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FOLIAR APPLICATION OF BORONINFLUENCES THE LEAF MINERAL STATUS,VEGETATIVE AND REPRODUCTIVEGROWTH, YIELD AND FRUIT QUALITYOF ‘KINNOW’ MANDARIN (CITRUSRETICULATA BLANCO.)S. Ullah a , A. S. Khan a , A. U. Malik a , I. Afzal b , M. Shahid c & K.Razzaq aa Institute of Horticultural Sciences, University of Agriculture,Faisalabad, Pakistanb Department of Crop Physiology, University of Agriculture,Faisalabad, Pakistanc Department of Chemistry and Biochemistry, University ofAgriculture, Faisalabad, PakistanAccepted author version posted online: 14 Aug 2012.Publishedonline: 05 Oct 2012.

To cite this article: S. Ullah , A. S. Khan , A. U. Malik , I. Afzal , M. Shahid & K. Razzaq (2012):FOLIAR APPLICATION OF BORON INFLUENCES THE LEAF MINERAL STATUS, VEGETATIVE ANDREPRODUCTIVE GROWTH, YIELD AND FRUIT QUALITY OF ‘KINNOW’ MANDARIN (CITRUS RETICULATABLANCO.), Journal of Plant Nutrition, 35:13, 2067-2079

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Journal of Plant Nutrition, 35:2067–2079, 2012Copyright C© Taylor & Francis Group, LLCISSN: 0190-4167 print / 1532-4087 onlineDOI: 10.1080/01904167.2012.717661

FOLIAR APPLICATION OF BORON INFLUENCES THE LEAF

MINERAL STATUS, VEGETATIVE AND REPRODUCTIVE GROWTH,

YIELD AND FRUIT QUALITY OF ‘KINNOW’ MANDARIN

(CITRUS RETICULATA BLANCO.)

S. Ullah,1 A. S. Khan,1 A. U. Malik,1 I. Afzal,2 M. Shahid,3 and K. Razzaq1

1Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan2Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan3Department of Chemistry and Biochemistry, University of Agriculture, Faisalabad, Pakistan

� The effects of foliar application of boron (B) in the form of boric acid on vegetative and re-productive growth, yield and fruit quality of ‘Kinnow’ mandarin (Citrus reticulate Blanco.) wereinvestigated. Kinnow mandarin was sprayed with different concentrations of boric acid viz. (0.1%,0.2%, 0.3% and 0.4%) at fruit set stage. Leaf nitrogen (N), phosphorus (P), potassium (K), B,and zinc (Zn) along with flush length, tree height, tree spread and tree trunk diameter increased,while leaf length and leaf age showed non-significant results after foliar B application. Yield of the‘Kinnow’ mandarin was significantly affected by foliar application of B and a significant increasein fruit weight at harvest was also observed. Soluble solid concentration (SSC): titratable acidity(TA) ratio, ascorbic acid, total sugars, total phenolic content (TPC) and total antioxidants signifi-cantly affected, while pH of juice, SSC, TA, reducing sugars and non-reducing sugars showed non-significant results.

Keywords: boron, Citrus reticulata Blanco, foliar application, fruit quality, ‘Kinnow’

INTRODUCTION

Among different species of citrus, ‘Kinnow’ (Citrus reticulate Blanco.) isthe leading citrus fruits grown in the Pakistan and is considered the most pop-ular citrus fruit. Out of the total area under citrus cultivation, about 65% isallocated for ‘Kinnow’ production (Mustafa and Ahmad, 2006). In 2006, Pak-istan exported 1348 tons of citrus fruit of worth US$ 300,000 (Anonymous,2009). Although macronutrients occupy a major role in citrus nutrition butmicronutrients are also essential for vegetative and reproductive growth,yield and fruit quality of citrus. Boron (B) as a micronutrient is a part and

Received 11 October 2010; accepted 21 March 2011.Address correspondence to S. Ullah, Institute of Horticultural Sciences, University of Agriculture,

