Morphological and physiological responses of Thai commercial pummelo cultivars under salt stress

Pummelo production in the lower central region of Thailand, especially in Nakhon Prathom province, has been affected by the high sea bolster during the dry season. The sea water rising of each area decreased tree growth, induced leaf burn, induced shoot dieback and tree death. Also salt accumulation caused saline soil problems. There is still lacking information of pummelo tolerance to salinity levels especially in commercial pummelo cultivars included ‘Thongdee’ and ‘Khaonamphueng’. The objective of this study was to evaluate morphological (shoot extension, shoot fresh and dry weights, leaf area, leaf number, leaf burn, root fresh, and dry weights) and physiological (photosynthesis rate, transpiration, leaf greenness, leaf water potential, and relative water content) parameters related to salt stress. The completely randomized design with 4 levels of salt concentrations; 2, 4, 8, and 16 ds m^‑1 were applied by using Hoagland’s nutrient solution for 13 weeks to 4-month-old shoot layering of ‘Thongdee’ and ‘Khaonamphueng’ cultivars. In addition, orthogonal comparison was used to predict the significant response to salinity effects of those pummelo cultivars. The results showed that salt stress caused leaf burn in both of ‘Thongdee’ (>8 dS m^‑1) and ‘Khaonamphueng’ (16 dS m^‑1). In ‘Khaonamphueng’, salt stress caused quadratic decrease in shoot fresh weight, shoot dry weight, leaf area, root fresh weight, root dry weight and leaf water potential and linear decrease in photosynthesis rate. For ‘Thongdee’, salt stress caused quadratic decrease in all parameters. Meanwhile, leaf greenness was not significantly different. Comparing salt tolerance between two cultivars, ‘Khaonamphueng’ was more resistant to salinity than ‘Thongdee’.