Growing gladiolus corms in soil-less culture fertilized by soluble nutrients raised the question of how both
Trichoderma harzianum and Aneurinobacillus migulanus enhance plant growth and provide protection against
infection by Fusarium oxysporum f. sp. gladioli. Changes in the concentrations of the plant growth regulators
(PGRs) gibberellic acid (GA3), indole acetic acid (IAA) and abscisic acid (ABA) were determined in gladiolus
corms following treatment with T. harzianum, A. migulanus and F. oxysporum f.sp. gladioli. The presence of these
PGRs in corms was confirmed using liquid chromatography-mass spectrometry (LC-MS/MS) and the compounds
quantified using high performance liquid chromatography (HPLC). Concentrations of both GA3 and IAA increased
linearly in all corms over the 10 days after treatments; lowest concentrations of both PGRs were consistently found
in corms inoculated with F. oxysporum f. sp. gladioli. In contrast, highest concentrations of both GA3 and IAA
occurred in corms treated with T. harzianum alone. Highest concentrations of ABA, however, were found in corms
inoculated with F. oxysporum f. sp. gladioli, regardless of the presence of T. harzianum or A. migulanus. Treatments
with T. harzianum or A. migulanus in the absence of F. oxysporum f.sp. gladioli maintained ABA concentrations at
the same levels as control corms. These results indicate that promotion of Gladiolus growth by T. harzianum or A.
migulanus may be partly mediated through stimulation of the production of GA3 and IAA in corm tissues. Increases
in these PGRs may also be a mediator in the biological control activity shown by T. harzianum or A. migulanus.