Bradyrhizobium japonicum Preincubated with Methyl Jasmonate Increases Soybean Nodulation and Nitrogen Fixation

Jasmonates (jasmonic acid and methyl jasmonate) are naturally occurring plant hormones biosynthesized in response to wounding and biotic and abiotic stresses. Besides their role in planta, they can act as signaling molecules in soybean ( Glycine max )– Bradyrhizobium symbioses by inducing the transcription of nodulation genes. Previous studies have shown that inoculation of soybean with Bradyrhizobium japonicum preinduced with genistein (Ge) or methyl jasmonate (MeJA) promoted soybean nodulation and N fixation under controlled environment conditions. We conducted two separate field experiments in the year 2002 to study the effect of preinducing B. japonicum strains with methyl jasmonate (MeJA), alone or in combination with Ge, on nodulation and N fixation under field conditions. Two B. japonicum strains (532C and USDA3) and four inducer treatments (control, MeJA, Ge, and MeJA plus Ge) were formulated. Genistein and MeJA increased nodule number, nodule dry weight per plant, and seasonal N fixation, as compared with the control treatment, inoculated with uninduced B. japonicum . These results demonstrate that methyl jasmonate alone or in combination with Ge can be used to promote soybean nodulation and N fixation under short‐season field conditions.