Effects of the auxin synthesis inhibitor yucasin and the auxin transport inhibitor 1-N-naphthylphthalamic acid (NPA) on Pinus massoniana root development induced by Suillus bovinus volatile organic compounds (VOCs). Effects of adding different concentrations of the indole-3-acetic acid (IAA) synthesis inhibitor yucasin to medium inoculated with S. bovinus, or containing α-humulene or β-cedrene on a the number of P. massoniana root branches and b root length. The absence of some data for seedlings subjected to 50 M or 100 M yucasin is because P. massoniana wilted under these treatments. Effects of adding different concentrations of the IAA transport inhibitor NPA to medium inoculated with S. bovinus or containing α-humulene or β-cedrene on c the number of P. massoniana root branches and d root length. n = 15. Different letters above bars indicate significant differences between treatments (P < 0.05).