Rhizobial biofertilizers for ornamental plants

Abstract

Plant growth-promoting rhizobacteria (PGPR) are one of the most important groups of rhizospheric microorganisms, such as free-living bacteria, endophytes, and endosymbiotic bacteria. PGPRs colonize plant roots, conferring several benefits to the plants through different mechanisms. Despite its classical involvement in root nodule symbiosis with legumes, recent studies revealed the beneficial role of the genus Rhizobium as PGPR for several non-legume crops, supporting its inclusion in biofertilization schemes. However, studies based in the application of PGPRs as inoculants for ornamental crops are limited. Ornamental crops have a high economic importance for several regions, being Spain among the major producers of cut flowers. Due to their importance, we selected Dianthus caryophyllus (carnation) and a rhizobial strain for the evaluation of the PGPR effects in this plant. Selected strain was identified as Rhizobium sp. and presented PGPR mechanisms; phosphate solubilization, siderophores production, and IAA and precursors biosynthesis were positive. In vitro plant assays showed an increase in carnation development in early steps of plant development, when plants were inoculated respect to uninoculated plants. Moreover, effective root colonization was shown. Interestingly, an increase in root hairs redirections was observed in inoculated plants. To the best of our knowledge, this is the first study reporting the effects of Rhizobium in D. caryophyllus, showing effective root colonization and an improvement in early stages of plant development.