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Scientia Horticulturae 138 (2012) 90–95

Contents lists available at SciVerse ScienceDirect

Scientia Horticulturae

journa l homepage: www.e lsev ier .com/ locate /sc ihor t i

ole of lenticel morphology, frequency and density on incidence of lenticelreakdown in ‘Gala’ apples

.S. Turketti a, E. Curryb, E. Lötzea,∗

Department of Horticultural Science, Stellenbosch University, Private Bag X1, 7602 Matieland, South AfricaTree Fruit Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Wenatchee, WA 98801, United States

r t i c l e i n f o

rticle history:eceived 16 November 2011eceived in revised form 1 February 2012ccepted 4 February 2012

eywords:

a b s t r a c t

Lenticel breakdown is a skin disorder of apples occurring around the globe. Symptoms of this physiologicaldisorder can be observed only after harvest. Prevalent on the variety ‘Gala’, especially ‘Royal Gala’, it isalso observed on the varieties ‘Fuji’, ‘Granny Smith’, ‘Golden Delicious’ and ‘Delicious’. Lenticel breakdownis influenced by a combination of factors that include cultivation and handling practices, however thecauses have not yet been determined. The motivation for the present research was to investigate the

enticel breakdownpples

Royal Gala’Gala’ sportsre-harvest

morphology and anatomy of lenticels, evaluating fruits at different stages of development. Fruits wereevaluated from three different orchards in the Western Cape, South Africa, on an attempt to relate physicaland morphological aspects of the fruit to the environment of the different regions. There is an indicationthat factors that influence fruit growth and cuticle development, e.g. relative humidity and temperature,are directly linked to lenticel breakdown. The lack of lenticel breakdown on the seasons studied limited

icroclimateouth Africa

our conclusions.

. Introduction

The term ‘lenticel’ was first used by Clements (1935) to indi-ate the white, green, or yellowish-brown spots common on theurface of apples (Malus domestica Borkh.). In general, lenticels aremall lenticular-shaped openings distributed evenly across the fruiturface that are formed as the cuticle develops over vestigial sto-ata during the early stages of fruit development (Clements, 1935;

urry, 2003). The fruit cuticle is a dynamic tissue, capable of main-aining optimum thickness to accommodate fruit enlargement asells within the fruit divide and expand (Curry, 2003, 2005). Underypical environmental conditions, this cuticle expansion processccurs gradually by a self-repair mechanism to prevent exposuref the underlying cells (Curry, 2003).

Lenticels vary in size due to development and position on theruit and are more or less open to the atmosphere. The base ofhe lenticel is covered with cuticle; however, it is often thinnerhan that of surrounding tissue (Curry, 2005). Harker and Ferguson1988) recorded that the dimensions and permeability of lenticelsncrease during fruit development. They also related lenticel size

ith calcium and water uptake in apples (Harker and Ferguson,988). Furthermore, they reported an increase in lenticel size late

n the developmental phase associated with cracks and small flaws

∗ Corresponding author. Tel.: +27 218083263; fax: +27 218082121.E-mail addresses: san@sun.ac.za (S.S. Turketti), eric.curry@ars.usda.gov

E. Curry), elotze@sun.ac.za (E. Lötze).

304-4238/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.scienta.2012.02.010

© 2012 Elsevier B.V. All rights reserved.

in the cuticle and concluded that increases and decreases in lenticelsize is a continuing process, therefore agreeing with Curry’s (2009)theory of cuticle repair (Harker and Ferguson, 1988).

In apples, the number of lenticels per fruit remains constant formost of the growing season, while the density declines graduallyas the fruit enlarges (Harker and Ferguson, 1988; Li et al., 2004). In‘Starkrimson’ and ‘Golden Delicious’, lenticel density was reportedto be negatively related to anthocyanin accumulation (Li et al.,2004). According to Clements (1935), the number of lenticels seemsto vary according to variety, for example ‘Delicious’ has an averageof 803 lenticels per apple, ‘Golden Delicious’ 843 lenticels ‘Stark-ing Delicious’ 1313 lenticels and ‘Red Delicious’ 1379 lenticels. Inaddition, within a variety the number of lenticels per apple varieswidely among fruit. In ‘Winesap’, the number of lenticels per fruitwas reported to range from 450 to 800 (Clements, 1935), whereasin ‘Granny Smith’, the number per fruit ranged from 655 to 870(Harker and Ferguson, 1988).

