The objective of this work was to investigate the ability of
the plant growth-promoting rhizobacterium Pseudomonas
aureofaciens 63-28 to induce plant defense systems,
including defense-related enzyme levels and expression of
defense-related isoenzymes, and isoflavone production,
leading to improved resistance to the phytopathogen
Rhizoctonia solani AG-4 in soybean seedlings. Seven-dayold
soybean seedlings were inoculated with P. aureofaciens
63-28, R. solani AG-4, or P. aureofaciens 63-28 plus R.
solani AG-4 (P+R), or not inoculated (control). After 7
days of incubation, roots treated with R. solani AG-4 had
obvious damping-off symptoms, but P+R-treated soybean
plants had less disease development, indicating suppression
of R. solani AG-4 in soybean seedlings. Superoxide
dismutase (SOD) and catalase (CAT) activities of R. solani
AG-4-treated roots increased by 24.6% and 54.0%,
respectively, compared with control roots. Ascorbate
peroxidase (APX) and phenylalanine ammonia lyase (PAL)
activities of R. solani AG-4-treated roots were increased by
75.1% and 23.6%, respectively. Polyphenol oxidase (PPO)
activity in soybean roots challenged with P. aureofaciens
63-28 and P+R increased by 25.0% and 11.6%, respectively.
Mn-SOD (S1 band on gel) and Fe-SOD (S2) were strongly
induced in P+R-treated roots, whereas one CAT (C1) and
one APX (A3) were strongly induced in R. solani AG-4-
treated roots. The total isoflavone concentration in P+Rtreated
shoots was 27.2% greater than the control treatment.
The isoflavone yield of R. solani AG-4-treated shoots was
60.9% less than the control.

Keywords: Defense enzymes, isoflavones, Pseudomonas aureofaciens, Rhizoctonia solani, Soybean