Foliar application uniconazole enhanced lodging resistance of high-quality indica rice (Oryza sativa L. ) by altering anatomical traits, cell structure and endogenous hormones

Lodging is an important limiting factor for increasing yield and quality in high-quality indica rice production. The objectives of this study were to explore the mechanism of lodging resistance in high-quality indica rice as affected by anatomical and cellular structure, especially its related endogenous hormone changes in culm tissue and response to foliar application uniconazole. Field experiments were conducted in Shanggao County, Jiangxi Province, China, by using two indica rice varieties Meixiangzhan2 (MXZ2) and Taiyou871 (TY871) with two foliar application uniconazole rates (0 mg L−1, U0; 80 mg L−1, U1) in 2019 and 2020. The results showed that the foliar application uniconazole affected the grain yield quite low, but decreased lodging index (LI) value with significant difference in both two varieties and years. Compared with U0 treatments, U1 treatments rapidly shortened length of basal internodes, especially for IN4, but affected length of upper internodes slightly, which resulted in reduction of length from breaking basal internode to top (SL) and bending moment by the whole plant (WP) value. The shorter cell length and denser cell arrangement under U1 treatments, which were induced by lower endogenous indole acetic acid (IAA) and gibberellin A3 (GA3) content in culm tissue, declined the length of IN4 internodes, plant height and center of gravity height. The higher breaking strength (M) was resulted from larger section- modulus (SM) of TY871 and higher bending stress (BS) of MXZ2, respectively. The elevated endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and zeatin (Z) content increased cell division in culm tissue and thus, raised the culm wall thickness, culm and leaf sheath cross sectional area and SM in basal internodes. Compared with U0 treatments, U1 treatments increased cell wall components including cellulose and lignin, starch, as well as higher BS in both TY871 and MXZ2. These results suggested that reduction of plant height and center gravity height were induced by shorter cell length and denser cell arrangement, which resulted from lower endogenous IAA and GA3 in culm tissue. The foliar application uniconazole could enlarged culm wall thickness and SM by elevate endogenous ACC and Z content, and increase stem strength by higher carbohydrates including cellulose, lignin and starch and thereby, enhanced lodging resistance of high-quality indica rice.