Helper rhizoactinomycetes on Discaria trinervis-Frankia symbiosis

SOLANS, M; CHAIA, E; VOBIS, G; WALL, LG.

Umea, Suecia

Congreso; 14th International Meeting on Frankia and Actinorhizal plants; 2006

Umea University

The aim of the present study was to examine the possible effect of saprophytic and rhizospheric isolated actinomycetes (rhizoactinomycetes) as ?helper bacteria? in the Discaria trinervis ? Frankia symbiosis. It was hypothesized that due to the capabilities of Streptomyces (MM40), Micromonospora (MM18) and Actinoplanes (ME3) to degrade starch, cellulose, hemicellulose, pectin and lignin, the co-inoculations of these strains with Frankia BCU110501, would improve the actinorhizal nodulation in D. trinervis. Seedlings were inoculated with Frankia and in combination with each rhizoactinomycete strain. Double inoculations were performed either simultaneously or at different times. In both cases, the co-inoculations with Frankia and saprophytic strains showed a positive effect on the actinorhizal symbiosis. In simultaneous inoculations, the time course of nodule development during  the first weeks of 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. The plants that were first inoculated with Frankia and then co-inoculated with the saprophytic strains, produced a higher number of nodules per plant or dry mass of nodules. These results suggest that saprophytic strains of actinomycetes may have a helper effect in the actinorhizal symbiosis, enhancing the nodulation.