The Effects of Different Exogenous Plant Hormones on the Lateral Root Development of <i>Malus hupehensis</i>

To investigate the impact of different exogenous plant hormones on the root phenotype, plant morphology, and endogenous hormone levels of Malus hupehensis seedlings, hydroponically cultivated seedlings were treated with different plant hormones, including IAA, IBA, GA, 6-BA, BR, and MeJA. The development of the plants was meticulously observed, and morphological indices (including the number of lateral roots, root length, root surface area, root volume, plant height, and stem diameter) as well as endogenous hormone levels (including ZR, IAA, ABA, GA1+3, JA, and BR) were measured. The results showed that auxins facilitated the lateral root development of M. hupehensis, whereas 6-BA impeded it. Compared with the control group, IAA and IBA enhanced the lateral root number, whereas 6-BA reduced it. BR was found to stimulate the development of plant height and stem diameter in M. hupehensis. Concurrently, the application of exogenous hormones also exerted influence on endogenous hormone levels. For instance, after treatment with 0.1mg L-1 BR, the levels of ZR, IAA, and GA1+3 in the lateral roots of M. hupehensis seedlings were markedly reduced, whereas after 0.1mg L-1 IAA treatment, the IAA and BR levels in the roots significantly increased, with concurrent notable decreases in ABA and GA1+3 levels. These findings provide a theoretical basis for the hormonal regulation of lateral root development in M. hupehensis.