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Title: Physiological and ionic changes in dwarf coconut seedlings irrigated with saline water

Author
item LIMA, BRENO - Federal Rural University Of Pernambuco
item LACERDA, CLAUDIVAN - Universidade Federal Do Ceara (UFC)
item NETO, MIGUEL - Federal Rural University Of The Semi-Arid
item Ferreira, Jorge
item BEZERRA, ANTONIO - Federal Rural University Of The Semi-Arid
item MARQUES, ELTON - Federal Rural University Of The Semi-Arid

Submitted to: Revista Brasileira de Engenharia Agricola e Ambiental
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2016
Publication Date: 1/5/2017
Citation: Lima, B.L., Lacerda, C.F., Neto, M.F., Ferreira, J.F., Bezerra, A.M., Marques, E.C. 2017. Physiological and ionic changes in dwarf coconut seedlings irrigated with saline water. Revista Brasileira de Engenharia Agricola e Ambiental. 21(2):122-127. doi: 10.1590/1807-1929/agriambi.v21n2p122-127.

Interpretive Summary: The consumption of coconut water has increased in recent years to accommodate the growing demand of consumers of natural hydrating drinks. Brazil is the fourth world producer of coconuts, but is the first world producer of coconut water with 80% of its planted area in the northeastern states. Besides drought, the Brazilian northeast is a semi-arid region afflicted by salinity of the soil, water, or both. Although the plant is fairly salt-tolerant once established, there is scarce information on the salt tolerance of coconut seedlings needed for maintaining and expanding the planted area in semi-arid regions to keep up with the growing demand for coconut water and other crop products (dry pulp, oil, milk, and fiber). The dwarf coconut palm has emerged as a precocious (fruits on average in 3.0 years), highly productive, and fairly salt-tolerant crop once established. However, little is known about the physiological and ionic changes that may contribute to the survival and establishment of seedlings under conditions of salinity. This study aimed to evaluate the effect of salinity of irrigation water on physiological and ionic parameters, and changes in compatible solubles in dwarf coconut seedlings. Although the concentration of chloride ions increased in both roots and leaves, concentration of sodium ions only increased in the leaves, allowing the plant to maintain leaf potassium for growth. However, chloride increased approximately three fold in leaves causing reductions in biomass accumulation 2.0-2.4 times more severe than in roots. The high levels of sodium and soluble solutes in cells of the roots, but not of shoots, suggest that roots play an important role in the mechanism of salt tolerance of coconut. Results suggest that chloride, not sodium, is the main toxic ion in coconut seedlings and that the canopy is more affected than roots. Seedlings were classified as tolerant up to 5.0 dS m-1 and moderately tolerant up to 10.0 dS m-1. These results indicate that using brackish water with ECw up to 5,0 dS m-1 allow for production of good quality seedlings of dwarf coconut. This knowledge is important for farmers in the semi-arid who rely on brackish water for their agricultural production of dwarf coconut and to save potable water for human and livestock consumption.

Technical Abstract: The use of salt-tolerant plants is an important alternative to cope with the problem of salinity in semi-arid regions. The dwarf coconut palm (Cocos nucifera L.) has emerged as a salt-tolerant crop once established. However, little is known about the physiological mechanisms that may contribute to the establishment of seedlings of this species under conditions of salinity. To increase the knowledge on seedling tolerance to salinity, this study aimed to evaluate the effect of salinity of irrigation water on physiological responses of dwarf coconut seedlings. The treatments consisted of five levels of salinity of irrigation water, which are expressed by the electric conductivity (ECw), as follows: S1 = 0.9 (control); S2 = 5.2; S3 = 10.1; S4 = 15.3 and S5 = 19.3 dS m/1. Although Cl- increased in both roots and leaves, Na+ only increased in the leaves, allowing the plant to absorb K+ at needed rates for growth. The high levels of organic solutes and Na+ in roots, in relation to the shoots, suggest that roots play an important role in the mechanism of salt tolerance of coconut. Our results clearly suggest the possibility of using brackish water with ECw up to 5,0 dS m/1 for production of seedlings of dwarf coconut, without reducing the quality of seedlings. Based on dry matter accumulation of roots and shoots, seedlings were classified as moderately tolerant to the salinity of 10 dS m/1.