GIBBERELLIC ACID (GA3) EFFECTS ON LATE SEASON GRAPEFRUIT PEEL OIL COMPOSITION

Transcription

1 51 GIBBERELLIC ACID (GA3) EFFECTS ON LATE SEASON GRAPEFRUIT PEEL OIL COMPOSITION Peter D. Petracek 1, Daqing Sun 2, Huating Dou 3, Ed Stover 4 1 Valent BioSciences Corporation, Libertyville, IL Valley Research, Inc., South Bend, IN OSI Group, Visalia CA USDA, Ft. Pierce, FL ABSTRACT Gibberellic acid (GA 3 ) is commonly applied to citrus fruit in the late summer/early autumn to delay peel maturation and extend late season quality. The effect of August/September GA 3 application on oil gland composition of "Marsh" white grapefruit harvested in March 18 and April 16 from three groves was examined by capillary GC/MS analysis of 25 constituents. In the March harvest, GA 3 significantly increased limonene and significantly decreased linalool and trans-caryophyllene. In the April harvest, GA 3 significantly increased phellandrene, limonene, trans-linalool oxide and significantly decreased sabinene, β-pinene, linalool, α-terpineol, trans-caryophyllene, and nootkatone. With respect to changes in percent composition, limonene increased and nootkatone decreased the most with GA 3. Harvest date had the greatest effect on limonene levels in which levels decreased for the later harvest date. GA 3 significantly reduced postharvest pitting incidence of the March 18 harvest, but not the April 16 harvest. Grove significantly affected both oil composition and postharvest pitting for both harvests. Sabinene and ocimene levels were relatively low in the grove with the lowest postharvest pitting incidence. Keywords: PGR, GA3, gibberellic acid, oil gland composition, citrus peel, storage quality, postharvest pitting. INTRODUCTION Citrus fruit senescence involves pigment changes and rind tissue softening (1) which significantly reduce value of late-season grapefruit (Citrus paradisi). The rind disorder known as postharvest pitting, characterized by clusters of collapsed oil glands that develop over the surface of the fruit (2), also tends to be greater as fruit approaches senescence. The synthesis of nootkatone, one of the gland oil sesquiterpenes, has been positively correlated with the maturation-senescence process in C. paradisi fruit (3). The growth regulator gibberellic acid (GA 3 ) is widely used on citrus in many parts of the world to retard peel senescence and reduce fruit drop (4). Foliar application of GA 3 during grapefruit color break (August/September) does not affect postharvest internal levels of O 2, CO 2, ethanol, or acetaldehyde or weight loss of fruit harvested in March and April (5). However, these early season foliar applications of GA 3 significantly delayed the loss in firmness and color change of grapefruit during storage (Dou, personal communication) as well as reduced or delayed postharvest pitting in Falglo tangerines and white grapefruit (5). This study was conducted to determine whether effects of GA 3 on peel characteristics may be mediated through changes in peel oil composition. EXPERIMENT Plant materials Trees used in this study were Marsh white grapefruit (Citrus paradisi Macf.) on citrumelo rootstocks (C. paradisi Macf. x Poncirus trifoliata L.), growing near Ft. Pierce in the Indian River Citrus Region of Florida (see Table 1 for details). Swingle rootstock was used in Groves 1 and 2 108

