Abstract: Elucidating the effects of waterlogging during internode elongation stage on stem growth and lodging resistance of wheat can provide comprehensive understanding of the mechanisms underlying waterlogging damage and lodging, which will benefit the stress-resistant and stable wheat production. We examined the effects of waterlogging stress on internode morphological and mechanical indicators at the flowering and milking stages of Yangmai 25. Waterlogging treatments were applied from the initiation of 1 cm elongation in the basal 1^st (B1), 2^nd (B2), 3^rd (B3), 4^th (B4), and 5^th (B5) internodes, which lasted for 7 days each. The non-waterlogging treatment (CK) was used as the control. The results showed that waterlogging treatments significantly inhibited the elongation of undetermined internodes (internode not fully elongated to final length), and thus reduced plant height and center cgravity height at the milking stage. The B2 treatment resulted in the greatest decreases in plant height and center cgravity height, reaching 9.5% and 8.4%, respectively. Waterlogging significantly reduced the outer diameter and wall thickness of the 2^nd, 3^rd, 4^th, and 5^th internodes at both the flowering and milking stages, and decreased the filling degree of each internode at the flowering stage. Furthermore, waterlogging treatments significantly reduced the bending moment of each internode at the flowering and milking stages, and decreased the breaking resistance of internodes across stages. Specifically, B1 and B2 treatments significantly reduced the breaking resistance of all internodes, while B4 and B5 treatments mainly reduced the breaking resistance of upper internodes. The breaking resistance of the second internode (the main internode responsible for lodging) under different treatments followed the order: B2<B1<B3<B4<B5<CK. Treatments B1, B2, and B3 significantly increased the lodging index of the 1^st, 2^nd, and 3^rd internodes, whereas no significant effects were found under B4 and B5 treatments. Linear correlation analysis of the morphology and lodging resistance of the basal 2^nd internode indicated that improving the outer diameter and wall thickness of internodes could significantly enhance breaking resistance and reduce the lodging index. In summary, waterlogging stress during the internode elongation stage of wheat inhibited internode elongation, thickening, and wall development, thereby deteriorating internode structure, reducing breaking resistance, and increasing lodging risk. The most pronounced effects were observed during the elongation of the basal first and second internodes.

Key words: wheat, internode, waterlogging stress, growth, lodging resistance