Lenticel breakdown is a skin disorder of apples that manifestsafter the fruit have been packed (Curry et al., 2008; Kupferman,2009a). It appears as a round pit centered on a lenticel and oftenoccurs on shaded sides or color margins of the fruit. Althoughprevalent on ‘Gala’ apples, especially ‘Royal Gala’, lenticel break-down has also been observed on ‘Fuji’, and to a lesser degree on‘Granny Smith’, ‘Golden Delicious’ and ‘Delicious’ (Curry, 2008).

Many factors have been associated with lenticel breakdown andgenerally they can be grouped as factors that occur before harvestand those postharvest. Factors influencing lenticel breakdownbefore harvest include the maturity of the fruit, mineral content

Horticulturae 138 (2012) 90–95 91

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nd orchard-specific responses. Although there is an affinity ofertain orchards to consistently have higher levels of lenticelreakdown, there is a strong year-to-year variation. Among theactors that occur after harvest, Kupferman (2009b) suggested thatelayed cooling, the use of SmartFresh, of soaps and detergents,ay positively affect lenticel breakdown incidence.In South Africa, various trials were conducted from 2007/8 to

010/11 in orchards that showed severe lenticel breakdown dur-ng 2004–2006 (Lötze and Theron, 2009), resulting in up to 50%oss in ‘Royal Gala’ exports (personal communication, P. Conradie,uToit Agri). These trials evaluated the influence of most aspectsited in literature known to influence lenticel breakdown incidence.n spite of extensive research the past few years, results regardinghe initiation or cause of lenticel breakdown in ‘Royal Gala’ were notonclusive mainly due to lack of lenticel breakdown manifestation.he present paper describes a new etiological approach: (1) a histo-ogical study of lenticel size on fruit at 40, 70 and 100 (commercialarvest) days after full bloom (dafb) and its relationship with earlyeason temperatures and (2) correlation of lenticel density withenticel breakdown development; with the presuppose that lenti-el breakdown incidence could be related to microclimate and fruitevelopment.

. Materials and methods

.1. Lenticel distribution and size in Western Cape, South Africa

.1.1. Using peel imprints to determine number and size ofenticels per cm2

‘Royal Gala’ apple fruits were sampled from three differentrchards in the Ceres area, Western Cape, South Africa, accord-ng to previous lenticel breakdown occurrences. In TandfonteinTFT – 32◦46′32.76S, 19◦14′25.86E) where lenticel breakdownas previously indicated as severe, Vastrap (VAS – 33◦15′10.40S,

9◦14′33.22E) where lenticel breakdown was previously indicateds moderate and Nooitgedaght (NGD – 33◦12′35.45S, 19◦19′50.24E)here lenticel breakdown was not present. Trees were all planted

n M793 rootstock and managed according to commercial prac-ices. Fruit were harvested at 40, 70 and 100 dafb (commercialarvest), comprising three treatments and three phenologicalhases of fruit development. Ten fruit of similar size were ran-omly selected from each site and each phenological stage. Printsere made from 1 cm2 peel sections of the fruit on the medianart, from the green (inside) and red (outside) sides of each fruit.he two sides were identified to address the possible influence ofeat and light exposure on lenticels number and size. The materialas prepared according to Wilson et al. (1981). Each imprint was

hen observed under a light microscope (Nikon Eclipse E 600, Nikonnstruments Europe B.V., Amstelveen, Netherlands) under 10 or 20imes magnification, to determine the number of lenticels per cm2.igital micrographs were taken of three lenticels per side per fruit

Nikon Digital Camera, DXM 1200C) and used to measure the widthnd length of each lenticel. The measurements were made with these of NIS Elements D 2.3 Program (Nikon Instruments). Mass andiameter were also recorded for each apple.

