XVI International Botanical Congess

Actinorhizal plants form root nodules with the symbiotic, diazotrophic actinomycete Frankia. Actinorhizal Casuarina cunninghamiana trees are planted as windbreaks in Jamaica and are naturalized in coastal areas. Soil sampled around C. cunninghamiana was bioassayed to estimate the number of infective units Frankia g-1 soil, using native Myrica cerifera and exotic C. cunninghamiana as Frankia traps. Casuarina-infective Frankia was localized within 20 m of its host, whereas Myrica-infective Frankia occurred independently of host presence throughout this site. Microsymbiont characterization using PCR and RFLP indicated that Casuarina and Myrica were nodulated by different Frankia genotypes. Homogenates of C. cunninghamiana cladodes increased the number of infective units of Frankia strain CjI82 incubated in an artificial soil. Thus, C. cunninghamiana may be able to favor its specific introduced microsymbiont in soil.