Assessing the Biofortification of Wheat Plants by Combining a Plant Growth-Promoting Rhizobacterium (PGPR) and Polymeric Fe-Nanoparticles: Allies or Enemies?

Biofortification has been widely used to increase mineral nutrients in staple foods, such as wheat (<i>Triticum aestivum</i>). In this study, a new approach has been used by analyzing the effect of inoculation with a plant growth-promoting rhizobacterium (PGPR), namely, <i>Bacillus aryabhattai</i> RSO25 and the addition of 1% (<i>v</i>/<i>v</i>) of organometallic Fe-containing polymeric nanoparticles (FeNPs) alone and in combination. Previously, the minimal inhibitory concentration of FeNPs for the bacterium was determined in order not to inhibit bacterial growth. All treatments had minor effects on seed germination and plant survival. Considering the physiology of plants, several photosynthetic parameters were significantly improved in individual treatments with FeNPs or the bacterium, particularly the efficiency of the photosystem II and the electron transport rate, which is indicative of a better photosynthetic performance. However, at the end of the experiment, a significant effect on final plant growth was not observed in shoots or in roots. When using FeNPs alone, earlier spike outgrow was observed and the final number of spikes increased by 20%. Concerning biofortification, FeNPs increased the concentration of Fe in spikes by 35%. In fact, the total amount of Fe per plant base rose to 215% with regard to the control. Besides, several side effects, such as increased Ca and decreased Na and Zn in spikes, were observed. Furthermore, the treatment with only bacteria decreased Na and Fe accumulation in grains, indicating its inconvenience. On its side, the combined treatment led to intermediate Fe accumulation in spikes, since an antagonist effect between RSO25 and FeNPs was observed. For this reason, the combined treatment was discouraged. In conclusion, of the three treatments tested, FeNPs alone is recommended for achieving efficient Fe biofortification in wheat.