Timing of postharvest 1-methylcyclopropene treatment affects Bartlett pear quality after storage

Timing of postharvest 1-methylcyclopropene treatment affects Bartlett pear quality after storage Jennifer R. DeEll and Behrouz Ehsani-Moghaddam Ontario Ministry of Agriculture, Food and Rural Affairs, P.O. Box 587, Simcoe, Ontario, Canada N3Y 4N5 (e-mail: Jennifer.DeEll@ontario.ca). Received 31 March 2011, accepted 30 May 2011. DeEll, J. R. and Ehsani-Moghaddam, B. 2011. Timing of postharvest 1-methylcyclopropene treatment affects Bartlett pear quality after storage. Can. J. Plant Sci. 91: 853858. This study investigated the effects of postharvest 1-methylcyclopropene (1-MCP) treatment timing on the ripening and physiological disorders of Bartlett pears during cold storage and subsequent shelf-life. Pears were held for 1, 3 or 7 d at 38C after harvest and then treated with 0.3 mll 1 1-MCP for 24 h at 38C. Fruit quality attributes were evaluated after 4 mo of cold storage at 0.58C, plus 1 to 11 d at 228C. All 1-MCP treatments reduced ethylene production, as well as delayed fruit softening and yellow color development. However, the most substantial benefit of 1-MCP observed was the marked reduction in disorders, especially senescent scald and internal breakdown. The results suggest that 1-MCP treatment 3 d after harvest provided the best balance of reduced disorder development during storage and the ability of Bartlett pears to soften adequately thereafter. Fruit treated with 1-MCP at 1 d after harvest did not soften as much as those treated 3 or 7 d after harvest, while treatment after 7 d provided less control of disorders than treatment after 1 or 3 d. Key words: 1-MCP, ethylene, softening, disorders, shelf-life, Pyrus communis L. DeEll, J. R. et Ehsani-Moghaddam, B. 2011. Le moment du traitement post-re colte au 1-méthylcycloprope` ne affecte la qualite des poires Bartlett après l entreposage. Can. J. Plant Sci. 91: 853858. Cette e tude portait sur le moment du traitement post-récolte au 1-me thylcycloprope` ne (1-MCP) et son incidence sur le muˆrissement et les problèmes physiologiques des poires Bartlett durant la re frige ration ainsi que sur la durée de conservation subse quente. Les poires ont e te garde es 1, 3 ou 7 jours à une tempe rature de 38C apre` slarécolte, puis traite es avec 0,3 ml de 1-MCP par litre pendant 24 heures, à 38C. On a ensuite e value les parame` tres qualitatifs des fruits apre` s 4 mois d entreposage à 0,58C et1à 11 jours a` 228C. Tous les traitements au 1-MCP re duisent la production d e thylène et retardent l attendrissement du fruit et son jaunissement. Cependant, le principal avantage du 1-MCP consiste à réduire notablement les troubles physiologiques, notamment l e chaudure attribuable a` la sénescence et la de composition interne. Les résultats laissent croire que le traitement au 1-MCP trois jours apre` slare colte e quilibre le mieux un faible de veloppement des troubles physiologiques durant l entreposage à la capacite des poires Bartlett a` s attendrir correctement. Les fruits traite s avec du 1-MCP le jour suivant la cueillette ne s attendrissent pas autant que ceux traite s le3 e ou le 7 e jour, tandis que le traitement effectué apre` s sept jours ne controˆle pas aussi bien les troubles que ceux réalise s au bout de 1 ou 3 jours. Mots clés: 1-MCP, e thyle` ne, attendrissement, affections, durée de conservation, Pyrus communis L. 1-Methylcyclopropene (1-MCP) is a competitive inhibitor of ethylene action, as it binds irreversibly to ethylene receptors to regulate plant tissue responses to ethylene (Sisler and Serek 1997). Therefore, treatment with 1-MCP can delay fruit ripening and senescence, as well as associated processes such as respiration, ethylene production, color changes, softening, acidity loss, and volatile production (Watkins 2006). The efficacy of 1-MCP depends on several factors, such as concentration, duration, and temperature of exposure (Jiang et al. 1999; Mir et al. 2001; DeEll et al. 2002), fruit maturity at the time of treatment (Golding et al. 1998; Mir et al. 2001) and cultivar (Watkins et al. 2000). The inhibitory effects of 1-MCP on climacteric fruit ripening, such as apple (Watkins et al. 2000; DeEll et al. 2002, 2008a), banana (Harris et al. 2000), nectarine (Lurie and Weksler 2005; DeEll et al. 2008b), and plum (Dong et al. 2002; DeEll et al. 2008c), have been well documented. 