Aims: The purpose of this study was to analyse the effects of siderophore-producing bacteria and bacterial siderophore on the iron nutrition of apple rootstocks under iron-deficient conditions.
Methods and results: We isolated three Pseudomonas strains, SP1, SP2 and SP3 from the rhizosphere of the Fe-efficient apple rootstocks using the chrome azurol S agar plate assay. We found that all three strains had the ability to secrete indole acetic acid-like compounds and siderophores, especially SP3. When Fe-inefficient rootstocks treated with SP3 were grown in alkaline soil, an increase in the biomass, root development, and Fe concentration was observed in the plants. In addition, SP3 secreted pyoverdine, a siderophore that can chelate Fe3+ to enhance the bioavailability of Fe for plants. We purified the pyoverdine from the SP3 culture supernatant. Hydroponic experiments were conducted with a Fe-deficient solution supplemented with pyoverdine, resulting in a reduction in the chlorosis caused by Fe deficiency and marked improvement in Fe uptake.
Conclusions: Under iron-deficient conditions, Pseudomonas sp. strain SP3 can effectively promote apple rootstock growth and improve plant iron nutrition by secreting siderophores that enhance Fe availability.
Significance and impact of the study: This study showed that plant growth-promoting rhizobacteria from Fe-efficient plants have the potential to improve iron nutrition in Fe-inefficient plants, and Fe-siderophore chelates can be used as an effective source of iron for apple plants. Based on these findings, it may be possible to develop biological agents such as siderophore-producing bacteria for sustainable agricultural and horticultural production.
Keywords: pseudomonas; PGPR; apple rootstock; iron; siderophore.
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