Effects of Selenium on Growth Parameters of Tomato and Basil
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HORTSCIENCE 51(8):1050–1056. 2016. Se has been recognized as an essential trace element for animals and humans (Oldfield, 2002). Adult humans have a daily requirement Effects of Selenium on Growth of 55 to 70 mg Se. Se-deficiency diseases have been recognized in some regions: Keshan Parameters of Tomato and Basil under disease, an endemic cardiomyopathy, and Kashin–Beck disease, a deforming arthritis, Fertigation Management were first identified in the Keshan region of China, where the soil is extremely low in Se Menahem Edelstein1 (Chen et al., 1980; Tan and Huang, 1991). Department of Vegetable Crops, Newe Ya’ar Research Center, Agricultural Diet is the main source of Se for humans Research Organization, Ramat Yishay, Israel and animals. Therefore, increasing Se con- centrations in the tissues of edible crops by Daniel Berstein Se-fertilization strategies would improve Department of Vegetable Crops, Newe Ya’ar Research Center, Agricultural the overall contribution of Se to human and animal diets (Carvalho et al., 2003). Research Organization, Ramat Yishay, Israel; and Department of Soil and Plants play a unique role in recycling and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and delivering Se from the soil into the food Environment, The Hebrew University of Jerusalem, Israel chain, even though Se has not been yet confirmed as an essential plant micronutrient. Moshe Shenker In Finland, for example, selenate has been Department of Soil and Water Sciences, The Robert H. Smith Faculty of added to fertilizers since 1984 to increase the Agriculture, Food and Environment, The Hebrew University of Jerusalem, Israel Se in soils (Alfthan et al., 2010; Wang et al., 1998), where the geochemical soil conditions Hasan Azaizeh are relatively uniform, two decades of sup- Institute of Applied Research (Affiliated with University of Haifa), the Galilee plementation of soils nationwide with fertil- Society, P.O. Box 437, Shefa-Amr 20200, Israel; and Tel Hai College, Upper izers containing inorganic Se were safe and effective way of significantly increasing Se Galilee 12210, Israel concentrations in most crop plants grown for Meni Ben-Hur human consumption (Alfthan et al., 2010). Great Britain has also undertaken efforts to Institute of Soil, Water and Environmental Sciences, Volcani Center, Bet-Dagan, develop soil amendment practices with in- Israel organic Se to increase dietary Se intake Additional index words. Ocimum basilicum, selenium bioaccumulation, selenium fortification, through the Se biofortification of food crops (Rayman, 2012). Similarly, vegetables rich in selenium phytotoxicity, Solanum lycopersicum Se contribute as much as 28% to 32% of Abstract. Tomato ‘Abigail’ (Solanum lycopersicum L.) and basil ‘Perry’ (Ocimum basilicum humans’ daily Se intake in northern Mexico L.) were selected as model plants for selenium (Se) supplementation to evaluate a) effects of (Kopsell et al., 2009). Malorgio et al. (2009) Se concentration in nutrient solution on Se content in different organs under fertigation, investigated the effects of Se fertilizer in a b) Se phytotoxicity threshold values, and c) mechanisms. Plants grown in a glasshouse were hydroponic system on growth of lettuce and irrigated with 0, 1, 2, 5, and 10 mg Se/L in the first experiment, while with 0, 0.25, 0.5, 0.75, chicory and Se content in the plant tissues. 1.0, and 1.5 mg Se/L in the second. Tomato plants accumulated Se linearly with rising Se Addition of 0.5 and 1.0 mg·L–1 Se in the concentrations, whereas accumulation in basil followed a saturation curve. Plants nutrient solution had a positive effect on plant supplemented with 1.5 mg Se/L in the irrigation water accumulated 0.23 and 0.88 mg yield and increased Se content in the crops’ Se/g dry weight (DW) in tomato fruits and basil shoots, respectively. However, tomato leaves. Kopsell et al. (2009) reported a linear roots, shoots and fruits DW were 56%, 36%, and 66% lower than in controls, respectively, accumulation of Se up to 56 mg·kg–1 in leaves and basil roots and shoots DW were 92% and 88% lower than in control, respectively. of basil after foliar fertilization with three Calculated toxicity-threshold values were 1.27 mg Se/L for tomato and 0.44 mg Se/L for applications of 32 mg·L–1 Se. In that study, basil. Tomato crops were more tolerant than basil crops, although data suggested yield daily Se application in the irrigation system reduction at lower Se concentrations than those effecting biomass reductions. The results seemed to be more efficient than foliar indicate that Se supplementation through drip irrigation may efficiently fortify tomato and application. basil. However, Se concentrations should be lower than 0.75 and 0.25 mg·LL1 for tomato Contrary various industrial activities, such