Effect of protected cultivation on the precocity,

yield and fruit quality in loquat

A. Aytekin Polat*, C. Durgac, O. Caliskan

Department of Horticulture, Faculty of Agriculture, University of Mustafa Kemal,

Tayfur Sokmen Kampusu, 31034 Antakya-Hatay, Turkey

Received 12 August 2003; received in revised form 19 February 2004; accepted 23 August 2004

Abstract

The advantages of the high density and protected cultivation over open field were investigated in

three loquat cultivars. Both of these methods are new and have not been previously studied in Turkey.

The study was conducted with Gold Nugget, Hafif Cukurgobek, and Sayda cultivars planted at high-

density with planting spaces of 3 m � 3 m in May 1997. The experiments for cultivation were done in

greenhouses where the side height was 2.5 m and the highest point was 4.0 m. Phenological variables

such as first blossoming, full bloom, end of bloom and harvest time and pomological variables such as

fruit and seed weight, fruit dimension, seed number/fruit, and acidity were determined. The trunk

diameter, 10 cm above the bud union, was also recorded each year during the study. The total above

ground tree canopy volume was calculated from height and width measurements. The productivity

parameters including yield/plant, yield/hectare, cumulative production/plant, cumulative production/

hectare and yield/unit trunk cross-sectional area and yield/unit of canopy volume were calculated.

The results indicated that protected cultivation caused earliness of 13–20 days when compared to

open field. The mean yield was higher in protected cultivation than the open field for both yield/tree

and yield/ha. Conversely, the mean yield was higher in open field than protected cultivation for yield/

unit trunk cross-sectional area and yield/unit of canopy volume of trees. Pomological quality of the

fruits was higher in the open field than protected cultivation.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Eriobotrya japonica; Loquat; Protected cultivation; Pomology; Phenology

www.elsevier.com/locate/scihorti

Scientia Horticulturae 104 (2005) 189–198

* Corresponding author. Tel.: +90 326 245 56 05; fax: +90 326 245 58 32.

E-mail address: apolat@mku.edu.tr (A.A. Polat), cdurgac@mku.edu.tr (C. Durgac),

ocaliskan@mku.edu.tr (O. Caliskan).

0304-4238/$ – see front matter # 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.scienta.2004.08.010

1. Introduction

Enabling higher yield in a shorter time when compared to standard cultivation, high-

density cultivation is getting more popular in fruit production. This method has encouraged

dwarfing the trees by different applications and developing of dwarf trees under protected

cultivation. The advantages of such systems include easier cultivation (e.g., irrigation,

weed control, pest management, harvest), decrease in yield lost by ecological factors,

possibility of working in all weather conditions, increase in marketable fruits, consistent

high yield, and most importantly, earliness and higher profitability (Fideghelli, 1990;

Furukawa et al., 1990).

In Japan, protected cultivation was initiated to compete with fruit import during out of

harvesting period as improving the fruit quality (Iwagaki, 1990). In 1986, Japan had

8514 ha protected area for agriculture of which 803 ha for Satsuma cultivation, 546 ha for

other Citrus species and 64 ha for loquat. The increase in the last 10 years was 16% and 3.6-

fold in area. It is expected that this trend will continue in the future (Kamota, 1988).

In Italy, the protected culture was established as the fruit import from South Africa has

increased during 1960s and now becomes a common technique as it increases the earliness

(De Salvador and Monastra, 1990).

High-density planting is a way to get high yield in short time. The increase in area and

labor cost, easier harvest and pest management, and high yield in short time for high profit

can be listed for the reasons for approaching to high-density planting (Cary, 1981;

Tasdemir and Kaynak, 1992).

In a research conducted in Turkey (Polat, 1990) an earliness of 30–40 days was observed

when containerized trees were carried to greenhouses after the flowering. Although 97% of

loquat cultivation in Turkey was done in Mediterranean Region, there is no detailed study

on high density or protected cultivation. It was our objective to investigate the possibility of

25–30 days earliness by high density and/or protected cultivation.

