**Yu-Syuan Li, Shang-Ling Ou and Chin-Ying Yang \***

Department of Agronomy, National Chung Hsing University, Taichung 40227, Taiwan; shaneimayday@gmail.com (Y.-S.L.); slou@dragon.nchu.edu.tw (S.-L.O.)

**\*** Correspondence: emiyang@dragon.nchu.edu.tw; Tel.: +886-4-22840777 (ext. 608); Fax: +886-4-22877054

Received: 17 July 2020; Accepted: 1 August 2020; Published: 3 August 2020

**Abstract:** *Oryza sativa* is a major food crop in Asia. In recent years, typhoons and sudden downpours have caused field flooding, which has resulted in serious harm to the production of rice. In this study, our data revealed that the plant heights of the five *Japonica* varieties increased during submergence. The elongation rates of TN14, KH139, and TK9 increased significantly during submergence. Chlorophyll contents of the five varieties significantly decreased after submergence and increased after recovery. Moreover, the chlorophyll content of KH139 was significantly higher than those of the other four varieties after recovery. The plant survival rates of the five varieties were higher than 50% after four-day submergence. After eight-day submergence, the survival rate of KH139 remained at 90%, which was the highest among the different varieties. The KH139 presented lower accumulation of hydrogen peroxide and the catalase activity than those of the other four varieties under submergence. The *sucrose synthase 1* and *alcohol dehydrogenase 1* were induced in KH139 under submergence. The results presented that different varieties of *japonica* rice have different flood tolerances, especially KH139 under submergence was superior to that of the other four varieties. These results can provide crucial information for future research on *japonica* rice under flooding stress.

**Keywords:** *Oryza sativa*; Submergence; Activity of antioxidant enzymes; Chlorophyll content
