Effects of Aminoethoxyvinylglycine on Harvest Time and Fruit Quality of ‘

This study was conducted to prolong the harvest date and enhance the fruit quality of ‘Monroe’ peaches. For this purpose, ReTain containing 15% aminoethoxyvinylglycine (AVG) was applied to the peach fruits. AVG at concentrations of 0, 100, 150 and 200 mg l was sprayed on the peaches 7, 21 and 30 days before commercial harvest. Some fruit quality parameters [fruit weight (g), fruit flesh firmness (N), soluble solids content (SSC, %), titratable acidity (TA, %), fruit colour (L*, a*, b*), sugar content, delay in harvest, ethylene production (μl kg h) and respiration rate (ml CO2 kg h)] were measured for each treatment. Fruit maturity was delayed about 4-6 days more in AVG-applied fruits than in the control group. A sequential harvest was completed 6-7 days before the normal harvest time. Application of AVG increased the fruit size and fruit weight of ‘Monroe’ peach. AVGsprayed fruits were firmer than the fruits of control group. AVG applications also decreased ethylene production and the respiration rate of fruits. As a results, application AVG of 100 or 200 mg l concentrations 30 days before commercial harvest for 'Monroe' peach varieties can be recommended.


Introduction
Ethylene is a highly potent plant hormone that is intimately involved in basic plant processes such as seed germination, seedling development, flowering, fruit development, abscission, disease resistance and senescence (Kaşka & Yılmaz 1974;Hartmann 1997;Curry 1998;Rath & Prentice 2004).
1-aminocyclopropane-1-carboxylase (ACC) synthase catalyses 1-aminocyclopropane-1-carboxylic acid (ACC) and it is converted to ethylene by ACC oxidase (ACO) (McGlasson et al. 2005).Aminoethoxyvinylglycine (AVG) is a potent inhibitor of ACC synthase in the ethylene biosynthesis pathway (Boller et al 1979;Kim et al 2004) and can thus suppress ethylene production in many climacteric fruits (Yang et al 1982).ReTain ® Plant Growth Regulator, containing 15% w w -1 AVG, was registered in Australia in October 2001 for use with apples, peaches and nectarines (Rath & Prentice 2004).Pre-harvest spraying with ReTain ® has been demonstrated to delay ripening and reduce pre-harvest drop of fruits in apples, peaches, nectarines and other climacteric fruits (Autio & Bramlage 1982;Park et al 1999;Bregoli et al 2002).However, the effects of AVG depend on application concentration and time cultivar and environmental conditions (Matoo et al 1977;Kim et al 2004).Furthermore, AVG is known to be less effective in inhibiting ethylene biosynthesis at lower temperatures (Bramlage et al 1980).
Fruit softening is known to be one of the ripening processes that are most sensitive to ethylene.Fruit softening in peaches is correlated with an increase in ACC and ethylene production.AVG applied as a pre-harvest spray to peaches delays maturation (Rath & Prentice 2004).ReTain ® applied 15, 10 or 5 days before the commercial harvest of late maturing peaches cultivars ('O'Henry', 'Summerset') delayed fruit maturity on the tree and delayed harvest.The application of ReTain ® at 5-10 days before harvest has shown to be more effective in improving fruit firmness and quality of late maturing cultivars of peach than application at 15 days before harvest.
Noppakoonwong et al (2005) found that AVG applied to 'Tropic Beauty' peach prior to harvest significantly increased fruit size, firmness and sugar concentration.Another study by Kim et al (2004a) showed the effect of various concentrations (100, 150, 200 mg l -1 ) of AVG sprayed onto 'Mibaekdo' peach trees at 3 and 4 weeks before the commercial harvest date.AVG spraying greatly reduced the pre-harvest fruit drop rate in a concentration-dependent manner.AVG sprayed at 3 weeks before commercial harvest date appeared to be more effective than at 4 weeks before the commercial harvest date.At harvest, the AVG-sprayed fruits had significantly higher weight than control fruits.They also decreased ethylene production and respiration rate.
This study was conducted in Isparta, where is one of the most important production centers for peaches in Turkey.Poor fruit quality leads to serious problems in the marketing of fruits in this area.This problem also causes significant losses in peach cultivation in Turkey.This study examining fruit quality characteristics such as weight, firmness and colour and criteria such as delaying harvest time, reducing the harvest levels and including issues of provision, is one of the first studies of its type in a Turkish context.
In this study, it was examined that effects of pre-harvest application of ReTain ® on harvest delay, fruit size, fruit quality, ethylene production, respiration rate, sugars and some leaf properties of 'Monroe' peach.

