Effects of Chemical Seed Treatments of Soybean Bacteria Pustule, on Rhizobium Symbiosis and Yield of Soybean

Abstract

Seven chemical compounds, including antibiotics and fungicides, namely Aureomycin, Dumocycline, Agrimycin-100, Terramycin, Tersan 75, Thane M-45 and Cupravit, used in seed treatment of soybean to control bacterial pustule, were examined for their effects on Rhizobium nodule bacteria both under laboratory and field trials, at Kasetsart University Bangkhen Campus and Suwan Farm respectively. In the laboratory, chemicals applied at 250 ppm inhibited the growth of 5 strains of Rhizobium japonicum, namely USDA 8-0, USDA 15-7, USDA 110, USDA 122 and TH7. An exception was found with Agrimycin-100 which inhibited the growth of Rhizobium strain TH7, only above 1,500 ppm. In a field test, the same 7 chemicals were used as a seed treatment of soybean varieties SJ2, SJ4 and SJ5, both with and without inoculation with Rhizobium. The results revealed no significant differences in fresh nodule weight and 100-seed weight. Seeds treated with fungicides had significantly higher number of plants per unit area and seed yield compared with seeds treated with antibiotics or untreated seeds. Among soybean varieties, only inoculated seeds of JS4 had higher yield than without Rhizobium inoculation.