Faisalabad 38040, Pakistan. E-mail: amiullah05@gmail.com

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parcel of the growth behavior and productivity of citrus trees. It increasespollen grain germination, pollen tube elongation, consequently fruit setpercentage and finally the yield (Abd-Allah, 2006), and in B deficient plantsthese processes may be severely impaired (Agarwala et al., 1981). However,when deficiency occurs it causes rapid cell division and early enlargementdue to clear limitation of its phloem mobility. This results in reduced growthof new roots, shoots and young fruit (Dugger, 1983; Shelp, 1993). The re-quirement of B for dicotyledous plants is higher than that of any othermicronutrient (Marschner, 1995). It is different from other micronutrientsbecause it has very narrow threshold between deficiency and toxicity (Yuaand Ryan, 2008). Its deficiency is a nutritional disorder, which decreasesplant growth and productivity ultimately the yield and fruit quality in aridand semiarid environments in citrus growing areas of the world (Papadakiset al., 2003; Goldberg, 1997). The deficiency of B worldwide is more exten-sive than that of any other micronutrient (Blevins and Lukaszewski, 1998).Its deficiency is one of the main factors to limit the improvement of yield andquality of the fruits (Meng and Wu, 1995; Wu et al., 1992), including citrus(Shorrocks, 1997). Therefore, the objective of this work was to investigatethe effects of foliar application of B on vegetative and reproductive growth,yield and fruit quality of ‘Kinnow’ mandarin.

MATERIALS AND METHODS

Cultural Conditions and Treatments

This trial was carried out at Experimental Fruit Orchard, Institute ofHorticultural Sciences, University of Agriculture, Faisalabad on nine-yearsold Kinnow mandarin trees (Citrus reticulata Blanco.) budded on RoughLemon (Citrus jambhiri L.) rootstock grown under uniform soil conditions.The experimental trees were planted according to square system of layoutat 6.1 m distance.

All trees were subjected to the same cultural practices such as irrigation,weeding, insect pest and disease control during the experiment. Twentyhealthy trees uniform in size and vigor were selected for the trial. Foliarapplications of B in the form of 0.1, 0.2, 0.3 and 0.4% boric acid wereapplied to the trees at fruit set stage. Control trees sprayed with distilledwater. Tween-20 at 0.01% was added in spray solution as a surfactant. Theexperiment was carried out according to randomized complete block designand a single tree was used as a treatment unit replicated four times.

Sampling and Measurements

Fifty 5–7 month-old leaves from non-fruiting terminals of spring growthcycle were randomly collected before and after the B application. Leaf sam-ples were washed with tap water, then with distilled water and dried at 70◦C

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Response of Kinnow to Foliar Application of B 2069

until constant weight, finally, ground and acid digested. The digested solu-tion was used for the determination of each of nitrogen (N) using microKjeldhal method, phosphorus (P) by vanadomolybdo method, and potas-sium (K) was determined by flame photometer according to the methoddescribed by Chapman and Parker (1961). Various metal elements [zinc(Zn), manganese (Mn), calcium (Ca), and iron (Fe)] were determined onatomic absorption spectrophotometer (2–8200 Series Polarized Zeeman, Hi-tachi, Tokyo, Japan) by using specific lamp for specific nutrient. The B inleaf samples was determined by dry ashing as reported earlier by Chapmanand Pratt (1961), and subsequent measurement of B was done throughcolorimetry Azomethine-H as outlined by Bingham (1982).

Conventional methods were employed to record the growth parametersof trees. Number of fruits per plant at spray time and after spray was countedby tagging four branches two inches in diameter on each side of the tree. Tocalculate fruit drop from tagged branches of the experimental tree, numberof fruits were counted and fruit drop percentages were calculated accordingto Khan et al. (2009). Yield per tree was recorded by weighing and count-ing total number of fruits per tree at harvest time. Fruit size was measuredby measuring the diameter of 10 fruits per tree randomly with the help ofVernier caliper from each experimental tree. Total numbers of under sizedfruit (less than 6 cm diameter) were also counted per treatment and percent-age of unmarketable fruit was calculated dividing the number of under sizefruit to total fruit and then multiplied by 100. Juice of the 10 selected fruit wasextracted and weighed then average juice weight was calculated separatelyfor each treatment expressed in%. Soluble solids concentration (SSC) wasdetermined by automatic digital refractometer (ATAGO, RX 5000; AtagoInc., Tokyo, Japan) by placing 1–2 drops of juice on the prism of refractome-ter. Titratable acidity (TA) of juice was determined by titrating against 0.1Nsodium hydroxide (NaOH) and was expressed as percent citric acid (%).Ascorbic acid in juice was estimated according to the method described byRuck (1961) whereas sugars in juice were estimated by using the methoddescribed by Hortwitz (1960). Total phenol content of the extract was de-termined by the Folin-Ciocalteu method (Singleton and Rossi, 1965), usinggallic acid as the standard. The concentration of total phenolics was ex-pressed as the gallic acid equivalent (GAE mg g-1) of the lyophilized sample(Satisha et al., 2008). The DPPH free radical scavenging activity of antioxi-dants were measured by bleaching the purple- colored ethanol solution ofthe stable DPPH radical, according to the method reported by Blois (1958)with some modification (Koksal and Gulcin, 2008).

