Casuarina cunninghamiana tissue extracts stimulate the growth of Frankia and differentially alter the growth of other soil microorganisms

Aqueous extracts of host plant Casuarina cunninghamiana tissue altered the in vitro growth of its diazotrophic microsymbiont Frankia and a selection of other soil microorganisms. The growth of actinomycetous Frankia strains, 55005, AvcI1, CesI5, CjI82 001, and Cj was stimulated by aqueous extracts of C. cunninghamiana tissue. Green cladodes ( photosynthetic branches), unsuberized roots, and suberized roots were more stimulatory than dry cladodes and seed tissue. Aqueous extracts of green cladodes of C. cunninghamiana most stimulated the growth of Casuarina-derived Frankia strains CjI82 001 and 55005. The growth of isolates of soil bacteria Bradyrhizobium japonicum, Arthrobacter globiformis, and Bacillus subtillis and of the soil fungi Penicillium oxalicum and Arthroderma cookiellum was either inhibited or not affected by cladode extracts. Cladode extracts stimulated the growth of the actinomycete Streptomyces albus and the fungus Rhizopus homothallicus. The magnitude ( as great as 100%) of the increase in growth caused by tissue extracts for the Casuarina-derived Frankia strains relative to other soil microbes suggests a host-specific enhancement of the microsymbiont.