Materials and Methods
Experiments were conducted in commercial peach orchards located in Isparta, at an altitude of 963 m -971 m asl.Uniform trees, 14-years-old cv.'Monroe' peach on P. persica rootstock, spaced at 6x5 m were used.Trees were trained into a vase system and pruned in late winter, and standard cultural practices including thinning and pesticide sprays had been used with the trees for several years.The experimental design was a randomized block, with 12 treatments and 5 replicates using a single tree for each treatment.ReTain ® containing 15% AVG, obtained from Valent BioSciences Corp., USA, was sprayed at concentrations of 0 (water+surfactant), 100, 150, 200 mg l -1 AVG plus 1% (v/v) Tween 20 as a surfactant onto fruits and leaves around the fruits until runoff.The spraying was performed with a hand pump sprayer at 7, 21 and 30 days before commercial harvest (DBH) in the first and second years.Fruits were harvested at a commercial stage of maturity when the ground colour changed from green to yellow-red at intervals of 3-4 days for yield and fruit assessment.ReTain-treated fruits and untreated fruits were harvested separately and picked bins.After each harvest, the fruit was transported 30 km to the Postharvest Physiology Laboratory of Horticulture Department where the fruits were placed into cold storage (1°C) until the analyses were performed.
Fruits were harvested 3 times from 28 August to 8 September 2007 (in the first year) and 26 August to 3 September 2008 (in the second year).The data used for analysis in this paper comes from the second harvest because the percentage of commercial mature fruit picked was seen in the second harvest.The fruit weight, fruit colour (measured with a Minolta Chroma Meter CR-300 using the CIE L*, a* and b*), colour space, fruit firmness (using a Lloyd LF Plus Universal Test Machine), and soluble solids content (SSC) (using a digital Palette PR-32 Atago refractometer) were measured.The colour was measured on both sides of the fruit to determine its ground colour and the red exposed area.Therefore, four measurements were done for each fruit.Fruit firmness was tested at two points on the fruit surface with a plunger of 8 mm diameter.Titratable acidity (TA) was determined using a digital buret (Digitrate Isolab 50 ml) by titration with 0.1 N NaOH up to pH 8.1, using 10 ml of diluted juice, and the TA was expressed as malic acid.Ethylene production (µl kg -1 h -1 ) and respiration rate (mL CO 2 kg -1 h -1 ) were determined for peaches of close to the jar after 1 day at room temperature (20±1 °C) (1 kg of fruit was closed in each jar and the volume of each jar was 4 litres).The measurement of the respiratory rate was done with a gas analyser.The ethylene production rate was determined using gas chromatography with a flame ionization detector.(Gunes et al 2001) To determine the total sugars (%), a modified Anthrone method (Sanz et al 1987) was used.Reducing sugar contents (%) were determined using the dinitrophenol method.This method is a modification of the colorimetric method used by Ross (1959).Reducing sugars were extracted by water and reacted with dinitrophenol solution.The changes in absorbance were measured at 600 nm.Moreover, the leaf area index and the chlorophyll content were determined for twenty leaves showing average growth from the upper, middle, and lower parts of the outer canopy.The leaf area index (LAI) was measured by leaf area meter (AM 300 Area Meter, ADC, BioScientific Ltd.) (Ünlü 2000;Kim et al 2004b).Chlorophyll was extracted with 80% acetone, and measured using a spectrophotometer (UV-1601, Shimadzu, Japan) at 645 and 663 nm.The experiment was conducted in 3 (application time; 30, 21 or 7 d before of harvesting)  4 (AVG concentration; 0, 100, 150 or 200 mg l -1 )  2 (years; first and second) factorial arrangements with completely randomized block design.Each treatment had five replications of 20 peaches.Statistical analyses were performed with General 180 Linear Model using SPSS (V.16; Statistical software, SPSS.Inc., USA).Mean separation was performed using Duncan's multiple range test at P<0.05 level.

