The effect of fungicides on type of Rhizobia inoculted for optimum soybean production under field condition were investigated. In the present study, statistically significant interaction between seed applied fungicide and Rhizobial inoculant were detected for nodulation and yield of soybean. Application of Rhizobial inoculants alone were provided the highest nodulation and shoot dry weight performance as well as seed yield of soybean at both sites. SB-12 inoculant had significantly (P < 0.05) shown to be more effective than SB-14 inoculant in increasing nodulation and thus produced higher plant growth and seed yield. Rhizobial survival on the seeds was affected severely by both fungicides, resulting in decreased nodulation, plant growth and seed yield for both inoculants in both locations. However, Ridomil fungicide gave the lowest nodulation and seed yield when applied with either SB-12 or SB-14 Rhizobial strains. The strains differed in their sensitivity to mancozeb fungicide that with strain SB-12 showed a slight effect or no effect on survival of rhizobium, nodulation and yield of soybean. Seed dressing of mancozeb and Ridomil resulted in reduction of seed yield by 882.8 and 1154.7 kg ha-1, respectively with SB-12 strain. The present results indicate that inoculated Rhizobium inoculants differ in their capacity to develop resistance to the two dressed fungicides. Seed treatment with mancozeb in combination with SB-12 strain slightly affected the survival of the inoculated strain. Consequently, mancozeb fungicide was compatible with survival of the inoculated SB-12 Rhizobia. The results also indicate that fungicide seed dressing used to improve the early plant emergence on soybean plant were damaging to Rhizobium strains. However, the suppressive effect of seed-applied fungicides on Rhizobium strains survival and nodulation depend on specific strain and fungicide. Soybean seeds inoculated with SB-12 would not need management with fungicides or lower concentration of mancozeb that could be compatible with SB-12 to suppress soil-borne pathogens for both Assosa and Begi sites.

Keywords: Rhizobium strain, Fungicides, Nodulation, Soybean, Yield