.1.2. Measuring length and depth of lenticels by cross-sectionsFrom the samples described above, 6 fruits were selected

andomly for microscopy studies. Lenticel cross-sections wereand-made of three lenticels from both sides of the fruit (green

nd red), placed on a microscope slide in a drop of water, coveredith slips and observed under a light microscope (Nikon Eclipse E

00) (Fig. 1). Digital micrographs were taken (Nikon Digital Cam-ra, DXM 1200C) and used to measure the depth and length of

Fig. 1. Cross-section of a lenticel used for anatomical measurements of A: lengthand B: depth. Bar is 100 �m.

each lenticel. The measurements were made with the use of NISElements D 2.3 Program (Nikon Instruments).

2.1.3. Lenticel development stagesBased on size and appearance, lenticels were classified accord-

ing to stages of development as ‘immature’, ‘intermediate’ and‘developed’.

2.2. Collection of temperature data

Hourly temperatures were collected from 2004/5, when thefirst severe lenticel breakdown incidence was reported at TFT to2010/11, using automatic weather stations. During 2009/10 to2010/11, similar data for NGD and VAS also became available.

2.3. Statistical analysis

Data were analyzed statistically using the PROC GLM procedurefrom the Statistical Analysis System (SAS) program (SAS InstituteInc., 2004, Cary, NC). Results were considered significantly differentusing the LSD of 5%.

2.4. Lenticel density and lenticel breakdown in ‘Gala’ sports inWashington State, USA

A preliminary study was initiated in 2009 in an experimentalorchard of 9-year-old‘Gala’ sports on Malling 26 rootstock growingin sandy loam near Orondo, WA (47◦33′54.33′′N, 120◦14′32.23′′W;elevation 289 m). ‘Gala’ sports included, ‘Brookfield’, ‘Pacific’,‘Royal’ and ‘UltraRed’ and were planted in a completely random-ized block design of three replications of seven trees. Although fruitset was generally heavy, hand thinning in late spring reduced cropload to a moderate level. Trees were irrigated by undertree impactsprinklers.

Fruit flesh firmness and starch clearing were evaluated usingstandard methods every 5–7 days beginning about 20 days beforeanticipated harvest. To allow for maximum growth, fruit were har-vested when the starch was 80–90% converted, at which time 10apples of approximately the same diameter were removed fromthe east side of each of three middle trees per replication (n = 90).Fruit were taken to the laboratory and stored at 1.1 ◦C until fur-ther examination. Individual fruit were weighed and the number

of lenticels on each apple at the widest part was counted within a20 mm diameter ring on opposite sides of the fruit, perpendicular tothe most exposed side. Lenticel density was calculated by dividingthe number of lenticels by the area within the ring and averaging

92 S.S. Turketti et al. / Scientia Horticulturae 138 (2012) 90–95

Table 1Sampling dates for 2009/10 and 2010/11 for the three different sites.

Phenological phase Vastrap (VAS) Tandfontein (TFT) Nooitgedaght (NGD)

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During this phase in 2010/11 season (data not shown), TFT had anincrease in relative humidity and the temperature remained con-stant. It is possible that these conditions favored cuticle formation

Table 2Average number of lenticels per cm2 from two opposite sides of a ‘Royal Gala’ apple(median) on three different sampling dates (40 dafb, 70 dafb and 100 dafb-harvest)for 2009/10 and 2010/11 seasons. Stage represents the mean developmental phaseof the lenticels, averaged across replicated samples per date. Different letters withinorchards indicate statistically significant differences on a 5% level.

Treatment 40 dafb

2009/10 2010/11

Lenticels (cm2) Stage Lenticels (cm2) Stage

NGD 9.33a 1.5 ns 12.17a 1.0a

VAS 5.42a 1.2 9.92a 1.0TFT 27.80b 1.2 21.58b 1.0

LSD5% 9.24 0.3734 6.208P > F <0.0001 0.5654 0.0013

Treatment 70 dafb

2009/10 2010/11

Lenticels (cm2) Stage Lenticels (cm2) Stage

NGD 7.42a 1.5 ns 8.83 ns 1.3abVAS 7.17a 2.0 6.67 2.2aTFT 16.08b 1.2 8.91 1.2b

LSD5% 4.28 0.1156 4.331 0.0497P > F 0.0002 0.7996 0.4951 0.8407

Treatment Harvest

2009/10 2010/11

Lenticels (cm2) Stage Lenticels (cm2) Stage

NGD 7.08a 2.5 ns 4.08 ns 1.7bVAS 6.42a 2.7 4.67 2.8a

40 dafb 23/11/09 01/12/1070 dafb 22/12/09 05/01/11

100 dafb 27/01/10 11/02/11

his calculation from both sides. Fruit was returned to cold storaget 1.1 ◦C for about five months.