1-MCP has been shown to inhibit ethylene production, retard respiration rate and delay or prevent softening in various pear cultivars (Kubo et al. 2003; Ekman et al. 2004; Trinchero et al. 2004; Mwaniki et al. 2005). Conclusions from a review on the ripening of European pears indicate that there is no clear understanding of the best combination of harvest maturity, 1-MCP concentration, application conditions (temperature and time), and storage time after 1-MCP treatment to adequately control fruit softening and the development of physiological disorders, while simultaneously allowing the fruit to ripen to good quality for marketing (Villalobos- Acun a and Mitcham 2008). There continues to be a risk of excessive inhibition of fruit ripening when using 1-MCP on European pears. Abbreviations: 1-MCP, 1-methylcyclopropene; SSC, soluble solids concentration Can. J. Plant Sci. (2011) 91: 853858 doi:10.4141/cjps2011-060 853

854 CANADIAN JOURNAL OF PLANT SCIENCE The degree of pear response to 1-MCP depends in part on the concentration of 1-MCP and the ripening ability of the cultivar. 1-MCP concentrations within 0.1 to 0.5 ml L 1 have shown the most potential for postharvest treatment to Bartlett pears (Ekman et al. 2004). Bartlett pears treated with 0.3 ml L 1 1-MCP on the day of harvest for 24 h at 208C recovered the ability to ripen only when fruit were subsequently stored in cold storage for more than 2 mo and then held at 10 to 208C for 10 or 20 d (Bai et al. 2006). Fruit temperature and 1-MCP treatment duration have also been shown to influence the response of Bartlett pears to 1-MCP, with treatment at 208C for 24 h being the most effective at inhibiting ripening (Villalobos-Acun a et al. 2011b). In this same study, there was little effect of temperature conditioning prior to 1-MCP treatment on fruit ripening after cold storage. The overall objective of this study was to evaluate the effects of postharvest 1-MCP treatment timing on fruit ripening after storage and the development of physiological disorders in Bartlett pears. More specifically, pears were held for 1, 3 or 7 d at 38C after harvest and then treated with 0.3 ml L 1 1-MCP for 24 h at 38C. It was thought that some time between harvest and 1-MCP treatment might alleviate the risk of non-ripening issues, while the treatment time and temperature represented the most practical scenario for commercial practice. MATERIALS AND METHODS Fruit Material and Treatments For two subsequent years, Bartlett pears (Pyrus communis L.) were harvested from a commercial orchard near Simcoe, Ontario, Canada. Harvests occurred within the middle of the commercial harvest period, which normally commences when fruit firmness is around 86 N (Slingerland et al. 2002). Three boxes from each of three trees (nine boxes total, 100 fruit each) of Bartlett pears were harvested in 2008, while four boxes from each of three trees (12 boxes total) were harvested in 2009. Five fruit per tree were used for maturity evaluations at harvest. Pears were transported within 30 min to the nearby storage research facility and held at 38C for 1 or 7 d in 2008, and 1, 3, or 7 d in 2009. Half of the boxes from each time period were then placed in a sealed air-tight treatment tent (Storage Control Systems Inc., Sparta, MI) and exposed to 0.3 ml L 1 1-MCP (SmartFresh SM, AgroFresh Inc., Spring House, PA) for 24 h at 38C. The 1-MCP concentration was