Impaginato 11 1. Introduction The polyamines as natural compounds are pre- sent ubiquitously in almost all living organisms. The m a i n p o l y a m i n e s i n s i g n i f i c a n t a m o u n t s a r e putrescine, spermidine, and spermine which are cru- cial for the growth and development of plant and fruit as well as stress responses (Valero and Serrano, 2010). They are known as anti-senescent agents that decrease the rate of fruit softening and senescence by suppression of ethylene production (Kramer et al., 1991). Reduced values of polyamines have been attributed with enhanced ethylene production and vice versa (Walden et al., 1997). This mechanism is correlated to a competition between polyamine and ethylene for the common precursor S-adenosyl methionine (SAM) (Pandey et al., 2000). The use of polyamines has been claimed to decrease ethylene synthesis in a wide range of plants by decreasing ACC synthase (ACS) and ACC oxidase (ACO) enzymes activ- ities (Ke and Romani, 1988; Kakkar and Rai, 1993; Lee et al., 1997; Martinez-Romero et al., 2001; Bregoli et al., 2002; Perez-Vicente et al., 2002; Serrano et al., 2003; Petkou et al., 2004; Malik and Singh, 2005; De Dios et al., 2006; Khan et al., 2007). In several investigations putrescine applied exoge- nously have been reported to increase storage life and quality attributes of mango (Razzaq et al., 2014), pear (Franco-Mora et al., 2005), apricot (Martinez- R o m e r o e t a l . , 2 0 0 2 ) , s t r a w b e r r y ( Z o k a e e Khosroshahi et al., 2007), plum (Abu-Kpawoh et al., 2002; Pérez-Vicente et al., 2002), grapes (Harindra Champa et al., 2015; Mirdehghan and Rahimi, 2016), pomegranate (Mirdehghan et al., 2007; Barman et al., 2011) and litchi (Jiang and Chen, 1995). Therefore, the aim of this study was to investigate the role of preharvest putrescine treatment on main- taining postharvest quality of pear fruit cv. Spadona. 2. Materials and Methods The experiments were conducted on pear trees (P. communis cv. Spadona) in the center of horticul- tural research of the University of Tehran, Karaj, Iran. Eighteen 16-year-old trees (250 cm height) were selected in terms of uniformity in size and fruit load then sprayed with putrescine at 0.5, 1 and 2 mM (3.5 Adv. Hort. Sci., 2017 31(1): 11-17 DOI: 10.13128/ahs-20720 Effect of pre-harvest putrescine treatment on quality and postharvest life of pear cv. Spadona M.S. Hosseini (*), Z. Fakhar, M. Babalar, M.A. Askari Department of Horticulture Science, College of Agriculture and Natural Resources, University of Tehran, 31587 Karaj, Iran. Key words: cold storage, color, fruits, quality assessment. Abstract: The study was conducted to determine the effect of pre-harvest foliar spraying with putrescine (at 0.5, 1 and 2 mM) on quality and postharvest life of Pyrus communis cv. Spadona during cold storage. Fruit quality assessment such as weight loss, firmness, total soluble solids (TSS), titratable acidity (TA), flavor index, skin color (L*, hue angle), vitamin C total phenol (TP), and total antioxidant activity (TAA) were made at harvest and after 3, 6, 9, 12, 15, 18 and 21 weeks of storage at 0±1°C, 80-85% relative humidity. Weight loss, fruit softening, TSS and pH increased during storage but the rate of changes was significantly lower in fruit treated with putrescine at 1 and 2 mM. Putrescine application maintained higher levels of TA, vitamin C, TP, TAA, L*, hue angle and reduced decay incidence compared to control. Furthermore, higher doses of putrescine were effective in terms of prolonging the storage and marketability of fruits more than 127- 142 days. In conclusion, pre-harvest application of putrescine could be an effective means for extending the postharvest life of pear cv. Spadona. (*) Corresponding author: m.hosseini79@yahoo.com Received for publication 28 August 2016 Accepted for publication 12 December 2016 Copyright: © 2017 Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2017 31(1): 11-17 12 L per tree) at different stages of fruit development in May, June, and July. Six trees sprayed with water (3.5 L per tree) were used as control. Fruits were harvest- ed manually and transported to the postharvest labo- ratory, and selected for absence of visual symptoms of disease or blemishes, then stored (5 fruits per bas- ket) at 0±1°C, 80-85% RH for 21 weeks. Quality attrib- utes were