We have previously reported the sugar distribution and accumulation in watermelon fruit grown hydroponically (Tomiyama et al. 2023 . Hort Science). In this research, the contents of amino acids and mineral in watermelon fruits grown hydroponically at high concentrated nutrient solution were investigated. Three different hydroponic culture conditions were set by Electric Conductivity: EC 5.0, 3.0, and 1.2 dS-m-¹. Initially watermelon seedlings (Citrullus lanatus (Thunb.) Matsum. Et Nakai ‛Hitorijime-BonBon) were grown at EC 1.2 dS-m-¹ (Control) conditions on deep flow technique in a glasshouse. Treatment was initiated two weeks after pollination. Forty days after pollination, watermelon fruits were harvested and measured its size. Then, mineral and amino acids content were analyzed by HPLC. We measured NH⁴⁺, K⁺, Mg⁺, and Ca²⁺ as cations and PO⁴- and NO³- as anions. Twenty amino acids were measured also. As result, the fruit size and weight decreased under high nutrient conditions. At mineral analysis, the cations NH⁴⁺, Mg⁺, and Ca²⁺ content in the flesh did not increase at the high concentrated treatment, but K⁺ increased in the pericarp at higher treatment. Similarly, the anions PO⁴- and NO³- content increased as K⁺. In control, amino acids was accumulated in the center of flesh, whereas in the higher concentration amino acids was concentrated in the pericarp. When we focused on citrulline and proline, they were accumulated more in pericarp than flesh. In conclusion, mineral (K⁺, PO₄³-, NO₃-)and some amino acids such as citrulline, and proline, which accumulate in the pericarp, accumulated under high concentrated liquid fertilizer at hydroponic culture.
