Use of Neomycin for Preferential Selection against Rhizobium trifolii in Symbiosis with White Clover (Trifolium repens)

Abstract

Symbiotic parameters were tested on neomycin-containing media with antibiotic-sensitive and -resistant Rhizobium trifolii inoculants. Neomycin and kanamycin have similar inhibitory effects on R. trifolii, either antibiotic inhibiting growth at concentrations of 50 mg/!. Transposon Tn5 conferred kanlllTlycin and neomycin resistance to R. trifolii allowing growth on media supplemented with antibiotic *p to concentrations of 400 mg/!. Differential inhibition of nitrate-grown white clover (Trifolium repens) plants in an axenic culture system (Petri plates) was observed in terms of dry weight accumulation and ~isual characteristics. Kanamycin at 50 mgll and neomycin at 200 mgll had similar inhibitory effects on plant growth. Symbiotic development by sensitive R. trifolii cells was severely inhibited by neomycin at concentrations between 50 and 100 mg/l. Plants nodulated by resistant R. trifolii strains maintained co~trol levels of nitrogen ilxation with neomycin concentrations up to 150 mg/!. Thus neomycin is propbsed to be useful as a selective agent against revertants which have lost transposon Tn5 in planta as well as ex planta.