Fruit maturity and harvest time
Effects of AVG concentrations and its application time on fruit weight and fruit firmness were given in Table 1.AVG applications delayed the development of the background colour of 'Monroe' peaches.As a result, AVG-treated fruits were harvested later than control fruits.Fruit maturity was delayed about 4-6 days in AVGapplied fruits.While the control group was harvested 3 times, AVG-treated fruits were harvested twice (in the first and second year).A sequential harvest was completed 6-7 days before the normal harvest time.Our data was in agreement with previous reports on AVG treatments (Ju et al 1999;Sing et al 2003;Rath & Prentice 2004;McGlasson et al 2005;Noppakoonwong et al 2005).AVG treatments had effects on the percentage of commercial mature fruit at each harvesting date.

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AVG applications increased the percentage of mature peaches compared to the control fruits (2 nd and 3 th harvest date).In 3 September of second year, the interaction between concentration and application time for mature fruit were found statistically significant (P<0.01).The effects of AVG concentrations were statistically significant (in the first year-28 August (P<0.001),3 September (P<0.01), 8 September (P<0.01) and second year 26 August (P<0.001),30 August (P<0.01)).The highest percentage of commercial mature peaches was found with 30 DBH-200 mg l -1 (in the first year) and 7 DBH-200 mg l -1 (in the second year) AVG treatments (P<0.05).

Fruit quality
Fruit weight and fruit firmness: Effects of AVG concentrations and its application time on fruit weight and fruit firmness were given in Table 2. AVG applications had generally positive effects on the fruit weights.In first year, the interaction effects between AVG concentrations and application times on the fruit weight were found statistically significant (P<0.05).In this year, the highest fruit weight was obtained from 100 mg L -1 AVG concentration at 30 DBH.In the second year, the main effect of AVG concentrations on fruit weight was statistically significant (P<0.001) and fruits treated with 200 mg l -1 AVG concentrations were heavier than the other groups.

