Characterization and plant growth promoting potential of microbial groups associated with a Coffea sp. collection

The genus Coffea spp. is the most important of the Rubiaceae family and both Coffea arabica L. and Coffea canephora P. constitute the most economically important species. This research aimed to characterize morphologically, physiologically and biochemically diazotrophic rhizobacteria associated with coffee plants from a living collection, and to study their plant growth promoting potential. Semi-solid nitrogen-free media NFb and JNFb were used to isolate the bacteria. Ten isolates were selected for micro-morphological, physiological-biochemical and plant growth potential characterization. The solubilization of calcium phosphate, the synthesis of indole compounds and the production of siderophores were analyzed. The results showed that high population levels of bacteria, fungi and actinomycetes are present in the rhizosphere of the coffee collection. 95 native isolates were selected, and 8 were classified as Azospirillum and Herbaspirillum. Phosphate solubilizing activity was detected in the ten isolates, highlighting the C8 isolate. Synthesis of indole compounds was also detected by the ten isolates, although in amounts significantly lower than the controls. Only isolates C2, C9 and C10 produced siderophores. The multivariate cluster analysis resulted in the formation of three groups, the C8 grouped with the positive control in one of them. The beneficial potential of this isolate makes it a source of interest to develop a biostimulant product that could be applied as a sustainable alternative for the cultivation of Coffea sp.