calculated according to the percent active ingredient and release from SmartFresh powder (in 2008) or tablets (in 2009) into the volume of the tent. The concentration of 0.3 ml L 1 1-MCP is equivalent to the label rate of SmartFresh for pears in Canada. Following 1-MCP treatment, all pears were held at 0.58C for 4 mo. A total of 10 fruit from each tree and treatment combination (box, replicate) were evaluated for quality at each time point during subsequent holding at 228C. Fruit evaluations were made after 1, 4, 7, and 10 d at 228C in the first year, and after 1, 7, and 11 d in the second year. Fifty additional fruit from each replicate of each treatment were also evaluated for disorders on the last day of holding at 228C in both years. Fruit Quality Measurements Fruit firmness was determined on opposite sides of each pear after peel removal, using an electronic texture analyzer fitted with a 7-mm tip (GU SS, South Africa). Soluble solids concentration (SSC) was determined on a juice sample using a digital refractometer (PR-32, Atago Co., Ltd., Japan). Skin color was evaluated using a 1 to 4 scale, where 1green, 2 more green than yellow, 3 more yellow than green, and 4 yellow. Fruit diameter and length were also measured at harvest, as well as starch content, by using the generic starch-iodine test (Blanpied and Silsby 1992) and determining the percentage of starch staining. After storage, the incidence of senescent scald, internal breakdown, and friction marking was determined as a percentage of fruit with the disorder, regardless of severity. Ethylene Production Three pears from each replicate and treatment combination were placed into 9-L plastic containers and sealed air-tight for 30 min. A 3-mL gas sample was then withdrawn from the headspace of the container using a syringe inserted through a rubber septum. The gas sample was analyzed for ethylene using a Varian CP- 3380 gas chromatograph (Varian Inc., Mississauga, ON) equipped with a 0.5-mL sample loop, flame ionization detector (FID), and 15 m0.32 mm Restek Rt- SPLOT TM capillary column (Chromatographic Specialties Inc., Brockville, ON). The injector, column, and detector temperatures were 120, 35, and 2258C, respectively. High-grade helium was used as the carrier gas at a flow rate of 0.37 ml s 1 with a typical run time of 2 min. Statistical Analyses Data were analyzed by generalized linear models procedures using the SAS program (version 9.1.3, SAS Institute, Inc., Cary, NC). Mean separations were examined using Duncan s separation test and only differences significant at P B0.05 are discussed. RESULTS Bartlett fruit maturity at harvest is presented in Table 1. There was no measurable ethylene production at the time of harvest in both years. In general, 1-MCP-treated Bartlett pears produced less ethylene than untreated fruit during holding at 228C, after 4 mo of cold storage (Tables 2 and 3). There was no significant difference in ethylene production in pears treated with 1-MCP after 1 or 7 d from harvest in

DEELL AND EHSANI-MOGHADDAM * BARTLETT PEAR QUALITY AFTER STORAGE 855 Table 1. Maturity of Bartlett pears at harvest in 2008 and 2009 Year Ethylene production (ml kg 1 h 1 ) Firmness (N) Soluble solids Skin color z (14) Length (cm) Diameter (cm) Starch y 2008 0 75.6 10.8 1.1 8.5 6.0 63 2009 0 81.6 10.4 1.0 10.2 7.1 51 z Color scale: 1green, 2more green than yellow, 3more yellow than green, and 4yellow. y Starch : flesh stained with iodine. the first year (Table 2). Pears treated with 1-MCP at 1 or 3 d after harvest in the second year produced less ethylene following 1 and 7 d at 228C, compared with fruit treated 7 d after harvest (Table 3). After 11 d at 228C, there was no longer a significant difference in ethylene production among treated pears, regardless of treatment timing. 