Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice

Previous studies have shown that selenium (Se) can influence rice growth and yield. However, the Se effect on rice lodging remains unknown. This study aimed to investigate the impact of different Se treatments on seedling growth and stem sheath hardness in fragrant rice. A hydroponic experiment was conducted using two fragrant rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, as experimental materials. Two forms of selenium fertilizers (amino acid-chelated selenium and sodium selenite) were used. There were five foliar spraying selenium fertilizer treatments (CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; and T4: 8 μmol·L−1 sodium selenite), and the effects of the different selenium fertilizer treatments on seedling growth and stem sheath hardness in fragrant rice were studied. Significant Se treatment effects on root fresh weight, seedling dry weight, plant height, stem sheath length, number of leaves, chlorophyll content, stem sheath hardness, peroxidase activity in leaf and stem sheaths, and lignin content in the roots were detected. A significant Se treatment and variety interaction effect on the stem sheath hardness was observed. The different forms/levels of selenium fertilizer affected the seedling growth and the stem sheath hardness differed. The Se treatments improved seedling growth and significantly affected the dry weight, chlorophyll content, stem sheath hardness, and peroxidase activity in leaf and stem sheaths. Compared with the CK treatment, the Se treatments increased the total dry weight of seedlings in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 25.43–52.77% and 18.97–30.09%, respectively. The T2–T4 treatments increased the stem sheath hardness values in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 21.6–54.7% and 38.3–146.6%, respectively, as compared to the CK treatment. The Se treatments had a promoting effect on physiological indexes such as stem sheath length, lignin content in the stem sheath, and dry matter accumulation in different plant tissues, thereby increasing the total dry weight. The Se treatment had an inhibitory effect on chlorophyll b content and total chlorophyll content, whilst it increased the chlorophyll a content and chlorophyll a/b ratio, which in turn affected the photosynthesis of rice. Therefore, appropriate Se treatments (the application of 8 μmol·L−1 amino acid-chelated selenium, 4 μmol·L−1 sodium selenite, and 8 μmol·L−1 sodium selenite) could improve seedling growth and stem sheath hardness, which was related to the parameter changes, such as the dry weight, photosynthesis pigments, and peroxidase activity. These findings suggest that different Se fertilizers can positively regulate rice resistance to lodging and growth. This study can provide theoretical support for the application of selenium fertilizer.