2. Material and methods

The experiment was established at Faculty of Agriculture Research Station, Mustafa

Kemal University, in 1997. Gold Nugget, Hafif Cukurgobek, and Sayda cultivars were

planted at high-density with planting spaces of 3 m � 3 m in May 1997. The experimental

design was split-plot with cultivation treatment as main-plot and cultivars as sub-plot (Steel

and Torrie, 1980). The protected cultivation was conducted with greenhouses where the

side height was 2.5 m and the highest point was 4.0 m without heated and with drip

irrigation system. The coverage was made by 300 m-thick UV + IR PE. The plastic was

covered from leafbreak to ripening and was removed after harvest. During this period, the

ventilation of the greenhouse was carried out naturally depending on the weather condition.

On cold days, the plastic cover and doors were kept closed to prevent heat loss while on

sunny and hot days, the plastic cover of both long sides of the greenhouse and doors were

kept open from approximately 10:00 am to 15:00 pm.

Phenological variables such as determination of fruit buds, flowering and harvesting

dates were collected from each tree. For pomological variables, such as fruit and seed

A.A. Polat et al. / Scientia Horticulturae 104 (2005) 189–198190

weight, fruit dimension, seed number/fruit, TSS and acidity, five trees were randomly

selected for each treatment and cultivars. Ten fruit from each tree were randomly picked

and analyzed. The yield was determined for both tree and area-basis in the experiment. The

trunk diameter, 10 cm above the bud union, was also recorded in January each year during

the study. This has made possible to conjunctive evaluation of correlation between

vegetative growth and productivity (the variables of yield/unit trunk cross-sectional area

and yield/unit of canopy volume of trees).

The data were analyzed by ANOVA with split-plot design and the mean comparison

with Tukey test.

3. Results

3.1. Flowering and harvest date variables

The averaged 3 years results indicated that the differences in earliness among cultivars

ranged from 1–6 days in protected cultivation and 6–17 days in open field (control) (Fig. 1).

Sayda, which started flowering in full at the start of December was earlier than the other

two cultivars. Full blossoming was 1–12 days earlier in protected cultivation than open

field.

The differences among cultivars in harvest dates ranged from 1–15 in protected

cultivation and 2–7 days in open field. Hafif Cukurgobek was the earliest and Gold Nugget

was the latest cultivars in both protected cultivation and open field (Fig. 2).

The cultivation system was significant for harvest period for the cultivars. In general,

protected cultivation showed 13–20 days earliness when compared to open field (Fig. 2).

A.A. Polat et al. / Scientia Horticulturae 104 (2005) 189–198 191

Fig. 1. Phenological observations of the cultivars from 1999–2002 years.

3.2. Productivity variables

The data from 2000–2002 indicated that average yield was higher in protected

cultivation than the open field for both yield/tree and yield/ha (Table 1). The differences

among cultivation system were statistically significant at 1% level.

The differences in yield among cultivars were also significant at 1% level. Hafif

Cukurgobek and Sayda had higher yield than Gold Nugget for both yield/tree and yield/ha

(Table 1).

The mean yield was higher in open field than protected cultivation for yield/unit trunk

cross-sectional area and yield/unit of canopy volume of trees. The difference was not

significant for yield/unit trunk cross-sectional area; however, significant for yield/unit of

canopy volume of trees (Table 1).

Gold Nugget was the highest yielding and Sayda was the lowest yielding cultivars

for both yield/unit trunk cross-sectional area and yield/unit of canopy volume of trees

(Table 1).

3.3. Cumulative yield

The differences between cultivation systems for the cumulative yield were presented in

Table 1.

As it can be seen from Table 1, protected cultivation had higher yield for cumulative

yield/tree and cumulative yield/ha for consecutive 3 years. However, open field had higher

yields for both cumulative yield/unit trunk cross-sectional area and cumulative yield/unit

of canopy volume of trees. The differences between cultivation systems for these

cumulative yield variables were significant at 1%.

The differences among cultivars for cumulative yield variables were significant at 1%.

Hafif Cukurgobek had the highest and Gold Nugget and the lowest yields for both

cumulative yield/tree and cumulative yield/ha. Gold Nugget had the highest and Sayda had

the lowest yields for cumulative yield/unit trunk cross-sectional area and cumulative yield/

unit of canopy volume of trees.

