Abstract

Plants benefit extensively from endophytic and rhizospheric microbes. They promote plant growth and confer enhanced resistance to various pathogens. However, the interactions of these beneficial microbes are not always well understood. In this work, the interactions of two rhizospheric actinomycete strains DK56 (Streptomyces microflavus), ME2 (Micromonospora sp.) and endophytic bacterium strains XG32 (Pseudomonas fluorescens biovar. IV) and DP1 (Bacillus subtilis) were investigated via plate and broth cultivation. The strains were tested singly and in combinations for promoting the growth of tomato seedlings and biological control against pepper blight disease. The results indicated that there was nutrient competition between Micromonospora sp. ME2 and the two endophytic bacterium strains while S. microflavus DK56 competed with B. subtilis DP1 for nutrient when they were co-cultured in the plate. The growth of endophytic bacteria was inhibited by actinomycetes in broth. The plant growth promoting effect of endophytic bacteria was not influenced by the presence of other strains. Three strains S. microflavus DK56,Micromonospora sp. ME2 and P. fluorescens biovar. IV XG2 showed antagonistic activity againstPhytophthora capsici but they did not affect each other on the control of blight disease of pepper when co-inoculated with the sporangia suspension of P. capsici and the control effect on pepper blight disease ofMicromonospora sp. ME2 could be enhanced by B. subtilis DP1.

Key words: Actinomycetes, endophytic bacteria, interaction, growth-promotion, disease control.