Helper rhizoactinomycetes on Discaria trinervis-Frankia symbiosis.

SOLANS M; CHAIA E; VOBIS G; WALL LG

Umea, Suecia

Simposio; 14 th Meeting on Frankia and actinorhizal plants; 2006

The aim of the present study was to examine the possible effect of saprophytic and rhizospheric actinomycetes (rhizoactinomycetes) as “helper bacteria” in the D. trinervis – Frankia symbiosis. It was hypothesized that due to the capabilities of Streptomyces (MM40), Micromonospora (MM18) and Actinoplanes (ME3) to degrade cellulose, hemicellulose, pectin and lignin, the co-inoculations of these strains and Frankia BCU110501, would improve the actinorhizal nodulation in D. trinervis. D. trinervis seedlings were single, double or triple inoculated with Frankia and/or with each rhizoactinomycete strain. Double inoculations were also performed either simultaneously or at different times. In general, the co-inoculations with Frankia and saprophytic strains showed a positive effect in the actinorhizal symbiosis. The plants that were first inoculated with Frankia and then co-inoculated with one of the saprophytic strains, produced a higher number of nodules per-plant or nodule dry mass. Nodule development time course during  the first weeks post-inoculation was faster for single inoculated plants with Frankia, but the final nodule number per plant was slightly higher in co-inoculated plants with Frankia + Actinoplanes and Frankia + Micromonospora.  These results suggest that saprophytic strains of actinomycetes have a helper effect in the actinorhizal symbiosis, mainly enhancing the nodulation and consequently the promotion of D. trinervis growth.