Media Comparison for Enumeration of Actinobacteria and their Catabolic Diversity in the Crop Rhizosphere of Arid, Semi-Arid and Humid Regions (AER 3 and AER 6) of India

Abstract

Rhizosphere soils of sorghum, pearl millet, pigeon pea, finger millet and groundnut from sub-tropical arid and semi-arid regions (Karnataka, Andhra Pradesh and Rajasthan) and from humid pristine forest soils of Karnataka were used to enumerate actinobacterial populations and their catabolic diversity. The pH of the soils ranged from 5.7 to 9.1 and organic carbon content from 0.075 to 4.3%. Of five different cultural media used, Humic acid vitamin agar was found to be superior for enumeration of Actinobacteria. Forty one (41) Actinobacterial isolates were characterised for morphological and biochemical attributes and tentatively assigned to four genera - Streptomyces (26 no.), Nocardia (12), Micromonospora (1) and Saccharopolyspora (2). The catabolic diversity of Actinobacterial isolates (21 carbon compounds) showed that Shannon-Weaver diversity index (H) was high (3.54). Dendrogram of Actinobacterial isolates showed some degree of catabolic relatedness among arid and semi-arid zone isolates. All the isolates had 18% similarity. At 66% level of similarity there were 18 clusters and this diversity in carbon utilization was much more in the alkaline arid and semi-arid soils (2.81) than in the acidic humid soils (1.94). The species evenness in humid zone isolates (1.00) was slightly higher to that of arid and semi-arid zone (0.993) isolates. The results show that arid and semi-arid regions represent extremely rich reservoir for the isolation of a significant diversity of Actinobacteria and that Humic acid- Vitamin agar is best for recovering greater numbers and diversity.