Sampling to determine nodule occupancy of soybean (Glycine max (L) Merr.) by Bradyrhizobium japonicum strains

Abstract

The confidence interval of the percentage of soybean (Glycine max. (L.) Merr.) nodule occupancy by two strains of Bradyrhizobium japonicum was studied using samples of nodules per plant varying by multiples of 8 (8-56). These samples were recovered from all of the nodules of four sets of 21-24 plants grown in soil colonized only by these strains and typed using strain-specific sera. Approximate confidence intervals (ACI) were estimated (from the ANOVA model) using the formula, length of ACI = 4 [(0.040/P) + (0.278/PN)]1/2, where P is the number of sampled plants and N is the number of nodules characterised for each plant. The estimated ACI decreased when the number of plants sampled increased and decreased to a lesser extent when the number of nodules typed per plant increased. It was possible to define a plant and nodule sampling strategy to minimize the labor and time required to get acceptable ACI values. Under our experimental conditions, when 192 nodules were typed, combinations of 24 plants × 8 nodules per plant and 32 plants × 6 nodules per plant were the most satisfactory, corresponding to calculated ACI of 22.3 and 20.8%, respectively.Key words: Bradyrhizobium japonicum, competition, method, nodule occupancy, soybean.