After 150 days at 1.1 ◦C, apples were processed over a small-cale packing line to induce lenticel breakdown similar to theethod described previously (Curry et al., 2008) with minor modi-

cations. First, cold fruit were submerged for 3 min in a water bathept at 33 ◦C, after which they were placed on the packing line andonveyed through a soap wash, cool water rinse, wax treatment,rush polisher and warm air (43.3 ◦C) dryer. Apples were placedn trays in boxes and returned to −1 ◦C for 48 h before record-ng lenticel breakdown values. Lenticel breakdown was assessed byounting the number of discrete, darkened, lenticel-centered pitsithin a 2 cm diameter ring placed over the most severely affected

rea of the fruit. Data are presented as the percentage of fruit withenticel breakdown values >1.

. Results

.1. Lenticel distribution and size in Western Cape, South Africa

.1.1. Using peel imprints to determine number and size ofenticels per cm2

Sampling dates for the three phenological stages for each siteuring the two seasons are summarized in Table 1. For each of theates, the average number of lenticels on 1 cm2 of an apple (on theedian part of two opposite sides of six apples) was counted and

esults are presented in Table 2. The developmental stage of theenticel was also recorded (Table 2).

The number of lenticels analyzed through imprints made frompple skins, show a similar pattern of that found in literature,veraging from 2 to 10 on 1 cm2. The average number of lenticelst harvest on 1 cm2 for all sites during 2010/11 (4.3) was almost0% lower than that calculated in 2009/10 (8.3). The average fruitize of the crop was smaller in 2010/11 compared to the previouseason for all three sites, and is unfortunately not available for theruit used for the actual lenticel measurements. If the average fruitiameter of the sites is accepted as representative of the sampledruit, the hypothetical fruit surface area for each site could be calcu-ated and from that, the hypothetical number of lenticels per fruitalculated for each site at harvest. This indicated that, not only washe fruit smaller during 2010/11, but this lead to substantially lessenticels per fruit, given the assumptions for the calculations, whichs contrary to the principle that lenticel number per cm2 decreasess fruit size increases when fruit expands. At harvest, fruits fromhe 2010 season had approximately half the number of lenticelsompared to fruit from 2009. However these fewer lenticels in 2010ere larger in size and further developed than the lenticels of 2009.

his may have enabled the fruit to respond similarly under com-arable conditions, regarding moisture loss through the lenticels.

During both seasons, TFT had significantly more lenticels perm2 compared to the other two sites at 40 dafb. This trend contin-ed at 70 dafb during 2009/10, but no significant differences werebserved between the sites in 2010/11. Similarly, the significantifferences between TFT and the other sites continued until har-

est 2009/10, but again, this was not found for lenticel numberst harvest 2010/11. TFT showed a significantly higher number ofenticels per fruit compared to the other two sites during 2009/10nd at 40 dafb in 2010/11. The higher number of lenticels found

1/09 14/12/10 25/11/09 10/12/102/09 05/01/11 22/12/09 05/01/111/10 4/03/11 27/01/10 17/02/11

in TFT could be related to climatic conditions at this site. DuringNovember 2009/10 and 2010/11 (approx. 15–45 dafb), TFT max-imum temperatures were higher than those of VAS, which couldhave predisposed the formation of a higher number of lenticels.

According to Curry (2003), climacteric conditions influence therate of fruit expansion and wax development. If rapid climatechanges from cool, cloudy conditions to hot, dry, sunny conditionsoccur, e.g. at microclimate conditions in an orchard or differentexperimental sites, wax development may be delayed because ofeither the influence of excessive incident radiation-induced heatstress, or the inability of the fruit to supply sufficient substratefor wax development. Under these conditions, the underlying cellsmay become exposed to the desiccation pressure of the environ-ment and start to produce suberin along the exposed cell surfaces,leading to openings that may appear as fine white cracks. If theseclimatic conditions remain for an extended period, lenticels areforced to expand and the cuticle may also crack and expose theunprotected cells beneath the cuticle. Between 70 and 100 dafb,the final phase of fruit expansion, the cuticle almost doubles in size.