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The effects of all the application times and concentrations are quite prominent.The findings on fruit weights in our study are similar to those of Kim et al (2004a), Rath et al (2004), Rath & Prentice (2004) and Amarante et al (2005).
AVG had significant effects (P<0.001) on fruit firmness only for second year (Table 2).All AVG concentrations had higher fruit firmness values than control group.In the first year, the main effect of AVG application times was statistically significant (P<0.05).In this year, the highest fruit firmness (44.70 N) was found with 30 DBH-100 mg l -1 AVG treatment.Like our findings, Rath et al ( 2004) also reported that application 83-125 mg l -1 AVG to 'Tatura 204', 'Golden Queen' and 'Taylor Queen' peaches resulted in a reduction 7-14 days of harvesting time with increasing fruit firmness by 7-58% compared to control fruits.
Fruit colour: Effects of AVG concentrations and its application time on fruit colour were given in Table 3.In the both years, interaction effects of AVG concentrations and application times on the fruit colour L* values (bright colour) were statistically significant (P<0.05).The highest L* value was 53.08 with 7 DBH-150 mg l -1 , while the lowest L* value was 43.08 with 7 DBH-100 mg l -1 in the first year.In the second year, the 21 DBHcontrol fruits had the highest L* values.AVG a-c : Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05) concentrations on fruit colour a* values (green to red colour development) were statistically significant (P<0.05) in the first year (Table 3).The best concentration was 200 mg l -1 for application times.In the second year, the interaction between concentrations and times on the fruit colour a* values were statistically significant (P<0.05) with AVG-treated fruits having better a* values than the control group.In the first year, the interaction between concentrations and times on the fruit colour b* values (yellow ground colour) were significant (P<0.01).The control fruits and 21 DBH-100 mg l -1 treated fruits was near the yellow colour.The highest b* values (33.71) were observed in control fruits in the second year, and effect of AVG concentrations was determined statistically significant (P<0.001).Previous studies showed that the effects of AVG treatment on fruit colour varied.Singh et al (2003) found that AVG treatments had no significant effects on the fruit colour of 'O'Henry' and 'Summerset' peach types, but that the red colour on the yellow surface increased on 'Zee Lady' peach type, implying that the effect of AVG treatments on colour development changes according to the type.
SSC and TA: Effects of the AVG applications on soluble solid contents (SSC) and titratable acidity (TA) changes are shown in Table 4. times on SSC and TA were not statistically significant.A study was carried out with 'O'Henry', 'Summerset', 'Zee Lady' and 'Elegant Lady' peach types.In this study, it was found that AVG spraying 15, 10 and 5 days before the harvest increased the SSC and TA amounts only of 'O'Henry' and 'Summerset' types (Singh et al 2003).

Ethylene production and respiration rates
AVG applications significantly reduced the ethylene rate of the fruits (Table 5).In the first year, the effects of AVG concentrations on ethylene production rate of fruits were found statistically significant (P<0.001).The ethylene production of control group fruits showed the highest value (0.76 µl kg -1 h -1 ) while 21 DBH-100 mg l -1 AVG fruits had the lowest value (0.18 µl kg -1 h -1 ).The interaction between concentrations and application times on the fruit ethylene production rate were found statistically significant (P<0.05) in the second year.The highest ethylene production was found in 30 DBH-control fruits (1.09 µl kg -1 h -1 ) and 30 DBH-200 mg l -1 AVG fruits showed the lowest value (0.10 µl kg -1 h -1 ).In the first year, the interaction between concentrations and times on the fruit respiration a-e : Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05) 185 rates were found statistically significant (P<0.05)(Table 5).In the second year, the effects of AVG concentrations on respiration rates of fruits were found statistically significant (P<0.001).The 30 DBH-100 mg l -1 AVG fruits showed the lowest value in the first year (4.71 ml CO 2 kg -1 h -1 ) and 7 DBH-100 mg l -1 AVG fruits showed the lowest value (5.53 ml CO 2 kg -1 h -1 ) in the second year.Similar to our Kim et al (2004a) found that AVG application decreased the ethylene production and respiration rate in the 'Mibaekdo' peach type, and Bregoli et al (2002) found the similar findings for the 'RedHaven' peach type.Moreover, they found no significant effects between application concentrations.3.4.Total sugar, reducing sugar and sucrose Total sugar, reducing sugar and sucrose values were given in Table 6.Statistically significant the interaction effects between concentrations and application times on the fruit total sugar (P<0.01 in first year, P<0.001 in second year), reduction sugar (P<0.001 in both years) and sucrose contents (P<0.01 in first year, P<0.001 in second year) were found.In the first year, the highest total sugar content was found in 7 DBH-control fruits.