2 and F80-8 rootstock in Grove 3. Healthy representative trees were selected in each grove for use in the study. All groves were on double beds on sandy soils with sporadic hardpans typical of Indian River citrus production. (Grove 1 and 3 were on Pineda Sand and Grove 2 was on Riviera Sand depressional). Groves 1 and 3 were microsprinkler irrigated and received pesticide typical for fresh grapefruit production, while Grove 2 was flood irrigated and managed as a semi-abandoned grove with possible sale of fruit for processing and received only a summer oil spray during the study period. All groves received fertilization typical for fresh grapefruit production with kg ( lbs/a) of nitrogen per hectare per year. Plant growth regulator applications The effect of GA 3 application on peel pitting was studied in the growing seasons. The field experiments were established using randomized complete block design, with blocking occurring spatially in each grove and each treatment applied to 3 replications with 2-5 trees per experimental unit. All applications were made using air-blast sprayers. Groves 1 and 2 were sprayed using a three-point hitch, PTO-driven airblast sprayer (Rears Mini-Blast, Eugene, OR) with a single side volute to increase wind velocity. Grove 3 was sprayed with an engine-driven sprayer (Durand Wayland AF500CPS, Lagrange, Georgia). All groves received treatment prior to color-break with GA 3 at 49.4 g GA 3 /hectare (ProGibb, Valent BioSciences Corporation, Libertyville, Illinois), with 0.05% v/v surfactant (Silwet L-77, Loveland Industries, Greely, Colorado) or left non-sprayed. Postharvest handling On the day after harvest, fruit were washed on roller brushes with FMC Fruit Cleaner 395 (FMC Corporation, Lakeland, Florida), but were not exposed to ethylene for degreening or treated with fungicide. Fruit sampled for oil composition were taken from the packingline, packed in 20 x 40 x 60 cm cardboard boxes and stored at 21 C and 93% RH for oil analysis. Postharvest pitting Additional fruit were coated with commercially-available water-waxes with wax solid composition comprised primarily of shellac (FMC Corporation, Lakeland, Florida) on roller brushes. Fruit was packed in 20 x 40 x 60 cm cardboard boxes and stored at 21 C and 93% RH. Pitting incidence was defined as percent of fruit with at least 10 collapsed oil glands per fruit (n = 3 replicate boxes with 18 fruit per box). Fruit were evaluated 4 weeks after wax application. Extraction of peel oils Extraction and chromatography of oil samples was executed as soon as possible after harvest. Sampling was done on a per replication basis to reduce the effect of fruit storage time. Fluid from three to five intact oil glands was extracted from the middle of the stylar end and equator of the fruit with a syringe and dissolved in 0.1 ml of methylene chloride. Two microliters of the solution was injected immediately for GC analysis (6). Six fruit were sampled for each treatment. Chromatography Samples were analyzed on a Hewlett-Packard 5890 high resolution capillary gas chromatography with a 0.32 mm internal diameter x 30 m DB-5 column (Restek, Bellefonte, PA). The initial oven temperature was 32 C, held for 5 min, then ramped at 7 C min -1 until reaching 260 C and held there for 5 min. The injector temperature was 260 C, the detector 260 C and the hydrogen carrier gas flow was 50 cm/sec. Retention index values were established using standards. Peaks were identified by using retention indices and by mass spectral information obtained from standards and the literature (6). Statistical analysis Factorial analysis was performed using PlotIT (SPE, Haslett, MI). RESULTS AND DISCUSSION Levels of volatile components were characterized in white grapefruit peel oil for the March 18 (Table 2) and April 16 (Table 3) harvests at three groves in the Indian River area of Florida. In the March harvest, 109

3 GA 3 significantly increased limonene and significantly decreased linalool and trans-caryophyllene. Grove significantly affected sabinene, β-pinene, limonene, and δ-cadinene. In the April harvest, GA 3 significantly increased phellandrene, limonene, trans-linalool oxide and significantly decreased sabinene, β-pinene, linalool, α-terpineol, trans-caryophyllene, and nootkatone. Grove significantly affected α-pinene, sabinene, β-pinene, ethyl-hexanoate, α-phellandrene, 3-carene, limonene, nonanal, α-copaene, dodecanal, δ-cadinene, and nootkatone. With respect to changes in total percent composition, limonene and nootkatone changed the most with GA 3 application. Across grove and harvest dates, GA 3 application increased limonene levels 0.75% of the total analyzed oil composition (92.63% vs % for UTC and GA 3 treatments, respectively) and decreased nootkatone levels 0.33% of the total analyzed oil composition (0.90% vs. 0.57% for UTC and GA 3 treatments, respectively). Limonene levels changed the most among the peel oils assessed. Between the two harvest dates, limonene levels decreased 1.2% of the total analyzed oil composition across GA 3 treatment and grove (93.6% vs. 92.4% for March 18 and April 16 harvests, respectively). For both harvests, linalool levels were decreased by GA 3 application by 48% across groves and harvest date. Linalool is one of the most phytotoxic gland oil (7). A therefore reduction of linalool following GA 3 application may play a role in GA-mediated reduction in postharvest pitting. GA 3 decreased nootkatone levels (Table 2) by 49%, 25%, and 63% in groves 1, 2, and 3, respectively. Since GA 3 decreases senescence a previous study demonstrated that other processes which delay maturation-senescence such as cold storage and wax application also decrease nootkatone levels (8). While Thomas et al (1993) showed that ethylene or ethylene-releasing agents, which are capable of increasing senescence in Citrus paradisi, increased nootkatone levels (9). All these reports are consistent with nootkatone serving as a reliable indicator and/or predictor of grapefruit senescence. The peel oil in grapefruit contributes to the characteristic flavor of grapefruit juice because some oil is introduced into the juice during extraction. Among compounds that show treatment effects (Table 1), α- terpineol contributes negatively to grapefruit flavor (9), and was reduced an average of 80% by GA 3 treatment. Grove significantly affected levels in 12 out of the 25 peel oil compounds in the April 16 harvest (Table 3). The interaction between grove and GA 3 treatment was significant for 6 peel oil compounds listed in Table 3. It should be noted that Grove 1 responded differently from Groves 2 and 3 in 4 of the 6 cases of significant interaction, and this grove was not managed for commercial fresh fruit production, receiving fewer sprays and poorer water management than the other two sites. GA 3 significantly reduced postharvest pitting incidence for the March 18 harvest (27.7% vs. 16.0% for the control and GA 3 treated respective), but GA 3 did not the April 16 harvest (32.0% vs. 29.7% for the control and GA 3 treated respective; Table 4). Overall postharvest pitting incidence was relatively high in these trials and the incidence increased with harvest date (22.7% vs. 31.0% for harvests of March 18 vs. April 16, respectively). This suggests that the effect of GA 3 on postharvest pitting may be time limited. Petracek and Davis (1996) found that Grove / location can significantly influence the incidence of postharvest pitting (10). Grove 1 had the lowest postharvest pitting of the three groves (Table 4). Among the peel oil compounds with more than 0.10% of the total composition, sabinene and ocimene levels were 110

