ trees (3-year-old) were poor in external, internal and biochemical parameterscompared to those of other age groups. Similar results were

reported for oranges (Frometa and Echazabal, 1988; Hearn, 1993)and ‘Satsuma’ mandarin (Matsumato et al., 1972). Fruit from oldtrees (35-year-old) had slightly inferior quality as compared to fruitproduced from 18-year-old trees. A similar trend was reported forapples (Smith, 2003; Tahir et al., 2007). Rind calcium (Ca) contentcorrelated negatively with rind thickness which is consistent withthe findings of Ali et al. (2000) in the case of ‘Navel’ orange. Forrind macronutrient contents, Ca was lower in younger than in oldertrees. The findings that the Ca content of mandarin rinds generallyincreased with tree age closely reflect results found for avocadofruit (Snijder et al., 2002). In mature ‘Navel’ orange trees, Ca content

Fig. 4. Rind micronutrient contents affected by tree age and canopy position (n = 10).



Table 3Rind nutrient contents and rind quality in relation to tree age and canopy position.

Rind quality Tree age (years) Macronutrients Micronutrients

Nitrogen (N) Phosphorous (P) Potassium (K) Calcium (Ca) Copper (Cu) Manganese (Mn) Iron (Fe) Zinc (Zn)

Rind thickness(mm)

3a −0.47NS −0.74* +0.38NS −0.79* −0.92* −0.75* −0.85* −0.80*

6a +0.22NS −0.52NS −0.73* −0.10NS −0.07NS −0.47NS −0.33NS −0.3NS

18a −0.07NS −0.0NS −0.10NS −0.13NS +0.04NS −0.27NS +0.43NS −0.16NS

35a −0.20NS −0.30NS −0.3NS −0.4NS +0.12NS −0.39NS −0.28NS +0.21NS

Meanb −0.30NS −0.3NS −0.2NS −0.59* −0.04NS +0.27NS +0.15NS +0.01NS

Rind smoothness(scores)

3a +0.30NS +0.52NS −0.43NS −0.44NS −0.38NS −0.52NS −0.23NS +0.07NS

6a −0.01NS +0.28NS +0.25NS −0.30NS +0.16NS −0.29NS −0.34NS −0.62NS

18a −0.74* +0.37NS +0.52NS +0.33NS +0.5NS +0.19NS −0.097NS −0.70NS

35a +0.69NS +0.65NS 0.18NS −0.28NS −0.57NS +0.43NS +0.50NS +0.10NS

Meanb +0.50* +0.42* +0.19NS +0.50NS −0.3NS −0.45* −0.2NS −0.23NS

NS = non significant.a N = 8, r = 0.71.b N = 32, r = 0.35.

was initially lower in fruit harvested during stage I and increasedduring stage II and III of fruit development (Storey and Treeby, 2000,2002). Lower Ca content in the rinds of young trees might be due totheir vigorous growth habit. Fruit harvested from vigorous avocadotrees contained less Ca compared to non-vigorous trees (Whitneyet al., 1990). It is well known that Ca plays an important role incell to cell arrangement. Exogenous application of Ca reduced theintercellular spaces in ‘Satsuma’ mandarin rind tissues resultingin compact and homogenous arrangements of cells compared tothat of untreated control fruit (Shiraishi et al., 1999). In fruit har-vested from young trees, low rind Ca content might be the reasonfor irregular arrangement of cells resulting in more rind thicknessand coarseness.

The rind nutrient profile of young trees showed higher micronu-trient (Zn, Mn, Cu and Fe) contents and lower macronutrients (N, P,K and Ca). This might be due to the difference in mobility of thesenutrients as N, P and K are phloem mobile, whereas Ca, Zn, Mn, Cuand Fe are xylem mobile nutrients (Storey and Treeby, 2002). Youngcitrus plants may have better mobility of xylem mobile nutrients,since it has been reported that xylem conductivity decreases with

increasing tree age (Hubbard, 1999), and accumulation of micronu-trients in the rind of fruit from older trees also decreased. Howeverin young trees, lower rind Ca content (xylem mobile nutrient) mightbe due to mobilization of Ca from a limited pool which is storedin fruit trees (Ferguson, 1980). Similar results for Fe content werereported by Asrey et al. (2007) who noticed that fruit from youngguava trees contain higher Fe content, but they found low Mn con-tent in fruit of young guava trees which is contradictory to ourfindings where Mn contents are higher in young (3-year-old) trees.Poor fruit quality in young trees might be due to their vigorous veg-etative growth resulting in reduced assimilates being supplied tothe reproductive organs, especially fruit. This study indicates thattree age consideration is a wise approach to determine citrus fer-tilizer needs for quality fruit production. In young trees, providingneeded nutrients (N, P, Ca, etc.) in adequate quantities, may resultin the improvement in their fruit quality.