Statistical Analysis

The data collected were statistically analyzed using the computer soft-ware using MSTAT- C (Crop and Soil Science Department, Michigan StateUniversity, East Lansing, MI, USA.). Analysis of variance techniques were

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employed to test the overall significance of the data, while the least signif-icant difference (LSD) test (P ≤ 0.05) was used to compare the treatmentmeans (Steel et al., 1996).

RESULTS AND DISCUSSION

Leaf N, P and K

The levels of N, P and K before foliar application of B in the Kinnow’mandarin leaves were between 1.91–2.14%, 0.09–0.10% and 0.26–0.33%, re-spectively. Foliar application of B brought a significant increase in leaf N(1.96–2.31%), P (0.1–0.113%) and K (0.34–0.44%) levels of sprayed ‘Kin-now’ mandarin trees as compared to control trees (Figure 1). After foliarapplication of B the levels of both N and P were still at the low range from1.96 to 2.31% and 0.1 to 0.113% respectively, whilst K was from deficient to

FIGURE 1 Effects of foliar application of B (in the form of boric acid) on N, P and K contents of‘Kinnow’ mandarin leaves. Vertical bars represent the ± SE of the means.

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Response of Kinnow to Foliar Application of B 2071

low range 0.34 to 0.44%. Trees sprayed with 0.3% boric acid showed highestincrease in N level (2.31%) about 15-fold higher than unsprayed trees. Afterthe foliar application of boric acid the leaf N contents of ‘Kinnow’ mandarintrees increased but still remain in low range, which were in deficient rangebefore foliar application of boric acid.

These results were in line with Abd-Allah (2006) who stated that boricacid application in combination of potassium citrate increased the N contentof the leaves of Washington Navel orange. The trees sprayed with 0.3% boricacid revealed maximum increase in leaf P contents of ‘Kinnow’ mandarintrees (0.113%) about 11% higher than control trees. The P level of ‘Kinnow’mandarin trees also found in low range after foliar application of B. Theresults was in line with earlier study of Salem et al. (1995) who observeda significant increase in P contents of Balady mandarin leaves with foliarapplication of Zn, B, and Mn. The highest leaf K contents were exhibitedby the foliar application of 0.2% boric acid about 23% higher than treessprayed with 0.3% boric acid, because low levels of B are associated withincrease in K contents of plants (Gupta, 1979). Similarly, foliar applicationof B did not increase the leaf K contents of Cherry trees budded on ‘Gisela5’ root stock (Sotiropoulos et al., 2006).

Leaf Ca, B, Fe, Mn and Zn

The levels of Ca, B, Fe, Mn and Zn before foliar application of B inthe ‘Kinnow’ mandarin leaves were between 8.5–11.4%, 22.6–30 mg kg−1,152.5–162.2 mg kg−1, 37.2–40 mg kg−1 and 4.8–16.2 mg kg−1, respectively(Figure 2). Leaf Ca contents of ‘Kinnow’ mandarin was in excess, Fe inhigh, Mn in optimum, Zn in low and that of B was in deficient range beforethe foliar application of B. Foliar application of B brought a significant (P ≤0.05) increase in leaf B and Zn levels and non-significant (P ≤ 0.05) increasein Ca, Fe and Mn levels of sprayed ‘Kinnow’ mandarin trees as compared tocontrol trees.