4 the most different for Grove 1 vs. Groves 2 and 3 (Tables 2 and 3). While the differences are not consistent across GA 3 treatment and harvest date, particularly for ocimene, the lower levels of these two oils in Grove 1 may be an indicator of susceptibility. Postharvest pitting incidence greatly increases with wax application and high temperature storage (2). In previous research, we showed that wax application decreased nonanal and nootkatone levels and high temperature storage increased β-pinene, α-phellandrene, 3-carene, ocimene, octanol, trans-linalool oxide, and cis-p-mentha-2,8-dien-1-ol levels but decreased limonene (11). The association among decreased ocimene levels due to wax application (11) and Grove 1 lower ocimene levels (Tables 2 and 3) and reduced lower postharvest pitting susceptibility (Table 2) further suggests ocimene may be an indicator of susceptibility. An indicator or marker for postharvest pitting susceptibility could be useful in studying the disorder and determining ways to reduce postharvest losses (12). More work is required to determine the mechanism behind the grove effects on postharvest pitting and on peel oil composition. The fact that GA 3 treatments, grove conditions, wax application, storage time, and storage temperature all affect postharvest pitting, senescence and peel oil composition suggests that postharvest pitting, senescence and peel oil composition are related. A better understanding of this relationship may permit the use of peel oil composition as predictor of postharvest pitting and senescence, and may ultimately suggest grove management practices, including GA 3 application, to manipulate peel oil composition for reduced postharvest pitting and possibly other desirable traits. ACKNOWLEDGEMENTS We are thankful to Dr. Steven Nagy for his help and keen interest in the work. REFERENCES 1. C. W. Coggins Jr. and G. L. Henning, A comprehensive California field study of the influence of preharvest applications of gibberellic acid on the rind quality of Valencia oranges. Israel J. Bot., 37, (1988). 2. P. D, Petracek, W. F. Wardowski and G. E. Brown, Pitting of grapefruit that resembles chilling injury. HortScience 30: (1995). 3. J. A. Del Rio, A. Ortuno, D. Garcia Puig, L. Porras, A. Garcia-Lidon and F. Sabater, Variations of nootkatone and valencene levels during the development of grapefruit. J. Agric. Food Chem., 40, (1992). 4. R. E. McDonald, P. D. Greany, P. E. Shaw and T. G. McCollum, Preharvest applications of gibberellic acid delay senescence of Florida grapefruit. J. Hort. Sci., 72, (1997). 5. P. D. Petracek, H. Dou, and E. Stover, The influence of gibberellic acid (GA) on postharvest pitting of citrus. HortScience, 33, 519 (1998). 6. D. Sun and P. D. Petracek, Grapefruit gland oil composition is affected by wax application, storage temperature, and storage time. J. Agric. Food Chem. 47: (1999). 7. B. Wild, Oils Ain t Oils in Citrus Rinds. Australian Citrus News, 6, 9-11 (1992). 8. A. O. Tomas, D. Garcia-Puig, F. Sabater, I. Porras, A. Garcia-Lidon and J. A. Del Rio, Influence of Ethylene and Ethephon on the sesquiterpene nootkatone production in Citrus paradisi. J. Agric. Food Chem. 41, (1993). 9. J. Pino, R. Torricella, F. Orsi, Correlation between sensory and gas-chromatographic measurements on grapefruit juice volatiles. Nahrung, 30, (1986). 10. P. D. Petracek and C. Davis, Effects of selected preharvest factors on postharvest pitting of white grapefruit. Proc. Fla. State Hort. Soc. 10, (1996). 111