A.A. Polat et al. / Scientia Horticulturae 104 (2005) 189–198192

Fig. 2. Harvesting period of the cultivars from 1999–2002 years.

A.A

.P

ola

tet

al./S

cientia

Ho

rticultu

rae

10

4(2

00

5)

18

9–

19

81

93

Table 1

Yield/tree, yield/ha, yield/unit of canopy volume of trees and yield/unit trunk cross-sectional area of the cultivars grown under greenhouse and open field conditions

(average of years 2000–2002 and 3-year cumulative)

Cultivation system

and cv.

Average Cumulative

Yield per tree

(kg/tree)

Yield per

area (kg/ha)

Yield per

tree canopy

(kg/m3)

Yield per trunk

cross-sectional

area (kg/cm2)

Yield per

tree (kg/tree)

Yield per

area (kg/ha)

Yield per

tree canopy

(kg/m3)

Yield per trunk

cross sectional

area (kg/cm2)

Greenhouse (Gh)

HCG 9.28 aba 10310 ab 1.66 bc 0.24 ab 27.85 ab 30940 ab 4.98 bc 0.73 ab

Sayda 10.04 ab 11160 ab 1.11 d 0.18 b 30.13 ab 33470 ab 3.32 d 0.55 c

Gold Nugget 10.02 ab 11130 ab 1.49 c 0.24 ab 30.05 ab 33390 ab 4.48 c 0.73 ab

Open field (Of)

HCG 10.57 a 11740 a 1.85 bc 0.24 ab 31.71 a 35230 a 5.59 b 0.73 ab

Sayda 8.59 b 9540 b 1.86 b 0.21 ab 25.76 b 28620 b 5.58 b 0.63 bc

Gold Nugget 5.99 c 6650 c 2.55 a 0.28 a 17.96 c 19950 c 7.64 a 0.84 a

Av. system

Gh 9.78 aa 10870 a 1.42 b 0.22 29.34 a 32600 a 4.26 b 0.67 b

Of 8.38 b 9311 b 2.09 a 0.24 25.14 b 27930 b 6.27 a 0.73 a

Av. cv.

HCG 9.93 aa 11030 a 1.75 bc 0.24 ab 29.78 a 33080 a 5.28 b 0.73 a

Sayda 9.32 a 10350 a 1.48 c 0.20 b 27.94 a 31050 a 4.45 c 0.59 b

GN 8.00 b 8891 b 2.02 a 0.26 a 24.00 b 26670 b 6.06 a 0.79 a

D(system) 1%: 1.12 1%: 1239 1%: 0.22 NSb 1%: 3.35 1%: 3719 1%: 0.65 1%: 0.04

D(Av. cv.) 1%: 1.07 1%: 1190 1%: 0.22 1%: 0.05 1%: 3.22 1%: 3570 1%: 0.65 1%: 0.08

D(system � cv) 1%: 1.81 1%: 2014 1%: 0.36 1%: 0.08 1%: 5.44 1%: 6040 1%: 1.09 1%: 0.14

a Means followed by different letters for each of average system, Av cv. and system � cv., are significantly different at 1% by Tukey test.b Not significant.

3.4. Pomological variables

3.4.1. Fruit and seed weight

The cultivation system was significant for fruit and seed weight variables at 1%

significance level. Both of these weights were higher in open field than protected

cultivation (Table 2).

Hafif Cukurgobek had higher values than the other two cultivars for both fruit and seed

weight. However, these differences were found to be significant at 1% level when

compared to those of Gold Nugget.

3.4.2. Fruit height and width

The fruit height and width was higher in open field than protected cultivation. The

difference between cultivation systems was significant at 1% level.

The fruit width was the highest in Hafif Cukurgobek and fruit height was the highest in

Sayda (Table 2).

3.4.3. Seed number and flesh/seed ratio

The both seed number and flesh/seed ratio was higher in protected cultivation than open

field. However, this difference between cultivation systems was not statistically significant

(Table 2).

The differences among cultivars for seed number and flesh/seed ratio were significant at

5% level. Hafif Cukurgobek had the highest seed number while Gold Nugget had the

lowest. Flesh/seed ratio was the highest in Gold Nugget and the lowest in Sayda.