The tress sprayed with 0.3% boric acid showed highest leaf Ca, Mn, andZn contents of ‘Kinnow’ mandarin, while foliar application of 0.4% and 0.2%boric acid exhibited the highest leaf B and Zn contents as compared to con-trol trees (Table 1). The Ca, Fe, Mn, and B contents of ‘Kinnow’ mandarinleaves showed an increase after the foliar application of B except leaf Mncontents. This might be due to negative interaction between B and Mn incrop plants (Zaharieva, 1986). These results was confirmed by Sotiropouloset al. (2006) in case of cherry rootstock in which the Mn contents of theleaves was found to decrease with foliar application of B. The leaf Zn wasincreased from low to optimum range by the foliar application of B, whichis supported by the findings of Leon et al. (1983) who stated that high B wasassociated with increased Zn in Lemon leaves. The leaf Ca was increased butat higher level of B it showed decreasing trend. These results confirm the

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FIGURE 2 Effects of foliar application of B (in the form of boric acid) on B and Zn contents of ‘Kinnow’mandarin leaves. Vertical bars represent the ± SE of the means.

findings of Sotiropoulos et al. (1999) who stated that by increasing B the Cacontent of the leaves was increased at a certain level but became reduced attoxic levels of B in Kiwifruit. The leaf B content was increased from deficientto higher level as results of foliar application of B.

Vegetative Growth

The foliar application of B significantly affected the vegetative growthparameters of ‘Kinnow’ mandarin tree. Tree height, spread, stem diameter,flush length and leaf width was significantly increased by the foliar applica-tion of B (Table 2). Trees sprayed with 0.3% boric acid revealed the highest

TABLE 1 Effects of foliar application of B (in the form of boric acid) on the micronutrients of‘Kinnow’ mandarin leaf

Before application After applicationTreatment(% boric acid) Ca (%) Fe (mg Kg-1) Mn ( mg Kg-1) Ca (%) Fe ( mg Kg-1) Mn ( mg Kg-1)

Control 8.54 162.00 37.50 9.58 169.00 35.750.1 11.43 160.50 37.25 9.97 166.50 32.250.2 11.26 152.50 37.75 11.47 233.25 32.750.3 9.88 158.25 40.00 12.61 196.25 35.750.4 11.34 162.25 40.00 9.92 214.00 35.75LSD (P ≤ 0.05) ns ns ns ns ns ns

ns represents not significant at P ≤ 0.05.

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Response of Kinnow to Foliar Application of B 2073

TABLE 2 Effects of foliar application of B (in the form of boric acid) on vegetative growth of ‘Kinnow’mandarin tree

Treatment Increase in Increase in Increase in Leaf length Increase in(% boric acid) tree height (cm) tree spread (cm) trunk diameter (cm) (cm) flush size (cm)

Control 16.23b 25.70a 3.18c 6.50 4.37b0.1 20.34a 21.44b 3.81ab 6.82 3.83b0.2 15.73b 25.54a 4.13ab 6.68 5.38a0.3 22.36a 18.38c 4.31a 6.68 5.43a0.4 20.17a 21.21b 3.63bc 6.70 4.56bLSD (P ≤ 0.05) 2.404 2.193 0.594 ns 0.734

ns represents not significant at P ≤ 0.05. Any two means within a column followed by the same letterare not significant at (P ≤ 0.05).

increase in the tree height and flush length of ‘Kinnow’ mandarin as com-pared to control, while trees sprayed with 0.4% and 0.1% boric acid showedmaximum increase in stem diameter and leaf size than control trees. Treespread was maximum in case of control trees followed by trees sprayed with0.2% boric acid, while minimum was 0.3% application of boric acid. Thismight be due to the reason that foliar application of B has been reported toreduce the biomass production in tomato, onion and celery when it is ap-plied as foliar spray at higher concentrations, it had negative effects on plantgrowth (Ben-Gal, 2007). Foliar application of B significantly increased theflush length of ‘Kinnow’ mandarin tree, this might be due to the increasedphotosynthetic rates of the plant sprayed with B. Our results were at par withthe findings of Cifu et al. (2007) reported that the spring shoot length andsummer shoot length were increased with increasing B rates in red bayberry.

