Kale (Brassica oleracea L. var. acephala DC) leaf water loss as affected by genotype and bagging

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1 ORIGINAL SCIENTIFIC PAPER Kale (Brassica oleracea L. var. acephala DC) leaf water loss as affected by genotype and bagging Gvozden Dumičić 1, Juan Carlos Díaz-Pérez 2, Harwinder Singh Sidhu 2, Branimir Urlić 1, Smiljana Goreta Ban 1, Dan MacLean 2, Sarah Workman 3 1 Institute for Adriatic Crops and Karst Reclamation, Split, Croatia, (gdumicic@krs.hr) 2 University of Georgia, Department of Horticulture, Tifton, Georgia, USA 3 University of Georgia, CAES Center for Agribusiness and Economic Development, Athens, Georgia, USA Abstract The aim of this study was to determine the effect of enclosing kale leaves in PE-bags on leaf weight loss, water loss rate and chlorophyll index in two kale genotypes (cv. Red Russian and Konavle 2 which is a Croatian local population). The experiment was consisted of six replications with three leaves per treatment at room temperature (22 o C; % RH) for five days. Non-bagged leaves of both genotypes, after 5 days, had more than %, while bagged leaves had only 17% of water loss. Water loss rate was higher in Red Russian than in Konavle 2 only in non-bagged leaves. Enclosing leaves in plastic bags reduced the rate of leaf water loss resulting in increased shelf life of kale leaves. Key words: chlorophyll index, leaf gas exchange, room temperature Introduction Kale is a native of the eastern Mediterranean, where it has been grown and used in the diet for more than 2,000 years (Balkaya and Yanmaz, 2005; Lešić et. al., 2004). Although a somewhat forgotten vegetable, in recent years kale has had increasing popularity as a result its high nutritional properties (Batelja et. al., 2009). Health benefits of kale can be compared to those of cabbage and savoy (Lešić et. al., 2004). Kale has the second strongest antioxidant activity against peroxyl radicals among 22 common vegetables, including spinach, broccoli, carrot and potato (Cao et. al., 1996). Kale leaf contains more than 85% of water (Lešić at. al., 2004). It is highly perishable after harvest and cannot be kept for more than a few days under ambient conditions of o C (Imungi, 1992). Retention of leaf colour, freshness and turgidity are factors that determine market value of kale. Methods used to reduce postharvest losses include cooling, waxing and packaging (Elkashif et. al, 1983). Tulio et. al. (2002) reported that jute leaves stored in polyethylene bags can be stored for extended periods. The aim of this study was to determine the effect of bagging on leaf weight loss, water loss rate and chlorophyll index of two kale genotypes stored at room temperature. Materials and methods Greenhouse grown seedlings of two kale genotypes [ Red Russian (Johnny s Selected Seeds, Winslow, Maine. USA) and Croatian local population Konavle 2 ] were planted in the field on 13 March 2011 at the Horticulture Farm, Univ. of Georgia, Tifton (31 o 28 N; 83 o 31 E), GA, USA. Preharvest leaf gas exchange. Leaf gas exchange was measured in the field the day before harvest with a photosynthesis system (LI-, Li-Cor, Lincoln, NE, USA). Postharvest leaf weight loss, water loss rate, and chlorophyll index. Six marketable leaves (fully expanded and free from damage) per each replication were harvested on 2 June 2011 between 8:00 and 8:30am, kept in an ice chest, and immediately transported to the laboratory 49. hrvatski i 9. međunarodni simpozij agronoma Dubrovnik Hrvatska 305

