Journal of Food, Agriculture & Environment, Vol.12 (2), April 2014 307 www.world-food.net Journal of Food, Agriculture & Environment Vol.12 (2): 307-313. 2014 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Received 5 January 2014, accepted 18 March 2014. Growth performance and ionic composition of Chinese kale (Brassica oleracea var. alboglabra L.) plants grown under saline conditions Amin Tayebi-Meigooni, Yahya Awang *, Adam Puteh, Babak Madani and Amirmahdi Khalatbari Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia. e-mail: amin_ir@hotmail.com, yahya_awg@putra.upm.edu.my Abstract In order to assess the changes in growth and ionic composition of the Chinese kale (Brassica oleracea var. alboglabra) plants under salinity, a greenhouse experiment was conducted. Three-week-old plants were installed in hydroponic with varying concentrations of NaCl (0, 25, 50, 75 and 100 mM) for two weeks. The growth indices including leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) besides nutrient composition in both leaf and root tissues were estimated. Increasing salinity level (>25 mM) in root zone negatively affected plant growth. The effects were identified using variation in growth indices through hyperosmotic pressure and ion toxicity at early and mid/final stages of salinity, respectively. The preliminary changes depicted over correspondingly reduced LAR and NAR, which diminished RGR at beginning of imposing salinity. The secondary RGR reduction mainly attributed with suppression of NAR at moderate salinity level (50 mM), and concomitance of both NAR and LAR inhibition for higher salinity (75 and 100 mM) at the end of experiment. Increasing the level of Na and Cl adversely affected plant K, Ca, Mg and N content in both leaf and root tissues. Despite leaf P content, salinity induced root P to the point, which may be hazardous to root cells. Reduction of N and Mg availability for various processes such as chlorophyll biosynthesis, phosphorus shortage in bioenergetic pathway, besides imbalance of K and Ca and negative effects of Na and Cl to different bioactive processes were also considered to be responsible for growth reduction in this plant. Key words: Growth analysis, leaf area ratio, relative growth rate, net assimilation rate, crop growth rate, sodium, potassium, calcium, magnesium, chloride, phosphorus, nitrogen. Introduction Salinity is a major constraint to crop production worldwide. Salinity affects plant growth and development through osmotic and ionic stresses, and it is directly dependent on the total concentration of soluble salts and osmotic potential of the root medium 1, 2 . Decrease in the cell enlargement and leaf elongation velocity due to osmotic stress implies less photosynthetic surface, that results in low plant growth and developmental performance 3, 4 . Increasing the toxic ions Na + and Cl - in plant tissues cause restriction in uptake of K + , Ca 2+ and Mg 2+ 5-7 . Competition of Na + with K + and inhibitory effects on Ca 2+ uptake and transport were considered as the negative effects of Na + to essential cations 6, 8, 9 . It has been also argued that salinity has a negative interference on the nitrogen and phosphorus acquisition and utilization 10-12 . These effects are orchestrated by antagonistic effects of Cl - and results in reduction of plant biomass production 13 . Ionic cytotoxicity has shown to be the predominant cause of crop susceptibility due to replacement of Na + instead of K + and binding of Na + and Cl - ions with amino acids 14 , which generally causes inhibition of plant growth and development through disruption of major metabolic functions includes photosynthesis, respiration, protein synthesis and nucleic acid metabolism 15 . Growth analysis is a fundamental tool to characterize plant responses to environmental stress and provides useful information on defining when stress occurs and also for a critical analysis of series of events leading to growth inhibition 16 . Using this information, attribution of interspecific differences in salt tolerance with morphological changes or photosynthetic responses can be clarified. Changes in relative growth rate (RGR) with time can be detected and correlated with two variables including net assimilation rate (NAR) and leaf area ratio (LAR) 16 . Hence, RGR fluctuation can be explained by variation in NAR and LAR. Chinese kale originally is a Chinese vegetable belonging to the Brassicaceae family and is eaten as fresh and/or cooked daily for human food. Chinese kale is usually grown for its bolting stems as the common edible part. Recent researches indicate that Chinese kale offers unique nourishment due to its rich source of glucosinolates and ascorbic acid 17, 18 . There is no record available for the growth and ion accumulation of Chinese kale in response to saline conditions. However, salt-tolerance definition from horticultural perspective is mainly based on the yield of the harvestable organs. Understanding how salinity affects vegetative development of Chinese kale is important for developing management strategies to alleviate the stress effect at critical times on plant growth and development. Hence, this study was conducted to analyse changes in morphological characteristics and nutrient composition in B. oleracea var. alboglabra grown under saline conditions. Information on nutritional imbalance that may be induced under saline environment would be beneficial especially in the formulation and application of fertilizer for crops. Materials and Methods Plant material and growth condition: The seeds of Brassica oleracea var. alboglabra cv. ‘Standard kailan’ were obtained from local supplier. The seeds were sown in trays maintained with water spray until seedling emergence. Young seedlings in the seed trays