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Actinorhizal plants can contribute to the rehabilitation of poor and disturbed soils by stabilizingthe
soil and building up its nitrogen content. In addition, they can withstand under variousenvironmental
stresses such as high salinity, heavy metal, etc., Casuarina equisetifolia is an actinorhizal plant which
is important in agroforestry, land reclamation and natural ecosystems. The aim of this study was to
explore microbial diversity in nitrogen fixing nodules of C. equisetifolia and to assess its impact on
plant growth and soil quality.
Double layered agar plate technique was adopted to isolate microorganisms from surface-sterilized
root nodules. Isolated microorganisms were identified based on distinctive morphological
characteristics of colonies and mycelia which were observed under light microscope. Ability of
isolates to grow with cadmium up to 10 mg/mL was also tested.Two weeks old seedlings of C. _
• equisetifolia which were grown in V* strength Hoagland’s nutrient solution (pH 6.8)7were inoculated
with different isolates to examine infectivitv. nodulation and their effect on shoot and root growth of
C. equisetifolia. The root, shoot length, lateral root formation, nodulation were recorded. The plant
assay was conducted in triplicate in a completely randomized block design.
Three actimomycetes species .Frankiasp., Micromonospora sp. and Streptomyces sp.were identified
from nitrogen fixing root nodules. Further, synergistic growth of all three isolates in liquid media with
and without any nitrogen supplement was observed. While Frankia sp. promoted the shoot and root
growth by 87% arid 55% respectively with nodulation of C. equisetifolia, about 28% increase in shoot
and root growth of C. equisetifolia by Micromonospora sp. without nodulation was observed. In
contrast, lateral root formation ofC.equisetifolia found to be triggered by Streptomyces sp. indicating
its potential to modulate host developmental pathways. This study provides novel data on isolation of
root inhabiting Streptomyces sp. which could probably play a vital role in exchanging complex signals
between plants and the microorganisms and alleviating cadmium toxicity to the plant by depleting
caecum availability in soil. In conclusion, the plant probiotic role of nodule inhabiting
actinomycetes of C. equisetifolia v/ovid significantly contribute to the plant growth and soil quality.