1-MCP-treated pears were firmer than untreated fruit after 4 mo of cold storage, but this effect was influenced by the timing of 1-MCP application and the duration of holding at 228C following cold storage. In the first year of study, pears treated with 1-MCP at 1 or 7 d after harvest had similar firmness after 1 and 4 d at 228C following removal from cold storage, while those not Table 2. Ethylene production, firmness, skin color, and soluble solids concentration of Bartlett pears treated without or with 1-MCP after 1 or 7 d following harvest, and held for 4 mo at 0.58C, followed by 1, 4, 7, or 10 d at 228C in 2008 Ethylene production (ml kg 1 h 1 ) Firmness (N) Skin color z (14) Soluble solids 1 day at 228C Control 24B 58D 3.1B 11.2G 1-MCP/1 d 14B 67AB 2.3D 11.2G 1-MCP/7 d 3B 70A 2.5D 11.7DE 4 days at 228C Control 62A 27G 3.7A 11.9C 1-MCP/1 d 2B 64BC 2.8C 12.4B 1-MCP/7 d 6B 63C 3.0BC 12.0C 7 days at 228C Control 71A 17H 3.8A 11.5F 1-MCP/1 d 24B 57D 3.1BC 11.6EF 1-MCP/7 d 12B 50E 3.6A 12.7A 10 days at 228C Control y 1-MCP/1 d 12B 51E 3.6A 11.8CD 1-MCP/7 d 11B 42F 3.8A 12.7A Significance Treatment (T) **** **** **** ** TDay *** **** **** **** z Color scale: 1green, 2more green than yellow, 3more yellow than green, and 4yellow. y Control fruit after 10 d at 228C had deteriorated with severe senescent scald and internal breakdown; therefore, no further quality measurements could be taken. **, ***, **** Significant at PB0.01, PB0.001, and PB0.0001, respectively. AG Means with the same letter within each column are not significantly different at PB0.05. treated softened substantially during this time (Table 2). After 7 or 10 d at 228C, pears treated with 1-MCP at 1 d after harvest remained firmer than those treated 7 d after harvest, while fruit from both treatments softened to the level that control fruit exhibited after 1 d at 228C. In the second year, all 1-MCP-treated pears were firmer than untreated fruit after 4 mo of cold storage, plus 1 or 7 d at 228C (Table 3). After 11 d at 228C, only pears treated with 1-MCP at 1 d after harvest remained firmer than untreated fruit. Skin color was greener in 1-MCP-treated pears after 4 mo of cold storage plus 1 or 4 d at 228C in the first year, compared with fruit not treated with 1-MCP (Table 2). However, after 7 d at 228C, pears treated with 1-MCP at 7 d after harvest exhibited similar color as those not treated, while fruit treated 1 d after harvest continued to be less yellow. Skin color was also greener in 1-MCP-treated pears than untreated fruit after storage in the second year of study (Table 3). However, differences among 1-MCP treatments and holding times were not consistent throughout 11 d at 228C. There was no consistent effect of 1-MCP on SSC in the first year of study, although some significant differences were found among the various treatments and times (Table 2). In the second year, all 1-MCPtreated pears had higher SSC than untreated fruit (Table 3). However, there was no consistent effect of the timing of 1-MCP application on SSC (Table 3). 1-MCP substantially reduced the amount of senescent scald and internal breakdown in Bartlett pears in both years of study (Table 4). 1-MCP also reduced the incidence of friction marking in the second year of study. Fruit treated with 1-MCP at 1 or 3 d after harvest had less incidence of internal breakdown and friction marking than those treated 7 d after harvest. DISCUSSION Delaying pear ripening and senescence to extend fruit storage and marketing periods without the appearance of physiological disorders is the most important potential benefit of 1-MCP application to pears after harvest (Villalobos-Acun a and Mitcham 2008). However, 1-MCP must be applied in such a way that pears ripen normally after a period of cold storage. It is important to note that the acceptable level of firmness for Bartlett pears can vary from 18 N as a ripeness threshold for fresh market (Ekman et al. 2004) to around 36 N for use in processing (Slingerland, personal communication).

