Relationship between seed germination physiological characteristics and germination percentages of direct-seeded hybrid Indica rice under low-temperature and anaerobic interaction

Low-temperature and anaerobic conditions are two major limiting factors in the germination of direct-seeded rice. Sixteen hybrid Indica rice varieties were screened and subjected to two different temperatures and oxygen levels. The results revealed that relative to anaerobic conditons, low-temperature is the key limiting factor for seed germination. For all varieties, relative to normal temperature (30°C) and aerobic conditions (89.0% germination), the germination percentages when seeds were germinated under anaerobic (normal temperature), low-temperature (15°C) or combined anaerobic and low-temperature conditions were 64.0, 46.0 and 23.2%, respectively. Under the three latter treatments, the soluble sugar (SS) and gibberellin (GA) was significantly decreased, the abscisic acid (ABA) had significantly increased by 14.6–251.8%, and the superoxide dismutase (SOD) initially increased by 30.2–49.7% and decreased thereafter by 34.7%. Seeds of ‘Shen 9 you 28’ and ‘Jingliangyou 534’ performed better than seeds of the other varieties, with high germination percentages, SS, SOD, GA and low ABA. Correlation analysis revealed that the germination percentages were significantly correlated with the SS, SOD, GA, ABA and GA/ABA. Elevated SS, GA and SOD, as well as reduced ABA content were thought to account for the high germination of rice varieties resistant to combined low-temperature and anaerobic stress.