Diversity of Actinomycetes in Nitrogen Fixing Root Nodules of Casuarinaequisetifolia and its Impact on Plant Growth

Abstract

Casuarinaequisetifolia (Kasa) is an actinorhizal plant which is used for rehabilitation of poor and disturbed soil throughout the world. Actinorhizal plants which were colonized by Frankia sp. enhance the soil fertility due to frankial colonization in root nodules. However, few studies were reported on non-frankial colonization and its impact on plant growth and soil fertility. Thus this study was carried out to investigate the unrevealed information on actinomycete consortia residing the nitrogen fixing root nodules of C. equisetifolia. The actinomycete were successfully isolated from surface sterilized root nodules by using double layered agar plate technique and also isolates were tested on reinfectivity on Casuarina seedlings. Three different actinomycetes were able to identify as Frankia sp., Micromonospora sp., and novel symbiont as Streptomyces sp. from nitrogen fixing root nodules of Casuarina plants. Further, co-existence of all three isolates were observed in nitrogen free and nitrogen enriched Yeast Mannitol Agar medium (YMA). Frankia sp. promoted the shoot and root growth by 87% and 55% respectively with nodulation of C. equisetifolia and whereas Micromonospora sp. promoted the root and shoot growth by 28% without nodulation. In contrast Streptomyces sp. was able to trigger the lateral root formation of C. equisetifolia which indicate the ability of the microorganism to alter host development system. This study provides novel data on root inhabiting Streptomyces sp. which could play a vital role in enhancing plant growth, exchanging complex signals between plant and microorganisms. These results suggest that the root inhabiting microbial consortium of C. equsetifolia would significantly contribute to the development of plant growth.