The plant growth promoting bacteria Gluconacetobacter diazotrophicus and Azospirillum brasilense contribute to the iron nutrition of strawberry plants through siderophores production

Gluconacetobacter diazotrophicus PAL5 and Azospirillum brasilense REC3 are plant growth promoting bacteria. They are able to produce hydroxamate and catechol type siderophores, respectively, when iron is not available, chelating this metal to facilitate its absorption. Iron is required by plants and is involved in physiological processes as part of many important compounds. The aim of this work was to evaluate the two siderophores producing bacteria in their contribution to iron nutrition for strawberry plants through the growth index, leaf and root area, greenness index, total soluble phenolic compounds and total iron content. Strawberry plants were grown hydroponically with a 16-h photoperiod in Hoagland nutrient solution, modified in iron sources, and inoculated with each bacterium. At day 60, the highest values of growth index, root area, greenness index, and iron content, were obtained for treatments with reduced iron, and the lowest values in treatments without iron addition. Values in treatments with oxidized iron and inoculated with bacteria were similar to those obtained with reduced iron and uninoculated plants. At day 30, phenolic compounds were higher in treatments without iron addition and uninoculated, while they decreased when plants were inoculated. For treatments with reduced iron, phenolic compounds content was low and increased when plants were inoculated. In conclusion, the siderophores produced by G. diazotrophicus PAL5 and A. brasilense REC3 can contribute to the iron nutrition of hydroponically grown strawberry plants. The participation of the hydroxamates was better than that of the catechols in the provision of iron to the plants.