Growth stimulation of the actinorhizal plant Discaria trinervis by symbiotic and saprophytic strains of actinomycetes

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

Melbourne, Australia

Simposio; 13th International Symposium on the Biology of Actinomycetes; 2003

The symbiotic relationship between Discaria trinervis (Hook. et Arn.) Reiche and Frankia strain BCU 110505 was investigated previously (Chaia 1998, Wall et al. 2002). To study the possible role of saprophytic actinomycetes as "plant growth promoting rhizobacteria", altogether 122 strains were isolated from rhizosphere. Three strains with enzymatic activity to degradate starch, pectin, hemicellulose and cellulose, were selected for inoculation essays: Streptomyces MM40, Actinoplanes ME3, and Micromonospora MM18. Inoculated seedlings were grown in glas tubes on vermiculate-sand for 12 weeks, fertilized with Evans nutrient solution with low concentration of nitrogen. Subsequently, the development of stems, leaves and roots of each individual was analysed and mutually compared. Non-inoculated control plants developed shoots of about 3 cm height and roots with16 cm length on the average. Plants inoculated only with saprophytic strains, reach the same height of stems, but present a significant better development of root systems. All Frankia-inoculated plants produce root nodules, with an increasing number from 15 in simply inoculated specimen up to 31 nodules in plants, co-inoculated with Actinoplanes. All co-inoculated plants show very well developed shoots, reaching 17 cm length. It was possible to demonstrate, that not only Frankia as dinitrogen fixing symbiote, but also saprophytic strains have positive effects on the growth of D. trinervis. Combined inoculations intensify the stimulation. Strains from the rhizosphere can promote the development of the root system, including the formation of nodules. Frankia promotes first of all the growth of stems and leaves, rather than the development of the root.