Effects of Daily Harvest Time on Postharvest Longevity, Water Relations, and Carbohydrate Status of Selected Specialty Cut Flowers

Effects of harvest time (morning, noon, or afternoon) on water uptake, fresh weight changes, termination symptoms, leaf relative water content (LRWC), carbohydrate status, and vase life of cut ‘ABC Purple’ lisianthus (Eustoma grandiflorum Salisb.), ‘Double Eagle’ African Gold Coin Series marigold (Tagetes erecta L.), and ‘Deep Red’ Benary’s Giant Series zinnia (Zinnia elegans Jacq.) were studied. For stems of lisianthus harvested and then stored in the dark with the basal ends in water for 2 weeks at 3 ± 1 8C, those harvested at noon (1200 HR to 1300 HR) or in the afternoon (1700 HR to 1800 HR) had longer vase life compared with stems harvested in the morning (0700 HR to 0800 HR). However, stems of lisianthus evaluated without storage had no differences in vase life. Stems of marigold harvested in the afternoon had longer vase life than morningor noonharvested stems. Time of harvest had no effect on cut flower longevity of zinnia. However, vase life was considerably shorter for stems of all species when tested after 2 weeks storage compared with freshly harvested stems. Stems of zinnia harvested at noon had lower LRWC than morningor afternoon-harvested stems. Marigold stems harvested in the afternoon and evaluated without storage had lowest LRWC on Day 7 of vase life. Harvest time or storage did not influence LRWC of lisianthus. Stems of marigold and lisianthus harvested at noon or in the afternoon had higher levels of carbohydrates compared with morning-harvested stems, whereas freshly harvested stems had higher concentrations of glucose and sucrose, which decreased during storage or the vase period. Sucrose concentrations varied more significantly among various tissues than other sugars presumably as a result of translocation during vase life. In summary, carbohydrate status of stems harvested at different times of the day varied greatly and affected postharvest longevity of cut marigold and lisianthus, but not zinnia. Many post-production factors affect vase life of cut flowers including developmental stage at harvest, temperature during the vase period, water loss, and various aspects of the vase solution such as sucrose levels, microbial populations, pH, electrical conductivity (EC), and overall water quality (Sacalis, 1993). To maintain flower quality, studies have focused on storage (Ahmad et al., 2012; Cxelikel and Reid, 2002; Jones et al., 2004), floral preservatives (Doi and Reid, 1995; Elhindi, 2012; Gast, 1997), or use of ethylene inhibitors, e.g., silver thiosulfate and 1methylcyclopropene (Blankenship and Dole, 2003; Chamani et al., 2005), nano-silver (Kim et al., 2005; Liu et al., 2012), and other commercial antiethylene agents (Staby et al., 1993). However, postharvest longevity of cut flowers is also affected by a variety of both preharvest (e.g., harvest season, solar radiation, temperature, relative humidity, water, and mineral nutrient stress) (Halevy and Mayak, 1979; Reid and Jiang, 2012; Slootweg, 2005) and postharvest (e.g., harvest stage, harvest procedures, ethylene, vase water quality, preservatives, storage method and duration, etc.) factors (Halevy and Mayak, 1981; Marissen and Benninga, 2001; van Doorn, 2012). In addition to the aforementioned factors, the time of the day when stems are harvested may be a potentially important consideration (Clarkson et al., 2005; Hasperué et al., 2011; Rapaka et al., 2007). Generally, stems are harvested by growers in the morning allowing more time for processing and marketing and to avoid field heat, which preserves quality and minimizes transpiration and thereby desiccation. However, for many species, morning harvest may not be the proper time because many plant physiological processes change diurnally and can affect postharvest longevity of cut stems. For instance, diurnal variations in ascorbic acid levels of spinach (Spinacea oleracea L.) (Kiyota et al., 2006) and chlorophyll precursors in bean (Phaseolus vulgaris L.) (ArgyroudiAkoyunoglou and Prombona, 1996) have been reported. However, the most pronounced effect of diurnal fluctuations has been observed on carbohydrate metabolism in plants (Hasperué et al., 2011). Changes in solar radiation greatly affect endogenous carbohydrate reserves, which accumulate during the day and are remobilized by the end of the dark period (Sicher et al., 1984). Harvesting later in the day compared with morning harvesting increased shelf life considerably for leaves of basil (Ocimum basilicum L.) (Lange and Cameron, 1994), baby salad [Eruca vesicaria (L.) ssp. Sativa (Mill.)] Thell. (Clarkson et al., 2005), and unrooted shoot-tip cuttings of lantana (Lantana comara L.) (Rapaka et al., 2007). These variations in shelf life were attributed to varying carbohydrate levels and diurnal changes in plant metabolic processes. Genotype and environmental conditions can also impact postharvest longevity. Cultivars of lettuce (Lactuca sativa L.) harvested at different times during the day have varying postharvest quality (Moccia et al., 1998). Butterhead lettuce had the best quality when harvested later in the day, whereas Latin-type lettuce had the best quality when harvested in early morning. Moreover, fluctuations in carbohydrate levels of field-grown crisphead lettuce have been observed between morning and afternoon harvests (Forney and Austin, 1988). Crisphead lettuce harvested in the afternoon had higher sucrose than morning harvests, whereas glucose and fructose were greater in morning harvests. Soluble sugars like sucrose act as signaling molecules for plants under stress and move between cells causing fluctuations in sugar concentrations during senescence (Chuang and Chang, 2013). Moreover, sucrose application reduced ethylene responsiveness in florets of broccoli (Brassica oleracea L.) and carnation (Dianthus caryophyllus L.) flowers (Nishikawa et al., 2005; Verlinden and Garcia, 2004). These diurnal plant carbohydrate changes can greatly affect postharvest longevity of cut flowers. However, limited information is available on the effects of time of harvest on extending postharvest performance (vase life) of particular ornamental crops. Therefore, Received for publication 13 Nov. 2013. Accepted for publication 27 Dec. 2013. This research was funded in part by the North Carolina Agricultural Research Service (NCARS), Raleigh, NC. Use of trade names in this publication does not imply endorsement by the NCARS of products named nor criticism of similar ones not mentioned. We thank John D. Williamson for critically reviewing the manuscript and Weiwen Guo for technical assistance with carbohydrate analysis. We are also grateful to the Endowment Fund Secretariat, University of Agriculture, Faisalabad, Pakistan, for financial support of the senior author. Postdoc Scholar. Professor and Head. Alumni Distinguished Graduate Professor Emeritus. To whom reprint requests should be addressed; e-mail iftikharahmadhashmi@gmail.com, iahmad3@ ncsu.edu. HORTSCIENCE VOL. 49(3) MARCH 2014 297 | POSTHARVEST BIOLOGY AND TECHNOLOGY