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In second year, the total sugar content of fruits treated with 30 DBH-100 mg l -1 (11.50%) was higher than with the other treatments in the second year.30 DBH-200 mg l -1 (5.06%) treated fruits (in the first year) and 21 DBH-control (5.21%) fruits (in the second year) had the lowest total sugar content.In the first year, in general, the reduction in the sugar content of AVG-treated fruits and of control fruits were similar.The highest reduction in sugar content (2.57%) was in 30 DBH-control fruits.In the second year, 30 DBH-100 mg l -1 AVG fruits had the highest sugar content reduction.The sucrose contents of fruits were decreased by AVG treatments in the first year.The lowest sucrose content had 30 DBH-150 mg l -1 (in the first year) and the sucrose content of fruits which were treated with 30 DBH-100 mg l -1 treatments were lower than the other treatments (in the second year).Colarıč et al (2004) reported that total sugar and sucrose content varied from 6.15 to 9.37% and from 4.61 to 7.01% in peach and nectarine cultivars, respectively.In the current study, the total sugar content was between 5.06-11.50%, the reduction in sugar content was between 2.52-9.50% and the sucrose content was between 1.94-5.00%.Chapman & Horvat (1990) reported that the sucrose content of the 'Monroe' peach was around 7-8% at harvest.In the current study, the effect of AVG on sugar content showed no clear trend for application times and concentrations.

Leaf Area Index (LAI) and total chlorophyll, chlorophyll a, chlorophyll b in leaf
Mean values of leaf Area Index (LAI) in Table 7 and total chlorophyll, chlorophyll a, chlorophyll b in leaf in Table 8 were given.Leaf area was significantly affected by AVG treatments in both years.In first and second year, the interaction between concentrations and times on the fruit total sugar, reduction sugar and sucrose contents were found statistically significant (P<0.001).The highest LAI was found at 21 DBH-100 mg l -1 fruits (in the first year), and leaves treated with 30 DBH-200 mg l -1 were larger than the other groups (in the second year) (Table 7).In the first year, the total chlorophyll was increased by AVG treatments, but in the second year it was decreased.A similar trend was observed for chlorophyll a and chlorophyll b (Table 8).Only in second year, effect of AVG concentrations (P<0.001) and times (P<0.05) on total chlorophyll, chlorophyll a, chlorophyll b of leaves were found statistically significant.In this study, the total chlorophyll content of peach leaves was 0.80-2.24mg g -1 , the chlorophyll a content was 0.79-1.48mg g -1 and the chlorophyll b content was 0.28-0.77mg g -1 .These findings were found similar to the chlorophyll contents reported by Mordoğan & Gönülsüz (2000).

Conclusion
Obtained results are very important to reduce harvesting expenses and to improve uniformity of fruit maturity in a shorter time.These findings could bring great benefits for the marketing of peaches.As a result, regarding effects on weight, firmness and ethylene production as the time of application in terms 30 days before commercial harvest and 100 or 200 mg l -1 AVG concentration for 'Monroe' peach varieties can be recommended.

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Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05) Aminoethoxyvinylglycine' nin 'Monroe' Şeftali Çeşidinde Hasat Zamanı ve Meyve Kalitesi Üzerine Etkileri, Çetinbaş & Koyuncu T a r ı m Bi lim ler i D e r g i si -J o u r n a l o f A gr i cu l tu r a l S ci e n ce s 17 (2011) 177-189

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Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05) Effects of Aminoethoxyvinylglycine on Harvest Time and Fruit Quality of 'Monroe' Peaches, Çetinbaş & Koyuncu T a r ı m Bi lim ler i D e r g i si -J o u r n a l o f A gr i cu l tu r a l S ci e n ce s 17 (2011) 177-189

Table 2 -Fruit weight and firmness in 'Monroe' peaches at harvest as affected by treatment date and AVG concentration
Çizelge 2-AVG dozu ve uygulama zamanın ve 'Monroe' şeftalisinde meyve ağırlığı ve sertliğine etkisi Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05).

Table 7 -LAI in leaf of 'Monroe' peaches at harvest as affected by treatment date and AVG concentration
Çizelge 7-AVG dozu ve uygulama zamanın ve 'Monroe' şeftalisinin yaprak alan indeksine etkisi Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05)

Table 8 -Total chlorophyll, Chlorophyll a and Chlorophyll b in leaf of 'Monroe' peaches at harvest as affected by treatment date and AVG concentration
Values in a same column for each effect followed by different letters are significantly different (Duncan, P ≤ 0.05)