External fruit quality parameters significantly correlated withrind nutrient contents. However, in variance with our results forK, Morgan et al. (2005) and Ali et al. (2000) reported a directcorrelation between K and rind thickness in ‘Hamlin’ and ‘Navel’

Table 4Effect of macronutrients on internal fruit quality of ‘Kinnow’ mandarin in relation to tree age.

Macronutrients Tree age (years) Internal fruit quality

Juice mass (%) Rag mass (%) Rind mass (%) TSS Acidity (%)

Nitrogen (N)

3a +0.70NS −0.96* −0.65NS −0.67NS +0.44NS

6a −0.2NS −0.03NS +0.24NS +0.30NS +0.31NS

18a +0.41NS −0.63NS −0.13NS +0.35NS +0.49NS

35a +0.25NS −0.36NS −0.13NS −0.74* −0.10NS

Meanb +0.29NS +0.01NS −0.38* +0.16NS +0.44*

Phosphorous (P)

3a +0.04NS −0.36NS −0.24NS +0.18NS +0.52NS

6a +0.48NS +0.31NS −0.74* −0.09NS +0.19NS

18a +0.51NS +0.05NS −0.57NS −0.70NS −0.51NS

35a +0.37NS +0.29NS −0.44NS −0.56NS +0.10NS

Meanb +0.65* +0.21NS −0.27NS −0.71* −0.55*

Potassium (K)

3a −0.80* +0.99* +0.70NS +0.78* −0.42NS

6a +0.06NS +0.66NS −0.81* −0.92* −0.66NS

18a +0.33NS +0.42NS −0.53NS −0.59NS −0.46NS

35a −0.22NS +0.49NS +0.06NS −0.66NS −0.78*

Meanb +0.02NS +0.21NS −0.27NS −0.91* −0.55*

Calcium (Ca)

3a +0.21NS −0.51NS −0.38NS +0.06NS +0.61NS

6a −0.27NS +0.31NS −0.08NS +0.21NS −0.34NS

18a +0.3NS −0.15NS −0.37NS −0.62NS −0.46NS

35a −0.05NS +0.44NS −0.11NS −0.18NS −0.47NS

Meanb +0.61* −0.39* −0.63* −0.16NS +0.09NS

NS = non significant.a N = 8, r = 0.71.b N = 32, r = 0.35.* P < 0.05.



Table 5Effect of micronutrients on internal fruit quality of ‘Kinnow’ mandarin in relation to tree age.

Macronutrients Tree age (years) Internal fruit quality

Juice mass (%) Rag mass (%) Rind mass (%) TSS Acidity (%)

Copper (Cu)

3a +0.21NS −0.58NS −0.91* −0.00NS +0.99NS

6a +0.39NS −0.02NS −0.29NS +0.11NS +0.42NS

18a −0.14NS +0.22NS +0.02NS −0.25NS −0.41NS

35a +0.05NS −0.34NS +0.03NS +0.58NS +0.31NS

Meanb +0.19NS −0.01NS +0.27NS −0.35* −0.31NS

Manganese (Mn)

3a +0.05NS −0.36NS −0.24NS +0.19NS +0.52NS

6a −0.39NS +0.71* −0.44NS −0.60NS −0.61NS

18a −0.03NS −0.19NS +0.04NS −0.06NS 0.05NS

35a +0.78NS −0.64NS −0.55NS −0.22NS +0.65NS

Meanb −0.51* −0.59* −0.77* −0.20NS +0.41*

Iron (Fe)

3a +0.58NS −0.76* −0.70NS −0.20NS +0.76*

6a −0.42NS +0.50NS −0.19NS −0.57NS −0.55NS

18a −0.34NS +0.03NS +0.39NS +0.31NS +0.03NS

35a +0.56NS −0.63NS −0.39NS −0.60NS +0.19NS

Meanb −0.28NS +0.16NS +0.27NS −0.35* −0.31NS

Zinc (Zn)

3a +0.89NS −0.80* −0.98* −0.33NS +0.90*

6a −0.54NS +0.44NS +0.00NS −0.33NS −0.53NS

18a +0.44NS −0.51NS +0.44NS +0.33NS +0.47NS

35a −0.24NS −0.61NS +0.25NS −0.27NS −0.07NS

Mean +0.61* −0.10NS +0.11NS −0.09NS +0.02NS

NS = non significant.a N = 8, r = 0.71.b N = 32, r = 0.35.* P < 0.05.

oranges, respectively. Similarly Koo (1988) reported that increas-ing K rates increased rind thickness. These differences might be dueto the difference in climatic conditions, cultivars, tree age and ini-tial K leaf content. Similar to our findings, Ali et al. (2000) reporteda negative correlation between Ca content and rind thickness in‘Navel’ orange, whereas Morgan et al. (2005) reported no correla-tion between rind Ca content and rind thickness.

