Response to bradyrhizobium strain of peanut cultivars grown under iron stress

Abstract

An Fe efficient (Arachis hypogaea L. cv. 71–234) and an Fe inefficient (cv. Tainan 9) peanut cultivar were subjected to four inoculation treatments (NH₄NO₃ without inoculation, NC 92, TAL 1000 and a mixture of these two Bradyrhizobium sp. (Arachis) strains with THA 205) and grown under Fe stress conditions in complete nutrient solution including 0.2 mM NH₄NO₃ and 0.012 mM FeEDDHA at pH 8.6 maintained by addition of 5 mM NaHCO₃ and solid CaCO₃.

During the first four weeks, cv. 71–234 grew better than cv. Tainan 9 in all inoculation treatments but by eight weeks these differences had largely disappeared. By contrast, inoculation treatments had no effects on shoot and root dry matter at four weeks but large effects at eight weeks when plants inoculated with NC 92 alone or in a mixture had similar or more dry matter than those given NH₄NO₃ and double that of those with TAL 1000 alone. At four weeks, both cultivars had 250, 150, and 3 nodules per plant and acetylene reduction rates of 27, 17, <1 nmol/min/plant with NC 92, mixed inoculum, and TAL 1000 respectively: they also had 40, 150, and 1000 nodule initials per plant. At eight weeks both cultivars with TAL 1000 alone had N concentrations in their shoots well below those of all other treatments. Catechol type siderophore activity was present in solutions inoculated with NC 92 alone or in mixed inoculum but absent from those with TAL 1000 alone.

It is suggested that strains of Bradyrhizobium sp. differ profoundly in their ability to obtain iron from their environment for development of their symbiotic systems in peanut.

Key words:

• Fe efficiency
• Pe deficiency
• Nitrogen fixation
• Nodulation
• Arachis hypogaea L
• Siderophores