3.4.4. Soluble solids, pH, and acidity

Protected cultivation had lower values for soluble solids and acidity, and higher values

for pH than open field. These differences between cultivation systems were significant for

soluble solids and pH, but not significant for acidity (Table 2).

The differences among cultivars for soluble solids, pH, and acidity were found to be

significant at 1%. Sayda had highest values for soluble solids and acidity and Gold Nugget

had the highest value for pH.

4. Discussion

Loquat is an important fruit to fulfill the fresh fruit needs in spring as it matures in April

and May. It is possible to increase yield and quality if cultivation of this species can

extensively be studied on dwarf rootstocks and protected systems (Polat, 1996). These

systems are getting more popular in Turkey and in the world. Takase et al. (1988) reported

that protected and heated cultivation of loquat induced 37–76 days of earliness when

compared with the open field. High-density planting is a way to get high yield in short time.

The various investigators indicated that it is possible to increase yield by high-density and

utilizing dwarf rootstock. From this point, the investigation of possible usage of quince as a

dwarfing rootstock for loquat gave promising results (Polat and Kaska, 1992a, 1992b;

Polat, 1995).

A.A. Polat et al. / Scientia Horticulturae 104 (2005) 189–198194

A.A

.P

ola

tet

al./S

cientia

Ho

rticultu

rae

10

4(2

00

5)

18

9–

19

81

95

Table 2

Some pomological characteristics of the cultivars grown under greenhouse and open field conditions (average of years 2000–2002)

Cultivation system

and cv.

Fruit

weight (g)

Seed

weight (g)

Fruit

width (mm)

Fruit

height (mm)

Seed

number

Flesh/seed

ratio

TSS (%) pH Acidity (%)

Greenhouse(Gr)

HCG 23.56 cda 5.03 b 33.24 bc 37.26 bcd 4.61 a 3.72 a 8.97 b 3.74 a 0.40 c

Sayda 23.21 cd 4.97 b 32.18 bc 39.00 bc 4.02 ab 3.70 a 10.28 b 3.42 bc 0.71 a

Gold Nugget 20.51 d 4.45 b 31.18 c 33.76 d 4.20 a 3.70 a 9.97 b 3.59 ab 0.43 bc

Open field (Of)

HCG 33.84 a 7.73 a 36.79 a 40.74 ab 4.01 ab 3.43 ab 9.59 b 3.29 c 0.63 ab

Sayda 28.66 b 7.29 a 34.16 b 43.50 a 4.11 ab 2.98 b 12.32 a 3.30 c 0.75 a

Gold Nugget 26.40 bc 5.64 b 33.43 b 35.84 cd 3.53 b 3.86 a 9.75 b 3.47 bc 0.56 abc

Av. system

Gh 22.43 ba 4.81 b 32.20 b 36.67 b 4.28 3.70 9.74 b 3.58 a 0.51

Of 29.63 a 6.89 a 34.79 a 40.03 a 3.88 3.43 10.55 a 3.35 b 0.65

Av. cv.

HCG 28.70 aa 6.38 a 35.01 a 39.00 a 4.31 a 3.58 ab 9.28 b 3.51 a 0.52 b

Sayda 25.93 ab 6.13 a 33.17 b 41.25 a 4.06 ab 3.34 b 11.30 a 3.36 b 0.73 a

GN 23.46 b 5.05 b 32.31 b 34.80 b 3.86 b 3.78 a 9.86 b 3.53 a 0.50 b

D(system) 1%: 4.36 1%: 1.06 1%: 1.68 1%: 1.89 NSb NS 5%: 0.63 5%: 0.15 NS

D(Av. cv.) 1%: 2.85 1%: 0.75 1%: 1.28 1%: 2.33 5%: 0.37 5%: 0.37 1%: 1.02 1%: 0.13 1%: 0.13

D(system � cv) 1%: 4.69 1%: 1.23 1%: 2.12 1%: 3.84 5%: 0.64 5%: 0.65 1%: 1.68 1%: 0.22 1%: 0.21

a Means followed by different letters for each of average system, Av cv. and system � cv., are significantly different at 1% or 5% by Tukey test.b Not significant.

