Ethephon mediates root morphology traits for shaping steep root architecture to enhance root anchorage in maize

Ethephon (ETH) is widely applied to shape plant type for enhancing plant lodging resistance in maize high-yield and efficient production, however, there is limited information on how ethephon regulates root traits to mediate root anchorage strength for enhancing the lodging resistance. To clarify this, a two-year field experiment (2022 and 2023 summer maize growing seasons) was conducted to evaluate the regulatory effect of ETH application on the root development, morphological traits and anchorage strength in three maize varieties. ETH application advanced nodal root initiation, accelerated the growth rate of nodal root development, shortened the developmental duration of root whorl, and induced the formation of an additional nodal root whorl without significantly affecting nodal root number per whorl. Meanwhile, ETH application significantly increased root length and lateral root number, but reduced root diameter and root volume. Furthermore, ETH application increased root angle, top root angle and bottom root angle, while decreasing maximum and median width of root system, which facilitated the development of a steeper and more compact root system architecture. In addition, ETH application strengthened root anchorage by improving vertical root pulling resistance (VRPR), failure angle, anchorage strength and safety factor by 20.6, 18, 20.7, and 68.8%, respectively. Meanwhile, an increased root-to-shoot ratio of 14.7%, along with reductions in the ratios of plant height to VRPR and shoot fresh weight to VRPR of 21.5 and 26.8%, respectively, collectively indicated more efficient root development and improved shoot-root interaction in ETH-treated plants. Moreover, ETH effectively reduced the lodging rates by 73.9%, while increased the number of harvest ears, improved the grain yield and harvest index. Overall, ETH could mediate root morphology traits to shape steep root architecture and improve shoot–root interaction for enhancing the lodging resistance in maize.