Germination dynamics and growth responses under salinity stress in Thai water spinach (Ipomoea aquatica Forssk.)

Abstract:

This study investigated germination dynamics and early seedling responses of Thai water spinach (Ipomoea aquatica Forssk.) cultivars, ‘Khiao Sawoei’ and ‘Riao Phai’, under salinity levels ranging from 0 to 20 dS m^-1 in a controlled environment. Salinity primarily delayed germination timing rather than reducing final germination percentage. The experiment was conducted in a completely randomized design with two cultivars and six salinity levels, using three biological replicates per treatment. Each replicate contained 10 seeds, giving 30 seeds per cultivar × salinity treatment combination and 360 seeds in total. Increased salinity extended the lag phase, particularly at early stages 4 days after sowing (DAS), while final germination remained relatively high (73.33–96.67%) at 14 DAS across all treatments. In contrast, seedling growth was more sensitive to salinity. A statistically significant reduction (P < 0.05) in seedling dry weight and root length was first observed at 12 dS m^-1, despite high final germination (>80%). Between cultivars, differences in salinity responses were observed depending on the evaluated traits. ‘Riao Phai’ showed higher dry weight retention at 16 dS m^-1 at 14 DAS, whereas final germination percentage remained relatively stable in both cultivars. These findings indicate that salinity affects post-germination seedling growth more strongly than final germination, with 12 dS m^-1 representing a critical tested level for early growth inhibition in Thai water spinach.

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