2 Vegetable Growing, Ornamental, Aromatic and Medicinal Plants [Vidalia Onion Research Lab (VORL), Tifton, GA]. We used Clarke and McCaig (1982) procedure, with the following modifications. Leaf petioles were recut to have leaf petioles of about the same size. The experiment consisted of six replications with three leaves per treatment [(treatment = genotype ('Konavle 2' or 'Red Russian') x bagging (bagged or nonbagged)]. For the bagging, leaves were enclosed inside a 15 L volume polyethylene (PE) bag (Berry plastics corporation Evansville, Indiana). Both bagged and non-bagged leaves were kept at room temperature (22 o C; % RH) for five days. Leaf weight loss (WL) and water loss rate (WLR) were calculated by measuring daily changes in leaf fresh weight for five days, as follows: WL (%) = [(Wo - Wn)/(Wo *100)] WLR (%/day) = ((Wo-Wn)/((t)*(Wo)))*100, where are Wo-initial weight, Wn-weight at period n, tn-time between two measurements. Leaves were weighed at 0 (immediately after arrival to the laboratory), 5, 24, 48, 72, 96 and 120 h after harvest. On each weighing period, immediately after leaf weight determination, leaf chlorophyll index (an estimator of leaf greenness) was determined at four points on the upper one third of each leaf with a handheld chlorophyll meter (SPAD 2, Konica Minolta, Minolta Corp, Ramsey, N.J.). After the 5 day period, leaves were oven-dried at 75 o C for 48 h to determine leaf dry weight. Statistical Analysis Data were analyzed by analysis of variance (ANOVA), using StatView statistical software (StatView for Windows; SAS Institute Inc. Copyright ; Version 5.0). Following a significant F-test, means were separated using the LSD-test at P Results and discussion Preharvest leaf gas exchange. All leaf gas exchange factors: photosynthetic rate, stomatal conductance, intercellular CO2 and transpiration were significantly higher in Konavle 2 than in Red Russian' (Table 1), probably because Konavle 2 is more tolerant to heat stress conditions compared to Red Russian. Konavle 2 has been selected by farmers for its tolerance to drought and poor soil conditions. On cabbage seedlings, Sato et al. (2004) were reported by that photosynthetic rate was lower in stressed than in non-stressed plants. Table 1. Leaf gas exchange: photosynthetic rate (A), stomatal conductance (gsw), intercellular CO2 (Ci) and transpiration (E), of two kale genotypes Konavle 2 and Red Russian grown in the field and measured the day before harvest (2 June 2011). Tifton, Georgia, USA. Gas exchange variables Cultivar A (μmol m -2 s -1 ) g sw (mol m -2 s -1 ) C i (μmol mol -1 ) E(mmol H 2O m -2 s -1 ) Konavle ±1.55 a 0.49± ± ±0.47 Red Russian 27.2± ± ± ±0.63 P < a Values are presented as mean value ±SD (n =6). Postharvest leaf weight loss, water loss rate, and chlorophyll index. Leaf weight loss was higher in unbagged than in bagged leaves (Fig. 1). By day 5, non-bagged leaves of both genotypes had more than % WL, while bagged leaves had only 17% WL. Leaf weight loss in non-bagged leaves was higher in 'Red Russian' than in 'Konavle 2'. There was no difference in WL between genotypes of bagged leaves. Our results are consistent with those of Elkashif et.al. (1983) showing that polyethylene film significantly reduced WL in broccoli th Croatian & 9 th International Symposium on Agriculture Dubrovnik Croatia

3 L e a f w e i g h t l o s s (%) T i m e ( h o u r s) Graph 1. Postharvest leaf weight loss (% of initial weight) of kale genotypes Konavle 2 and Red Russian as a function of time after harvest and as affected by leaf bagging. Leaves were kept room temperature (22 o C; % RH). Vertical bar indicates mean ±1 SE. Water loss rate declined with time after harvest (Fig. 2). This decline, however, was more accentuated in unbagged compared to bagged leaves, irrespective of genotype. A decreased WLR with increased time after harvest has also been reported in bell pepper (Díaz-Pérez et al., 2007). Water loss rate showed significant genotype x bagging interaction. WLR was higher in Red Russian than in Konavle 2 only in non-bagged leaves. Although Red Russian leaves had significantly lower stomatal conductance and transpiration than Konavle 2, Konavle 2 probably acclimated better to suboptimal conditions. Denna (1970) found that most of water loss in cabbage leaves in daytime experiments was through stomatal transpiration. Increased WLR of Red Russian might be result of poor adaptation traits including slower closing of stomata in the first 24 h after harvest. Dahanda and Sethi (1998) report that genotype-environment interactions significantly affected excised-leaf water loss in bread wheat. The increased WLR of Red Russian may also be attributed to an increased leaf cuticular conductance. Chlorophyll index remained about constant for the first 48 h after harvest and then decreased with time after harvest in all treatments (Fig. 3), which is consistent with the observed decreased leaf greenness (increased yellowing) with time after harvest. A similar decreased greenness after 48 h was reported by Pogson and Morris (1997) in broccoli. In unbagged leaves, CI was higher for Red Russian than for Konavle 2. In contrast, in bagged leaves, Red Russian showed a decreased CI compared to all the other treatments. This decreased CI in unbagged leaves of Red Russian was possibly caused by an increased ethylene concentration inside the bag and suggests that the two genotypes differ in sensitivity to ethylene. 49. hrvatski i 9. međunarodni simpozij agronoma Dubrovnik Hrvatska 307