TFT 11.33b 2.7 4.42 1.7b

LSD5% 3.82 0.8746 4.227 0.0057P > F 0.0269 0.7890 0.9611 0.7452

a No statistical analysis was performed because stages were similar.

S.S. Turketti et al. / Scientia Hortic

Table 3Average length and depth of lenticels from two opposite sides of ‘Royal Gala’ applesas determined with a cross-section of a lenticel on three different sampling dates(40 dafb, 70 dafb and 100 dafb-harvest) for 2009/10 and 2010/11 seasons. Differentletters within orchards indicate statistically significant differences on a 5% level.

Treatment 40 dafb

2009/10 2010/11

Length Depth Length Depth

NGD 337.65b 114.44c 610.26 ns 171.75 nsVAS 440.78a 194.73a 724.33 222.82TFT 477.54a 164.04b 655.33 199.85

P 0.0288 <0.0001 0.2714 0.0277LSD5% 102.62 27.377 133.12 35.96

Treatment 70 dafb

2009/10 2010/11

Length Depth Length Depth

NGD 575.81a 166.84b 654.52 ns 218.02 nsVAS 415.39c 203.08a 757.11 217.85TFT 527.88b 166.33b 707.56 203.14

P <0.0001 <0.0001 0.3354 0.5714LSD5% 41.497 20.963 142.61 33.78

Treatment Harvest

2009/10 2010/11

Length Depth Length Depth

NGD 532.77b 181.44c 1091.52a 242.41bVAS 770.89a 253.49a 667.01b 181.25aTFT 617.06b 218.13b 1168.22a 293.59b

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P 0.0007 0.0018 <0.0001 0.0046LSD5% 104.08 34.512 183.69 60.401

nd wax development and therefore the masking of some lenticelsue to a slower fruit growth rate (Curry, 2005). Based on previoustudies (Curry, 2003, 2005, 2009; Tessmer, 2009) and observationsn the present study, it seemed possible that ‘immature’ lenticelsstomata) at 40 dafb can eventually be covered by the cuticle, result-ng in a lower lenticel number at harvest.

.1.2. Measuring length and depth of lenticels by cross-sectionsTable 3 shows the average size in depth and length of a typical

enticel at the three phenological stages, for both seasons. At 40afb, the length of the lenticels in NGD was significantly smallerhan the other two sites’ length in 2009/10, but the depth of theenticels were all significantly different from one another. At 70afb in 2009/10, the lengths of lenticels in all three sites differedignificantly from one another and the depth of lenticels in VASas significantly bigger than the other sites. At harvest in 2009/10,

he length and depth of the lenticels from VAS were significantlyigger that for the other sites. The lenticel depth varied signif-

cantly between all three sites, with the shallowest in NGD andeepest in VAS. During the following season, no significant differ-nces between sites were noted at 40 and 70 dafb. At harvest, theenticel length and depth in VAS were significantly smaller that forhe other two sites, but the lenticel depth all differed between sites,ith the smallest in VAS and deepest in TFT.

When the size of lenticels was determined through cross-ections, ‘air pockets’ were observed underneath openings in thepidermis. This was noticed mainly at 40 dafb in ‘immature’ and

intermediate’ lenticels. Partial separation of the lenticels from the

urrounding epidermis has been observed previously in ‘Elstar’,Falstaff’, ‘Gala’, ‘Galaxy’, ‘Golden Delicious’ and ‘Pinova’ applesAmiri and Bompeix, 2005; Tessmer, 2009). This phenomenon can

ulturae 138 (2012) 90–95 93

be aggravated by a sudden abundant water supply after a period ofdrought (Curry, 2003).