Fruit Drop (Percentage)

The maximum total fruit drop percentage (87%) was observed by thefoliar applications of 0.2% and 0.4% boric acid, while the minimum wasrecorded in case of trees sprayed by 0.1% boric (75%), while control treesand those sprayed with 0.3% boric acid showed 84% and 85% total fruitdrop percentage, respectively (Figure 3). The trees that were treated with0.1% boric acid spray showed about 10% less total fruit drop than control.The trees sprayed with 0.1% boric acid, with simple water (control) andwith 0.4% boric acid showed the least pearl, June and pre-harvest drops of‘Kinnow’ mandarin fruit, respectively. The maximum pearl and June fruitdrop was recorded in the trees sprayed by 0.4% boric acid, and of pre-harvest drop in case of the trees sprayed by 0.1% boric acid (Figure 3).The reason might be that boric acid acted as insecticide for the attack offruit fly which is a major cause of pre-harvest drop in ‘Kinnow’ mandarin,while it’s higher concentration become toxic for the plant by disruptingphotosynthesis because there is very narrow range between optimum and

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FIGURE 3 Effects of foliar application of B (in the form of boric acid) on pearl drop, June drop,pre-harvest drop and total drop of ‘Kinnow’ mandarin fruit. Vertical bars represent the ± SE of themeans.

toxicity of B. The results are in line with the findings of Singh and Singh(1973) who reported that foliar application of urea in combination of Breduced the proportion of fruit drop in ‘Kaghzi’ lime.

Fruit Yield (Fruit Numbers and Weight)

Foliar application of B did not significantly affect the yield of ‘Kinnow’mandarin. Trees sprayed with 0.2% boric acid exhibited highest increasein the fruit yield both in terms of average fruit number and average fruitweight per tree as compared to control (Table 3). Percentage of marketablefruit in the trees sprayed by 0.3% boric acid was 29% more as comparedto untreated control fruit. Foliar spray of potassium citrate and boric acidhad been reported to increase fruit set, fruit retention and consequently theyield as weight or number of fruits per tree in mango (Saleh et al., 2003).

TABLE 3 Effects of foliar application of B (in the form of boric acid) on reproductive growth of‘Kinnow’ mandarin tree

YieldMarketable fruit Unmarketable fruit

Treatment Weight Number(% boric acid) (kg) (no.) No. % No. %

Control 44.6 219.5 226.2c 13.02b 94.56d 5.44b0.1 45.3 213.5 259.8bc 12.97b 95.25a 4.76e0.2 50.9 244.8 290.3ab 16.15b 95.04b 4.96d0.3 50.7 233.0 320.5a 19.05a 94.39e 5.61a0.4 47.7 235.5 271.5b 14.70b 94.85c 5.15cLSD (P ≤ 0.05) ns ns 44.99 2.357 0.128 0.129

ns represents not significant at P ≤ 0.05. Any two means within a column followed by the same letterare not significant at (P ≤ 0.05).

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Response of Kinnow to Foliar Application of B 2075

As the levels of foliar application of boric acid increased the yield (numberof fruit per tree and weight of fruit per tree) of ‘Kinnow’ mandarin was alsoincreased, this might be due to increased fruit set and fruit retention by theB. Our results were supported by Abd-Allah (2006) who stated that foliarapplication of boric acid and calcium chelate produced the highest numberof fruits in ‘Washington’ navel orange.

Fruit Quality

Foliar application of B significantly affected the fruit weight and volumeof ‘Kinnow’ mandarin but rind thickness was not affected by the foliar appli-cation of B (Table 4). Trees sprayed with 0.1% boric acid showed the highestweight, volume and rind thickness of ‘Kinnow’ mandarin fruit as comparedto control.

Number and weight of seeds of ‘Kinnow’ mandarin fruit were not af-fected significantly by the foliar application of B (Table 4). However, treessprayed with 0.2% boric acid showed the highest number of ‘Kinnow’ man-darin seeds per fruit, while foliar application of 0.3% boric acid revealed thehighest weight of ‘Kinnow’ mandarin seeds per fruit as compared to control(Table 4).

Foliar application of B significantly affected the juice percentages whilethe peel and rag percentage was not significantly affected by the foliar appli-cation of B. Foliar applications of 0.1%, 0.2% and 0.3% boric acid recordedthe highest value for peel, juice and rag weight percentages respectively. Theresults of juice weight percentage of ‘Kinnow’ mandarin fruit was in line withthe findings of Abd El-Migeed et al. (2000) who found a significant increasein the juice weight of ‘Hamlin’ orange by the spray of P in combinationwith B.