4 Vegetable Growing, Ornamental, Aromatic and Medicinal Plants W a t e r l o s s r a t e (% / d a y) T i m e ( h o u r s ) Graph 2. Postharvest leaf water loss rate (% day -1 ) of kale genotypes Konavle 2 and Red Russian as affected by leaf bagging at room temperature (temperature = 22 o C; RH %). Vertical bar indicates mean ±1 SE. C h l o r o p h y l l i n d e x Graph 3. Chlorophyll index concentration of kale genotypes Konavle 2 and Red Russian as affected by bagging at room temperature (temperature = 22 o C; RH %) in Tifton GA. Vertical bar indicates mean ±1 SE. Conclusions T i m e ( h o u r s ) Kale showed a high water loss rate and loss of greenness at room temperature. Kale genotypes differed in rates of leaf water loss and greenness after harvest. Enclosing leaves in plastic bags reduced the rate of leaf water loss resulting in increased shelf life of kale leaves th Croatian & 9 th International Symposium on Agriculture Dubrovnik Croatia

5 Acknowledgements This paper was done as part of the project "Croatia Agriculture Research and Education Exchange" funded by the USDA ISE (Grant: ). References Balkaya A. and Yanmaz R. (2005). Promising kale (Brassica oleracea L. var. acephala) populations from Black Sea region, Turkey. New Zeland Journal of Crop and Horticultural Science. 33: 1-7. Batelja K., Goreta Ban S., Žanić K., Miloš B., Dumičić G., Matotan Z. (2009). Autochthonous kale populations (Brassica oleracea L. var. acephala) in Croatian coastal region. Agriculture 2: 1-7. Clarke J.M., and McCaig T.N. (1982). Excised-leaf water retention capability as an indicator of drought resistance of Triticum genotypes. Canadian Journal of Plant Science. 62: Cao, G., Sofic, E., & Prior, R. L. (1996). Antioxidant capacity of tea and common vegetables. Journal of Agricultural and Food Chemistry. 44: Denna D. W. (1970). Transpiration and the waxy bloom in Brassica oleracea L. Australian. Journal of Biological Sciences. 23: Dhanda S.S. & Sethi G.S. (1998). Inheritance of excised-leaf water loss and relative water content in bread wheat (Triticum aestivum). Euphytica 104: Díaz-Pérez, J.C., M.D. Muy-Rangel, and A.G. Mascorro Fruit size and stage of ripeness affect postharvest water loss in bell pepper fruit (Capsicum annuum L.). Journal of the Science of Food and Agriculture. 87: Elkashif M. E., Huber D. J., and Sherman M. (1983). Delaying deterioration of broccoli and cucumber using polymeric films. Proceedings Florida State Horticultural Society. 96: Imungi, J. K. (1992). Postharvest handling of perishable crops. In Proceedings of the postharvest management of food crops seminar held in Serena hotel. Nairobi: Jomo Kenyatta University of Agriculture and Technology. Lešić R., Borošić J., Buturac I., Herak-Ćustić M., Poljak M., Romić D. (2004) Povrćarstvo. Zrinski, Čakovec. Pogson B.J., Morris S.C. (1997). Consequences of cool storage of broccoli on physiological and biochemical changes and subsequent senescence at 20 C. Journal of the American Society for Horticultural Science. 122: Sato F., Yoshioka H., Fujiwara T., Higashio H., Uragami A, Tokuda S. (2004). Physiological responses of cabbage plug seedlings to water stress during low- temperature storage in darkness. Scientia Horticulturae 101: Tulio Jr A.Z., Ose K., Chachin K., Ueda Y. (2002) Effects of storage temperatures on the postharvest quality of jute leaves (Corchorus olitorius L.). Postharvest Biology and Technology. 26: hrvatski i 9. međunarodni simpozij agronoma Dubrovnik Hrvatska 309

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