3.1.3. Lenticel development stagesDuring 2009/10, there were no significant differences between

the sites during the three phenological stages (Table 2). However,there was a shift from a dominant ‘immature’ phase (1) at 40dafb towards a ‘developed’ stage (3) at harvest. Similarly, during2010/11, no significant differences between sites were found at 40dafb, with a dominant ‘immature’ phase. However, at 70 dafb, thedevelopmental stage at VAS was significantly different from that ofTFT, but not from NGD. While VAS showed more cells in the ‘inter-mediate’ stage (2), the other two sites tended to have ‘immature’(1) cells. At harvest, the significant difference between the devel-opmental stages of VAS (2.8) and TFT (1.7) remained, with NGD(1.7) also differing significantly from VAS. At harvest 2010/11, thegeneral stage of development (1.7–2.8) also lagged behind that of2009/10 (2.5–2.7).

Although all three stages of lenticel development, as definedin our study, occurred on the fruit surface throughout the differentdevelopmental fruit phases, ‘immature’ lenticels occurred in highernumbers during the first phase of fruit development (40 dafb) andwere more difficult to observe during the subsequent fruit devel-opmental phases. The ‘developed’ stage was rarely found in thebeginning of fruit development, but became more abundant afterthe fruit reached its final size (70 dafb onwards).

3.2. Temperature data

From the temperature data, growing degree hours during fruitdevelopment were calculated for TFT and VAS, from full bloomto first harvest (data not shown). NGD temperatures were onlyavailable for 2010/11. No obvious trends could be found that coulddescribe the lenticel breakdown sensitive seasons. Maximum dailytemperatures during January and February (data not shown) couldalso not be related to the lenticel breakdown incidence reported in2004/5, 2005/6 (high lenticel breakdown) or 2006/7 (some lenticelbreakdown incidence).

We also examined daily maximum temperature early during theseason, dividing the season into 20 days intervals from full bloomuntil 70 dafb. From approx. 27 to 41 dafb during 2004 and 2005(high lenticel breakdown), maximum hourly temperatures at TFTseemed to be consistently higher than during the years of no or littlelenticel breakdown e.g. 2007 and 2009 (Fig. 2). Although no lenticelbreakdown was found in the samples in either 2009/10 or 2010/11,temperatures during 2008 followed a similar trend to those of 2004and 2005 (data not shown). Fig. 3 shows the temperatures above20 ◦C between approx. 15 and 45 dafb for both seasons and indicateshigher temperatures occurring at TFT compared to VAS. This maypartly explain the higher number of lenticels found at 40 dafb forboth seasons in TFT compared to VAS. In Fig. 4, the number of dayswith a relative humidity lower than 40% (stress conditions), showsdata only for TFT, indicating that these conditions did not occur atVAS during December 2009/10–2010/11, corresponding to 40–70dafb.

3.3. Lenticel density and lenticel breakdown in ‘Gala’ sports inWashington State, USA

There was no difference in fruit maturity among the four ‘Gala’sports according to measurements of starch clearing index and fruitflesh firmness (data not shown). On the other hand, there were

down. There was a highly correlated inverse relationship (Pearsoncorrelation coefficient = −0.91) between lenticel and percent lenti-cel breakdown (Fig. 5). ‘Brookfield’ had the lowest lenticel density

94 S.S. Turketti et al. / Scientia Horticulturae 138 (2012) 90–95

10

15

20

25

30

352

0

27

34

41

Te

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35

20

27

34

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Te

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Fig. 2. Average maximum hourly temperatures from 20 to 47 dafb for the Tand-fontein (TFT) weather station from 2004 (04TFT) to 2010 (07TFT, 09TFT, 10TFT).(A) Years with lenticel breakdown incidence (2004, 2005, 2006) versus no lenticelbreakdown (2008) and (B) lenticel breakdown (2004) versus no lenticel breakdown(2007, 2009, 2010).

20

22

24

26

28

30

32

34

30221581

Te

mp

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°C

November

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10TFT

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10

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2

whereas lenticel density is the number of lenticels per cm peel surface area. Barsindicate + SE.

and highest percent lenticel breakdown, whereas the reverse wastrue for ‘UltraRed’.