Internal fruit quality parameters were also significantly corre-lated with rind nutrient contents. Contradictory to our findings,Morgan et al. (2005) reported a significant positive correlationbetween rind K contents and fruit quality (higher juice content andlower TSS and acidity), whereas Morgan et al. (2005) found no cor-relation between fruit quality and rind P and Ca contents. Similarto our findings, Koo (1988) reported an increase in acidity withincrease in N. However, Koo’s findings for K were contradictory toour results. The differences in these results for K might be due todifferences in age of the plants, cultivars and climatic conditions.

TSS was higher in fruit from the external tree canopy. Simi-lar results were also reported for ‘Tarocco’ orange (Agabbio et al.,1999), ‘Red blush’ grapefruit (Syvertsen and Albrigo, 1980), and‘Kinnow’ mandarin, ‘Valencia’ orange and ‘Lisbon’ lemon (Fallahiand Moon, 1989). Fruit which were harvested from exteriorcanopy positions had significantly higher sugar content than fruitharvested form interior canopy positions. Similar results werereported for ‘Kinnow’ mandarin (Jawanda et al., 1973; Khan et al.,2009) and in orange (Uchida et al., 1985). However, Datio andTominaga (1981) observed no significant effect of fruit positionin the canopy on total sugar content in ‘Satsuma’ mandarin fruitjuice. This study shows that fruit position in the canopy plays animportant role in determining fruit quality of ‘Kinnow’ mandarinwhich is different in the internal and external tree canopy in termsof juice mass (%), rind mass (%), rind smoothness and thickness.Fruit obtained from external canopy had higher rind thicknessand rind mass (%) along with lower juice contents. This corre-lates with the high N contents and lower macro and micronutrients(except Cu) in fruit of external tree canopy. Higher N contents inECP might be due to more chlorophyll molecules in sun exposedleaves (Givnish, 1988) and fruit (during development). The N effect

in increasing rind mass (%), thickness and roughness and decreas-ing juice mass (%) have already been documented in literature(Saleem et al., 2008). Higher N contents in outer canopy positionswere also reported in apple (Smit, 2007) and peel of mangosteen(Pechkeo et al., 2007). Low macro and micro-nutrient contents inECP might be due to active photosynthesis (Prieto et al., 2010) andmore vegetative growth in this area resulting in competition amongvegetative and reproductive organs (fruit) for nutrients (Khumalo,2006). Concurrent findings were also reported for P and K in ‘Kin-now’ mandarin (Fallahi and Moon, 1989) and for micro-nutrientcontents in guava (Asrey et al., 2007).

5. Conclusions

Tree age has a pronounced effect on ‘Kinnow’ mandarin fruitquality as fruit from young trees (3-years-old) exhibited poor fruitquality in terms of thick and coarse rinds with more rag and rindpercentage and lower juice quality. Moreover, rinds of fruit fromyoung trees also had lower macro- (N, P and Ca) and higher micro-nutrient (Mn and Fe) contents. In young trees, macronutrients (Pand Ca) and micronutrients (Cu, Mn, Fe and Zn) showed a negativecorrelation with fruit rind thickness, and offer potential for improv-ing fruit quality in young orchards by incorporating these nutrientsin a balanced nutritional program. In consideration of where fruitare borne in a tree’s canopy, internal canopy fruit showed betterquality and higher rind nutrient contents (P, K and Mn) than fruitfrom external canopy.

Acknowledgements

We acknowledge the financial assistance of the Higher Edu-cation Commission (HEC), Islamabad, Pakistan, for these studiesunder the 5000 Indigenous PhD Fellowship Scheme. We arealso thankful to Dr. Graham Barry (The XLnT Citrus Company,Helderberg, South Africa) for critically reviewing the manuscriptand improvement.



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Tree age canopy position affect rind quality, fruit quality and rind nutrient contents

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