The present loquat orchards were established as classical production system of 6 m �6 m, 7 m � 7 m, and 8 m � 8 m planting density. In this way, until the full yield potential

reached, 10–12 year, the open field cannot be used efficiently. For this reason, high and

semi high-density cultivation systems can be valuable in loquats as it is the case in other

fruit species, as they increase the yield. Moreover, protected cultivation can result in 25–30

days of earliness. There is no previous study in our country that investigated high-density

and protected cultivation. Although it was initiated relatively recently, other countries are

working rigorously in this area. When all of these considered, the promising results were

obtained in our study where we (a) studied the advantages of high density cultivation over

the classical cultivation, (b) investigated the earliness level of protected cultivation

especially on high density planting, (c) elucidated the difference in fruit quality factors

between our and classical systems.

The cultivation system was significant for harvest period for the cultivars. In general,

protected cultivation showed 13–20 days earliness when compared to open field (Fig. 2).

These results are better than the results of Lorente et al. (2003). Because, Lorente et al.

(2003) reported that cultivation in a greenhouse with a plastic covering resulted in earlier

harvesting in Algerie cv. by 10–12 days and Redonet cv. by 6 days, in Alicante, Spain.

The data from 2000–2002 indicated that average yield was higher in protected

cultivation than the open field for both in terms of yield/tree and yield/ha (Table 1). The

differences among cultivation system were statistically significant at 1% level. The mean

yield was higher in open field than protected cultivation for yield/unit trunk cross-sectional

area and yield/unit of canopy volume of trees. The difference was not significant for yield/

unit trunk cross-sectional area; however, significant for yield/unit of canopy volume of

trees (Table 1). This means that the trees became bigger than the trees in open field.

However, this problem can be solved by using dwarf rootstocks such as Quince-A and BA-

29. Moreover, Quince-A rootstock has 25% of dwarfing effect than loquat seedling

rootstock (Polat, 1995). In addition, it is also possible to use growth regulators such as

pacroputrazole to dwarf the trees. In this study, the grow rates of the trees were kept under

control by pruning. In this case, by high-density cultivation under protected cultivation, it is

possible to benefit economically from the use of loquat for 10–12 years.

Both of fruit and seed weights were higher in open field than protected cultivation and

also, the fruit height and width was higher in open field than protected cultivation (Table 2).

These results were in consistent with the results of Takase et al. (1988) and Lin et al.

(1999). Takase et al. (1988) reported that an increase in night temperatures of greenhouse

caused a decrease in the fruit diameter. Moreover, Lin et al. (1999) reported that higher

temperatures accelerated the growth of young fruitlets but increased fruit maturation,

which resulted in small fruit.

Protected cultivation had lower values for soluble solids and acidity, and higher values

for pH than open field. These differences between cultivation systems were significant for

soluble solids and pH, but not significant for acidity (Table 2).

We can say that the fruits from the trees under protected cultivation are smaller and have

less TSS but these results are not of very importance for protected cultivation. Because, in

Turkey, precocity is more profitable than conventional cultivation. Therefore, reduction in

fruit quality to some extent when grown under protective cultivation does not appear to

affect this situation. Reduction in total soluble solid in early ripening fruits under protected

A.A. Polat et al. / Scientia Horticulturae 104 (2005) 189–198196

cultivation does not hinder their production and marketing. Marketing time is more

important than some quality criteria of the fruit. Protected cultivation proved to be

profitable due to higher prices from earlier marketing.

It was not possible to compare our results to literature from Turkey and other countries

as there have been no previous studies reported; however, it is possible to conclude that

protected cultivation can result in 15–20 days of earliness and also help reach full yield

potential in shorter time. Also, depending on cultivars, earliness can be extended to 30

days. Moreover, high-density cultivation system can be utilized in near future and it may

increase the yield per area three to four fold (Polat et al., 2002). Therefore, nurseries should

initiate producing loquat trees on quince rootstock.

As a result, the research should be continued to determine the mutual effect of high-

density and protected cultivation using dwarf rootstock.

Acknowledgement

This research was supported by a grant from the Scientific and Technical Research

Council of Turkey (contract no: TOGTAG/TARP-2336).

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