Pooled data indicated no significant correlation between lenticeldensity and fruit weight (Fig. 6). However, correlation coefficientsfor ‘Brookfield’, ‘Pacific’, ‘Royal’ and ‘UltraRed’ were 0.42, 0.13,−0.13, and −0.24, respectively. That is, the direction of correla-tions, i.e., the correlation moments, varied from positive to negativewith increasing lenticel density. Although this is a preliminary find-ing and correlation coefficients are weak, data may indicate that‘Gala’ sports with a higher propensity for developing lenticel break-down show increased incidence as fruit weight (size) increases,whereas sports with a lower propensity to develop lenticel break-down do not. This may indicate susceptible fruit are less able torepair cracking of the lenticular annulus. Further research is needed

to substantiate this possibility.

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Fruit weight (g)220 280200 240180

Correla�on coefficient = -0.04

4

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Fig. 6. Lenticel density as a function of fruit weight for all ‘Gala’ sports sampled fromWashington in 2009. Straight line indicates direction of the correlation coefficientwhereas ellipse is centered on the sample means of the x and y variables (P < 0.95).

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. Discussion

Lenticel breakdown has been associated with a variety of factorshat range from pre-harvest cultural practices to storage man-gement, including ambient conditions. This study examined theossibility that lenticel breakdown might be related to ‘Gala’ strain,

enticel size and phenological stage. Results from Ceres revealedhat environmentally different cultivation sites presented fruit withignificant differences in number of lenticels. The highest incidencef lenticel breakdown was reported in Tandfontein after a year2004/05) where the average maximum temperatures throughouthe year were extreme compared to the other sites.

Although no lenticel breakdown was observed during the twoeasons investigated, Tandfontein had a higher number of lenticelsf larger sizes. Relative humidity at Tandfontein and Nooitgedaghtas lower (Ave.: 52.0%) in comparison to Vastrap (Ave.: 77.1%) from

ull bloom to harvest during the two evaluation seasons and was fol-owed by a constant number and size of lenticels. We believe thatlimate information, such as temperature and relative humidity,re important observations during fruit development as indicatorsor post-harvest management, and can enable early predictions ofossible lenticel breakdown allowing for preventative measure-ents.The evaluation of lenticel size, including imprints and cross-

ections, did not present any distinct pattern and therefore weould not establish a relationship between lenticel size and lenti-el breakdown incidence. In contrast, the developmental stage ofhe lenticels revealed a distinct pattern that followed the fruitevelopmental stages. While some authors denominate the ‘imma-ure’ lenticels as stomata, maintaining the principle proposed bylements (1935), we described a lenticel as any opening in the cuti-le providing it has the shape of the stomata or resembles a crack inhe cuticle. In addition, our analysis indentified ‘air pockets’ under-eath the lenticel regions that may contribute to the occurrencef lenticel breakdown in apples. How the ‘air pockets’ originatend their possible influence in lenticel breakdown still needs toe confirmed.

From the study in Washington State, a highly correlated inverseelationship between lenticel and percent lenticel breakdown wasstablished. No significant correlation between lenticel density andruit weight was found. This may indicate susceptible fruit are lessble to repair cracking of the lenticular annulus. Further researchs needed to substantiate this possibility.

. Conclusion

The study of lenticel morphology indicated that relativeumidity and temperature can play an important role in lenticel

reakdown due to their influence on the rate of fruit growthnd cuticle development, both related to fruit development.nvironmental conditions at fruit development should be takennto consideration when planning for future studies. Factors that

ulturae 138 (2012) 90–95 95

influence cuticle development, mainly at the final stages of fruitgrowth, should also be investigated. Finally, these studies shouldbe repeated often in orchards where lenticel breakdown incidenceis consistent to substantiate conclusions. Climate change predic-tions in the Cape Floristic Region of South Africa involve 0.5–1.0 ◦Cincrease in temperature and 25% decrease in annual rainfall(Rutherford et al., 1999). This will result in wider variations oftemperature and humidity than observed nowadays and thereforea higher incidence of skin disorders.

Acknowledgements

In South Africa, we wish to thank Mrs. P. Conradie and DuToitAgri for supplying the fruit and historical information in Ceres, aswell as Fruitgro Services and the National Research Foundation whofunded the research.

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