and basil, respectively, to avoid yield reduction and possible Se phytotoxicity. as oil refineries, electrical utilities, and waste from glass, synthetic pigments, and semicon- ductor devices can contaminate soil and water Selenium is a nonmetal element belong- that form the earth’s crust. Se is found in bodies with Se (Mirbagheri et al., 2008; Terry ing to the oxygen–sulfur–tellurium group, sulfide ores such as pyrite, where it partially et al., 2000). In addition, irrigation of semiarid and is ranked 70th among the 98 elements replaces the sulfur. Oxidation of pyritic parent farmlands in seleniferous regions is a common material is an important natural source of Se source of Se contamination, particularly in the in soil where human activities, such as presence of an impermeable subsurface layer, Received for publication 17 May 2016. Accepted mining, groundwater drawdown, and wet- where leached Se can accumulate to toxic for publication 15 June 2016. land drainage, have exposed pyritic mate- levels. This phenomenon has been well docu- We would like to thank Lea Leib, Irit Levkovitch, rials to a more oxidizing environment (Strawn mented in the San Joaquin Valley of Cal- and Fares Halahlih for their valuable technical et al., 2002). Se content in most soils ranges ifornia, where high concentrations of Se assistance in the chemical analysis; Fabian Baumkoler from 0.01 to 2 mg·kg–1, but can vary from (300 mg·L–1) in the subsurface agricultural and Uzi Saar for technical assistance in the glass- 0 to >10 mg·kg–1 in certain regions (Fordyce, drainage water caused a high incidence of house experiments; and Raanan Asor from Mekorot, Israel’s national water company. Contribution No. 2005). Se is distributed in the environment deformity and mortality in waterfowl hatch- 2/2016 from the Agricultural Research Organiza- through natural processes of weathering; dis- lings at the Kesterson National Wildlife Refuge tion, the Volcani Center, Bet Dagan, Israel. posal of human, animal, and plant wastes; (Deverel and Millard, 1988; Fio et al., 1991; 1Corresponding author. E-mail: medelst@volcani. and emission of volcanic ash (Oldfield, Fujii et al., 1988; Ohlendorf et al., 1986; agri.gov.il. 2002). Spallholz and Hoffman, 2002). Anthropogenic 1050 HORTSCIENCE VOL. 51(8) AUGUST 2016 Se contamination of groundwater was docu- mented in the Shimron wells located in the Yizre’el Valley in northern Israel (Michelson, 1990). A high concentration of Se (up to 37 mg·L–1) in the well water caused shut- down of two wells in the surrounding area (Michelson, 1990). This high Se concentra- tion could enter the food chain and injure humans and animals. In humans, daily intake greater than 900 mg Se may result in toxicity, termed selenosis (Kopsell et al., 2009). Plants accumulate selenate against its electrochemical potential gradient by active transport. Among the factors that affect Se status in the plant, species is the most important. Plants can be classified into three main groups according to their Se uptake: primary, secondary, and non-Se accumula- tors. The Se toxicity threshold for nonaccu- mulator plants varies from 2 to 330 mg·kg–1 DW in rice and white clover, respectively (Terry et al., 2000). In contrast, Se-accumulator plants can hold Se concentrations of >4000 mg·kg–1 with no toxic effects (Terry et al., 2000). Beath et al. (1937) found a Se level of 14,990 ppm in a sample of Astragalus race- mosus, which is a primary accumulator. Also, most plants, even when grown in seleniferous soils, only contain 10 ppm Se, or less. Se can accumulate in plant tissues to levels that are toxic to the plant itself. In this case, high Se contents in the plant tissue can cause growth inhibition, yield reduction, chlorosis, and even plant mortality (Terry et al., 2000). Hurd-Karrer (1937) was the first to describe Fig. 1. Leaf damage to basil (upper row) and tomato (lower row) in response to selenium (Se) concentration Se phytotoxicity (snow-white chlorosis) in (0, 1, 2, and 5 mg Se/L) in nutrition solution. wheat plants that were exposed to 20 mg Se/kg soil in a pot experiment. Se phytotoxicity in wheat was also investigated under field, glasshouse, and laboratory conditions by Lyons et al. (2005), In that study, no Se toxicity symptoms were observed in the field trials with rates of up to 120 g Se/ha as selenate, and in pilot trials with up to 500 g Se/ha applied to the soil or up to 330 g Se/ha applied to the foliage, with soils containing low sulfur (S) concentrations (2–5 mg·kg–1). The critical tissue level for Se toxicity was 325 mg·kg–1 on a DW basis, attained by adding 2.6mgSe/kgtothegrowthmediumasselenate. Solution concentrations above 10 mg Se/L inhibited early root growth of wheat in labo- ratory studies (Lyons et al., 2005). The narrow margin between beneficial and harmful levels of Se has important implications for human health and crop pro- duction.