Growth and acetylene reducing activity of azospirilla as affected by interaction with soil streptomyces, penicillia and fusaria

Abstract

A total of 68 actinomycete and 63 fungal isolates obtained from various soils were tested for their ability to antagonize different strains of Azospirillum in sterile soil. It was found that between 78 and 87% of the streptomycete and between 75 and 83% of the fungal isolates respectively did not inhibit azospirilla. Numbers of azospirilla in soil were seriously reduced when they interacted with some of the streptomycete and fungal isolates. In soil treated with both azospirilla and either streptomycetes or fungi, the nitrogenase activity ranged from ca 2–210 nmol C 2H 4g −1h −1. In general, the acetylene reducing activity (ARA) in soils treated with fungi was reduced more seriously than those treated with streptomycetes; the mean ARA reported in the presence of fungi was 23 nmol C 2H 4g −1 h −1 against 48 in the presence of streptomycetes. The reduction in both azospirilla number and ARA in soil may have reflected the increasing population of antagonists. Highly-significant negative correlations between the diameter of inhibition zones produced by the active Streptomyces and fungal isolates using the agar-disc method were found with both numbers and ARA of most Azospirillum strains in soil.