Foliar application of B significantly affected the titratable acidity (TA),SSC:TA and ascorbic acid contents of ‘Kinnow’ mandarin fruit while SSCwas not significantly affected by the foliar applications of B (Table 5). Thetrees sprayed with 0.3% boric acid revealed the maximum TA, while 0.4%foliar application of boric acid gave the maximum results in case of SSC:TAas compared to control. Fruit harvested from control trees exhibited themaximum level of ascorbic acid as compared to other treatments. B playsan important role in the biosynthesis of auxin in the plant meristem andits deficiency leads to increase in the level of bound auxin and reductionin the indole acetic acid (IAA)-oxidase activity (Dugger, 1973). As a resultof increased levels of bound auxin the ascorbic acid content of the fruitwas increased. Therefore the increased ascorbic acid content of the controltrees might be due to increased level of bound auxin which is produce inabsence of B. Trees applied with foliar application of 0.2% boric acid hadthe highest SSC of ‘Kinnow’ mandarin fruit as compared to control. Ourresults confirmed the finding of Mishra et al. (2003) who stated that foliar

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Response of Kinnow to Foliar Application of B 2077

TABLE 5 Effects of foliar application of B (in the form of boric acid) on chemical quality of ‘Kinnow’mandarin fruit

Treatment SSC TA Ascorbic acid Total Reducing Non-reducing(% boric acid) SSC (%) TA (%) (ratio) pH (mg 100g−1) sugars (%) sugars (%) sugars (%)

Control 8.25 0.36ab 23.46b 5.98 46.33a 5.28b 2.51 2.90ab0.1 8.00 0.38a 20.89c 5.92 35.53b 5.25b 3.63 1.81c0.2 8.65 0.38a 22.83b 5.92 35.53b 5.65a 3.57 2.26bc0.3 8.20 0.40a 20.56c 5.89 43.42a 5.84a 2.93 3.06a0.4 8.10 0.33b 24.89a 5.95 42.11a 5.53ab 3.07 2.61abLSD (P ≤ 0.05) ns 0.049 1.49 ns 4.918 0.327 ns 0.779

ns represents not significant at P ≤ 0.05. Any two means within a column followed by the same letterare not significant at (P ≤ 0.05).

application of Zn + B treatment had the highest SSC in ‘Kinnow’ mandarinas compared to control.

Total sugars and non-reducing sugars were significantly affected by thefoliar application of B, while non-significant results were produced for thelevels of reducing sugars in ‘Kinnow’ mandarin fruit (Table 5). The treessprayed with 0.3% foliar application of boric acid revealed the highest totalsugars and non-reducing sugars as compared to control. The B facilitatesthe transport of sugars in the plants by making B complexes with these ele-ments or because it had an essential role in biosynthesis of auxin (Dugger,1973). So, the increase in the total sugar content of the foliar applied boricacid fruits might be due to the increased translocation of sugars in ‘Kinnow’mandarin. The trees sprayed with 0.1% boric acid showed the highest re-ducing sugars of ‘Kinnow’ mandarin fruit as compared to control. Reducingsugars are one of the B complex substances formed from furanose cis-diolstructure, which rarely occur in nature. At high B levels these structures donot occur, so due to high levels of B, reducing sugars tend to decrease (Xuet al., 2005). The decrease in reducing sugars of juice of ‘Kinnow’ mandarinmight be due to absence of furanose cis-diol structure at higher levels of B.

Total phenolic contents and total antioxidants were significantly affectedby the foliar application of B for ‘Kinnow’ mandarin fruit (Figure 4). Thetrees, where no application of boric acid was done revealed the highest totalphenolic contents while the least reading was noted in the trees sprayedwith 0.3% boric acid (Figure 4). The phenolic compounds tend to increasein the B deficient plants and the defence capacity of cells against toxic re-active oxygen species is weakened due to reduced levels of ascorbic acid,SH-compounds and hydrogen peroxide (H2O2) scavenging enzymes (Cak-mak, 1994; Cakmak and Romheld, 1997). The total antioxidants activity wassignificantly affected by the foliar application of B. Maximum antioxidantactivity was noted in the fruit juice of the ‘Kinnow’ mandarin tree whichwas sprayed by 0.3% boric acid, while the minimum was noted in controltreatment.

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FIGURE 4 Effects of foliar application of B (in the form of boric acid) on level of total antioxidants andphenolic compounds in ‘Kinnow’ mandarin fruit. Vertical bars represent the ± SE of the means.

ACKNOWLEDGMENTS

Sami Ullah and Kashif Razzaq gratefully acknowledge the Higher Edu-cation Commission of Pakistan for granting Indigenous PhD Fellowships.

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