measured in five fruits of each replicate at harvest and after 3, 6, 9, 12, 15, 18 and 21 weeks of cold storage. Fruit quality assessments Fruit color changes were calculated at two oppo- site sides of fruit with a Minolta Chroma Meter CR- 400 (Osaka, Japan). The values of L*(0 - black; 100 - white), a* (green to red), b* (blue to yellow) and hue angle (h°=180 + tan-1 b*/a*, if a* < 0) were recorded (Fernando et al., 2007; Pek et al., 2010). The percentage of weight loss was recorded by using following equation: % weight loss = (A-B)/B × 100 in which A was the initial fruit weight and B was the final fruit weight. Fruit firmness was determined using a penetrometer FT327 (GFFECI, Italy) fitted with an 8 mm tip on the equatorial position of fruit. The results were expressed in newton (N). Total soluble solids (TSS) in the extracted juice of each treatment were measured by a refractometer (Atago N1, Japan) at 20°C and the result was record- ed as percentage. Five ml of diluted juice titrated a g a i n s t 0 . 1 N N a O H t o p H 8 . 2 t o a s s e s s T A . Phenolphthalein was used as an indicator. The TA was expressed as malic acid percentage (Saini et al., 2001). The pH of fruit juice was calculated using a MTT65 (Japan) pH meter calibrated by pH 4 and 7 buffer solutions. Flavor index was estimated by divid- ing TSS with the corresponding TA value. Vitamin C was measured using the procedures of Tian et al. (2002). Total phenol (TP) content and total antioxidant activity (TAA) TP and TAA were assessed according to Koushesh Saba et al. (2012). Decay incidence determination Fruit decay was determined based on the proce- dure of Khademi and Ershadi (2013). Scales from 1 to 5 were given to individual treatment group whereas: 1= normal (without decay), 2= (up to 5 % decay), 3= (5-20 % decay), 4= (20-50% decay) and 5= (more than 50% of fruits skin was decayed). Statistical analysis This experiment was conducted in a randomized experimental design with three levels of putrescine (0.5, 1 and 2 mM), using plants sprayed with water as control in three replications and two trees in each experimental unit. To estimate storability of pear fruit cv. Spadona, a factorial design in completely randomized were carried out and the experimental data analyzed using SAS statistical software package 9.4 for windows and mean comparisons were con- ducted using Duncan’s multiple range tests. 3. Results and Discussion Color A high rate of color changes was observed in con- trol fruits and 0.5 mM putrescine treated fruits, whereas, they exhibited lower L* and hue angel than others during storage (Fig. 1 A and B). Therefore, the conversion rate of green to yellow and degradation Fig. 1 - The effect of putrescine at different concentrations on L* (a) and hue angle (b) of pear cv. Spadona along the storage. Values are the mean ± SE. Hosseini et al. - Putrescine application for improving storage life of pear 13 of chlorophyll were shown slower in putrescine treat- ed fruits by 1 and 2 mM. The effect of putrescine in retarding skin color changes throughout the storage by decreasing senescence rate has also been report- ed in table grape (Harindra Champa et al., 2015), and pomegranate (Barman et al., 2011). Weight loss and firmness The weight loss increased in all fruit samples dur- ing the 21 weeks cold storage. As shown in figure 2 A, putrescine at 1 and 2 mM reduced the weight loss value than control at the end of storage. However, fruit treated with 2 mM putrescine showed inferior weight loss which started at the third sampling date (6th week), while it was not seen in those treated with 1 mM before the fifth sampling date (12th week). Reduction of weight loss in putrescine treated fruits can be ascribed to conjugation of polyamines to the cell membrane phospholipids and consequent- ly stabilization as well as consolidation of both cell integrity and permeability (Barman et al., 2011; Mirdehghan and Rahimi, 2016). Irrespective of treat- ments, fruit firmness decreased with the advance- ment of storage but putrescine treatment at 1 and 2 mM maintained highest fruit firmness compared to control (Fig. 2B). It is suggested that polyamines maintain fruit firmness by their cross-linkage to the pectin substances carboxyl groups in the cell wall and lead to strengthening of cell wall and consequently decreasing cell wall degrading