5 11. P. D. Petracek, D. F. Kelsey and W. Grierson, Physiological peel disorders. Fresh Citrus Fruits. W. F. Wardowski, W. M. Miller, D. J. Hall and W. Grierson. Longboat Key, Florida, Florida Science Source, Inc (2006). 112

6 Table 1. Details of field applications of GA 3 to Indian River grapefruit in Grove 1 Grove 2 Grove 3 Soil type Riviera Sand depressional Pineda Sand Pineda Sand Irrigation Flood Microsprinkler Microsprinkler Pest management Processing fruit (semiabandoned). Only one summer oil spray. Fresh fruit- 5 sprays per year for fungal pests and arthropod control as needed Fresh fruit- 5 sprays per year for fungal pests and arthropod control as needed Sprayer used Rears Miniblast Rears Miniblast Durand Wayland AF500CPS Spray volume 2300 L. ha -1 (250 GPA) 2300 L. ha -1 (250 GPA) 1400 L. ha -1 (150 GPA) GA 3 application 21.5 ppm applied twice 21.5 ppm 35.3 ppm Precolor break sprays Nontreated GA 3 +surfactant y Applied 9 and 19 Sep., 1997 z GA3 (ProGibb 4%): 9.4 g GA 3. ha -1 Nontreated GA 3 +surfactant Applied 20 Sep., 1997 Nontreated GA 3 +surfactant Applied 22 Aug., 1997 y Surfactant: Silwet L-77 at 0.05% (v/v) 113

7 Table 2. Percentage composition of grapefruit peel oil affected by GA 3, grove (GR), or the interaction (GA 3 x GR) March 18 harvest. Grove 1 Grove 2 Grove 3 Significance Compounds No GA 3 No GA 3 No GA 3 GA 3 GR GA 3 xgr α-pinene sabinene *** β-pinene *** myrcene ethyl-hexanoate * octanal α-phellandrene * 3-carene limonene * *** ocimene γ-terpinene cis-linalool oxide trans-linalool oxide linalool * nonanal citronellol α-terpineol decanal neral α-copaene dodecanal trans-caryophyllene * α-humumlene δ-cadinene * nootkatone Factors GA 3 and GR represent GA 3 application and grove effect, respectively. *, **, *** represent confidence level of 95%, 99%, 99.9%, respectively (n = six fruit sampled for each treatment). 114

8 Table 3. Percentage composition of grapefruit peel oil affected by GA 3, grove (GR), or the interaction (GA 3 x GR) April 16 harvest. Grove 1 Grove 2 Grove 3 Significance Compounds No GA 3 No GA 3 No GA 3 GA 3 GR GA 3 xgr α-pinene * sabinene *** *** ** β-pinene ** *** * myrcene ethyl-hexanoate *** ** octanal α-phellandrene * 3-carene ** ** *** limonene *** * ocimene * γ-terpinene cis-linalool oxide trans-linalool oxide * linalool ** nonanal * citronellol α-terpineol *** decanal neral α-copaene *** dodecanal * * trans-caryophyllene *** α-humumlene δ-cadinene *** nootkatone *** * Factors GA 3 and GR represent GA 3 application and grove effect, respectively. *, **, *** represent confidence level of 95%, 99%, 99.9%, respectively (n = six fruit sampled for each treatment). 115

9 Table 4. Percentage incidence of postharvest pitting in white grapefruit affected by GA3, grove (GR), or the interaction (GA3x GR) for March 18 and April 16 harvests. Grove 1 Grove 2 Grove 3 Significance Harvest date No GA 3 GA 3 No GA 3 GA 3 No GA 3 GA 3 GA 3 GR GA 3 xgr March * ** April ** Pitting incidence was defined as percent of fruit with at least 10 collapsed oil glands per fruit (n = 3 replicate boxes with 18 fruit per box). Factorial analysis was performed with GA 3 and grove as main treatments arranged in a randomized complete block. Significance is indicated as * and ** which represent confidence levels of 95 and 99%. 116