856 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Ethylene production, firmness, skin color, and soluble solids oncentration of Bartlett pears treated without or with 1-MCP after 1, 3, or 7 d following harvest, and held for 4 mo at 0.58C, followed by 1, 7, or 11 d at 228C in 2009 Ethylene production (ml kg 1 h 1 ) Firmness (N) Skin color z (14) Soluble solids 1 day at 228C Control 113A 65B 3.0CD 11.6E 1-MCP/1 d 10F 73A 2.6EF 11.9CD 1-MCP/3 d 12F 71A 2.3F 11.8D 1-MCP/7 d 22E 73A 2.8DE 12.0C 7 days at 228C Control 38CD 32F 4.0A 10.6H 1-MCP/1 d 30D 65B 3.2BC 12.2B 1-MCP/3 d 22E 57C 3.1BC 11.7DE 1-MCP/7 d 51B 51D 3.2BC 12.2B 11 days at 228C Control 13F 30F 4.0A 10.9G 1-MCP/1 d 33CD 44E 3.3B 12.5A 1-MCP/3 d 36CD 28F 3.9A 12.4A 1-MCP/7 d 39C 29F 3.4B 11.3F Significance Treatment (T) * **** **** **** TDay **** **** **** **** z Color scale: 1green, 2more green than yellow, 3more yellow than green, and 4yellow. *, **** Significant at PB0.05 and PB0.0001, respectively. AH Means with the same letter within each column are not significantly different at PB0.05. Therefore, the required softening of Bartlett pears treated with 1-MCP can vary with product use. The rate at which fruit regains ethylene sensitivity is primarily dependent on 1-MCP concentration and storage duration (Watkins et al. 2000). Bartlett pears treated with 1 ml L 1 1-MCP the day after harvest and stored for 18 wk at 18C turned yellow but remained hard and inedible (Ekman et al. 2004). In this study, Bartlett pears treated with 0.3 ml L 1 1-MCP the day after harvest remained firmer than those treated 3 or 7 d after harvest, following 4 mo of storage at 0.58C plus 7 d at 228C (Tables 2 and 3). Furthermore, pears treated 3 or 7 d after harvest softened to the level of control fruit after 11 d at 228C in the second year of study (Table 3). The amount of time for 1-MCP-treated Bartlett to soften to acceptable levels tends to vary with the growing season, as suggested by the different softening rates during the 2 yr of this study. Fruit maturity at the time of harvest and the abundance of ethylene receptors in Bartlett at the time of 1-MCP treatment are key factors in the strength of the response to 1-MCP (Villalobos-Acun a et al. 2011a). Storage duration also affects the time for 1-MCP-treated Bartlett to soften to acceptable levels (Ekman et al. 2004; Bai et al. 2006). In the first year of this study, untreated pears required 7 d at 228C after 4 mo of storage at 0.58C to soften below the 18 N fresh market ripeness threshold (Table 2). Pears treated with 1-MCP did not reach this level of firmness after 10 d at 228C, but softening may have continued with more time. During the second year, untreated pears and those treated 3 or 7 d after harvest had softened to a similar and acceptable level for processing (B36 N) after 11 d at 228C (Table 3). However, none of the pears reached the 18 N fresh market threshold within the timeframe of the experiment. This suggests that fruit maturity at harvest may not have been adequate for proper ripening, even without 1-MCP. Treatment with 1-MCP on Bartlett pears of varying firmness (69 to 91 N) for 12 h at 208C immediately after harvest has been shown to reduce rates of fruit softening, yellow color development, ethylene production, and respiration (Villalobos-Acun a et al. 2011a). Subsequent ripening recovery was dependent on fruit maturity and growing season, and was associated with stimulated ethylene production and associated enzymes. Treatment with 0.3 ml L 1 1-MCP at 08C for 24 h was found to be more effective at inhibiting Bartlett ripening than that for 12 h, while 1-MCP treatment at 08C for 24 h was less effective than that at 208C (Villalobos- Acun a et al. 2011b). In the present study, 0.3 ml L 1 1-MCP for 24 h at 38C also effectively delayed yellow color development and reduced ethylene production (Tables 2 and 3). The timing of 1-MCP application had little influence on these effects and all treated pears had increased yellow color within 4 d at 228C following removal from cold storage. 