Trichoderma harzianum strain T-22 induces changes in phytohormone levels in cherry rootstocks (Prunus cerasus x P-canescens)

The aim of this research was to explain the direct plant growth-promoting activity of Trichoderma harzianum strain T-22 (T22), hypothesizing the involvement of different classes of plant growth regulators. Seven days after the transfer to root-inducing medium, in vitro-cultured shoots of GiSeLa6(R) (Prunus cerasus x P. canescens) were inoculated with T22. Root and shoot growth were significantly affected by T22 (+76 and +61%, respectively). Ten days after inoculation, the levels of indole-3-acetic acid (IAA), trans-zeatin riboside (t-ZR), dihydrozeatin riboside (DHZR), gibberellic acid (GA3) and abscisic acid (ABA) were analyzed by high performance liquid chromatography coupled with mass spectrometry. The results showed that after T22-inoculation, IAA and GA3 significantly increased in both leaves (+49 and +71%, respectively) and roots (+40 and +143%, respectively) whereas t-ZR decreased (-51% in leaves and -37% in roots). Changes in DHZR were observed in T22-inoculated roots (-32%) but not in leaves, whereas the levels of ABA did not differ between the two treatments. The extraction method allowed the simultaneous extraction of phytohormones. There is evidence that the change in phytohormone levels is one of the direct mechanism by which T22 promotes rooting and shoot growth, with notable advantages for rootstock production during nursery processes.