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INTRODUCTION
Salinity is a serious yield-limiting problem in arid and semi-arid regions (Arzani and Ashraf, 2016). For instance, Iran has an estimated salt affected land area of about 34 million ha that includes 4.1 million ha of irrigated land (FAO, 2000). Shortages of good quality water and population growth warrant provisions to extend agricultural production to marginal regions that contain saline water and soils (Arzani and Ashraf, 2016). Salinity causes a number of deleterious effects on plant growth and productivity such as water deficit due to low osmotic potential of soil solution and Na+ and Cl− specific ion toxicity, which disturbs metabolic function, cell membrane integrity and plant nutrition (Arzani, 2008; Arzani and Ashraf, 2016; Mansour, 2014; Negrao et al., 2017). A major target in most breeding projects is enhancing yield performance of crop plants grown in saline-affected areas (Arzani and Ashraf, 2016). Being a moderately salinity-tolerant crop species, melon (Cucumis melo L.) can be potentially cultivated in saline fields with variable yield penalties depending on genotype and severity of salinity stress (Botia et al., 2005; Huang et al., 2012; Tedeschi et al., 2011).
A number of reasons have been claimed for fruit yield losses due to salinity stress in melon; these include, but are not restricted to, decreases in plant water status, leaf Na+ accumulation and dramatic reductions in K+/Na+ ratio (Tedeschi et al., 2017). There is genotypic variation in salt tolerance of melon and irrigation with saline water decreased significantly both number of fruits and marketable yield while improving fruit quality (Botia et al., 2005). Under field conditions, the number of fruit per plant and the fruit weight were found to be the major fruit yield components affected by salinity stress (Huang et al., 2012; Tedeschi et al., 2011). In addition, the maintenance of K+ selectivity has been considered as a strategy for enhancing salinity tolerance and improving fruit quality in terms of total soluble solids (Tedeschi et al., 2011).
The present knowledge on the responses of melon cultivars to salinity stress under field condition is scant. Most field studies have concentrated on limited melon genotypes (Botia et al., 2005;...