1-MCP tends to have little effect on SSC (DeEll et al. 2002; Calvo and Sozzi 2004; Watkins and Nock 2005; Calvo and Sozzi 2009) and thus SSC response is usually given little consideration when evaluating 1-MCP efficacy. In the present study, SSC was often higher in 1-MCP-treated Bartlett pears than those not treated, and this effect was more consistent in the second year Table 4. Senescent scald, internal breakdown, and friction marking of Bartlett pears treated without or with 1-MCP after 1, 3, or 7 d following harvest, and held for 4 mo at 0.58C, followed by 7 or 11 d at 228C in 2008 or 2009, respectively Senescent scald Internal breakdown Friction marking 2008 Control 43A 13A 3 1-MCP/1 d 7B 0B 23 1-MCP/7 d 0B 0B 10 Significance **** **** NS 2009 Control 47A 100A 93A 1-MCP/1 d 4B 3C 14C 1-MCP/3 d 1B 5C 20C 1-MCP/7 d 11B 34B 42B Significance **** **** **** **** Significant at PB0.0001; NS, not significant. AC Means with the same letter within each column are not significantly different at PB0.05.

DEELL AND EHSANI-MOGHADDAM * BARTLETT PEAR QUALITY AFTER STORAGE 857 (Tables 2 and 3). Chen and Spotts (2005) also found that SSC in 1-MCP-treated d Anjou pears was slightly higher than in untreated fruit. The most substantial benefit of 1-MCP observed in this study was the marked reduction in disorders, especially senescent scald and internal breakdown. These results are in agreement with previous studies, in which 1-MCP reduced superficial scald and internal breakdown in Bartlett pears (Ekman et al. 2004; Villalobos-Acun a et al. 2011a), as well as senescent and core breakdown in other cultivars (Kubo et al. 2003; Calvo and Sozzi 2004). The storage life of Bartlett pears is usually limited due to the development of physiological disorders, and late harvested pears are especially susceptible (Ju et al. 2001). This makes 1-MCP a useful tool for extending storage life. The results of this study show that 1-MCP treatment 3 d after harvest provided the best balance of reduced disorder development during storage and the ability of Bartlett pears to soften adequately, at least for processing. Fruit treated with 1-MCP at 1 d after harvest did not soften as much as those treated 3 or 7 d after harvest, while treatment after 7 d provided less control of disorders than treatment after 1 or 3 d. Holding periods prior to 1-MCP treatment in order to optimize the effects on ripening and control of disorders have been established for other pear cultivars. For example, holding at 18C for 1 wk and then 4 d at 208C prior to treatment with 10 ml L 1 1-MCP provided the best balance of delayed softening and reduced senescent breakdown in La France pears (Kubo et al. 2003). In contrast, Villalobos-Acun a et al. (2011b) found that holding Bartlett for 3, 5, or 7 d at 0, 5, 10, 15, or 208C prior to treatment with 0.3 ml L 1 1-MCP had minor to no effect on ripening relative to untreated control fruit. It appears that ripening behavior and responses to ripening inhibitors may be different in pears grown in different locations and environments. Bartlett pears from growing regions with cooler preharvest temperatures exhibit higher ethylene production rates during ripening, indicating differences in the ability to ripen (Agar et al. 1999). Therefore, similar pears from different growing areas may not always respond the same to 1-MCP treatment. For relatively cooler growing regions, such as the location of this study, postharvest treatment with 1-MCP 3 d after harvest provides a good balance of delayed ripening and reduced disorder development during storage, with the ability of Bartlett pears to soften thereafter. 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