enzymes activities of pectin methyl esterase (PME), pectin esterase (PE) and polygalactouronase (PG) (Valero et al., 2002). The role of putrescine in reducing weight loss and maintaining fruit firmness has been reported for peach (Zokaee Khosroshahi and Esna-Ashari, 2008) and pear (Franco-Mora et al., 2005). TSS, TA, pH and flavor index The contents of TSS (in the first 12 weeks of stor- age), pH and flavor index increased in all treated and untreated fruits while TA showed reverse trend along the storage. However, the lowest TSS, pH and flavor index were observed in treated fruits by 1 and 2 mM (Fig. 3 A, B, C and D). The role of putrescine on main- taining TSS, TA and pH in treated fruits would be attributed to the reduction of respiration rate (Valero et al., 2002), ethylene synthesis (Barman et al., 2011) and subsequently retarding the ripening process. Similar results have been reported in peach (Zokaee Khosroshahi and Esna-Ashari, 2008) and apricot (Enas et al., 2010). Vitamin C Vitamin C significantly declined as the storage advanced. However, this trend was slower in 1 and 2 putrescine treated fruits (Fig. 4). This effect can be associated with the property of putrescine on reduc- ing or delaying the activity of ascorbate oxidase and consequently maintaining vitamin C (ascorbic acid) content (Ishaq et al., 2009). Similar results have been reported in mango (Razzaq et al., 2014) and apricot (Davarynejad et al., 2013). Total phenol (TP) and total antioxidant activity (TAA) measurement Irrespective of treatments, total phenolic content and total antioxidant activity decreased at the end of storage; while these decreases were significantly higher at 1 and 2 mM putrescine treated fruits (Fig. 5 A and B). In spite of TAA, the TP changes were not constant during storage, it reached the highest value at the 9th week in fruits treated with 1 and 2 mM with the maximal values of 28 and 31 mg of GAE/100 g of FW at the 9th week respectively, then followed by reducing TP during the rest of storage period. Fig. 2 - The effect of putrescine at different concentrations on weight loss (a) and firmness (b) of pear cv. Spadona along the storage. Values are the mean ± SE. Adv. Hort. Sci., 2017 31(1): 11-17 14 Fig. 3 - The effect of putrescine at different concentrations on TSS (a), TA (b), pH (c) and flavor index (d) of pear cv. Spadona along the storage. Values are the mean ± SE. Fig. 4 - The effect of putrescine at different concentrations on vitamin C of pear cv. Spadona along the storage. Values are the mean ± SE. Fig. 5 - The effect of putrescine at different concentrations (0.5, 1 and 2 mM) on total phenol content (A) and total antioxidant activity (B) of pear cv. Spadona along the storage. Values are the mean ± SE. Hosseini et al. - Putrescine application for improving storage life of pear 15 The changes in the level of TP content may be associated to the breakdown of cell structure and subsequently senescence (Ghasemnezhad et al., 2010). The role of putrescine treatment to maintain TP could be ascribed to the delay of senescence process (Arora et al., 2002; Razzaq et al., 2014). As shown in figure 5, the value of TAA decreased along with a decrease of TP during storage. It may be ascribed to a direct correlation among TP content and TAA (Razzaq et al., 2014). However, putrescine treatment at 1 and 2 mM maintained TAA compared to control during storage. Similar results demonstrat- ed a positive correlation among TP and TAA in mango (Palafox-Carlos et al., 2012) and apricot (Ghasemnez- had et al., 2010). Decay incidence The lowest rate of fruit decay percentage was o b s e r v e d i n f r u i t s t r e a t e d w i t h 1 a n d 2 m M putrescine contrary to control at the end of storage (Fig. 6). It is suggested that polyamines have all requirements of an alternative approach for manage- ment of postharvest decay (Romanazzi et al., 2012). Storage life The application of putrescine at higher doses (1 and 2 Mm) extended storage life of pear fruits, and consequently they were suitable to be exposed in the market more than 127-142 days after the beginning of storage in comparison to control (109 days) (Fig. 7). 4. Conclusions T h e p r e - h a r v e s t a p p l i c a t i o n o f 1 a n d 2 m M putrescine treatment maintained the postharvest life of pear cv. 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