PGPR’s mix treatment to Moringa improved plant growth and iron content in foliage as substantiated by biochemical and molecular methods

Induced Systemic Resistance (ISR) and Fe Deficiency Responses in Dicot Plants

“…In contrast to the negative effect of some soil-borne pathogens on Fe acquisition, there are several recent reviews showing an important role of beneficial rhizosphere microbes on the Fe nutrition of plants ( Jin et al, 2014 ; Mimmo et al, 2014 ; Pii et al, 2015 ; İpek and Esitken, 2017 ). These microbes can directly improve Fe nutrition through the release of H + and/or Fe- solubilizing compounds to soils, like siderophores and organic acids, or by inducing changes in root physiology and architecture, which can improve the acquisition of Fe and also of other nutrients ( Orozco-Mosqueda et al, 2013 ; Jin et al, 2014 ; Mimmo et al, 2014 ; Zhao et al, 2014 ; Contreras-Cornejo et al, 2015 ; Pii et al, 2015 , 2016b ; Garnica-Vergara et al, 2016 ; Scagliola et al, 2016 ; Verbon and Liberman, 2016 ; Zhou et al, 2016a , b ; Martínez-Medina et al, 2017 ; Sonbarse et al, 2017 ; Sharifi and Ryu, 2018 ; Stringlis et al, 2018a ). In this way, it has been demonstrated that ISR-eliciting microbes can induce Fe deficiency responses in their host roots, such as enhanced ferric reductase activity, acidification of the rhizosphere, release of phenolics and flavins, and development of root hairs; and the expression of the genes associated with these responses, such as FIT , bHLH38 , bHLH39 , MYB72 , MYB10 , FRO2 , IRT1 , AHA , F6′H1 , BGLU42 , ABCG37 , and others ( Figure 1 , 2 and Table 1 ; Ribaudo et al, 2006 ; Zhang et al, 2009 ; Zamioudis et al, 2014 , 2015 ; Zhao et al, 2014 ; Pii et al, 2016b ; Scagliola et al, 2016 ; Verbon and Liberman, 2016 ; Zhou et al, 2016a , b , 2018 ; Martínez-Medina et al, 2017 ; Verbon et al, 2017 ; see also Section “Fe deficiency responses in dicot plants” and Section “Rhizosphere microbial species that induce Fe deficiency responses and improve Fe acquisition”).…”

“…More research is also needed to know the best ways for their application, by analyzing and comparing, both biologically and economically, the different possibilities, like direct application to soil, root immersion of plantlets before transplanting them (in the case of crop trees), application to seeds, and application into the irrigation systems (probably as spores). In the same way, it is necessary to study whether it is better to apply individual microbial species or consortia of different microbial species ( Alizadeh et al, 2013 ; Sonbarse et al, 2017 ). In this latter case, and since ET can play a dual role in both ISR and Fe deficiency responses, it would be interesting to analyze the interactions between plant species and microbial species possesing the ACC deaminase enzyme and those that do not.…”

“…Several studies demonstrated that the application of some beneficial microbes to soils can improve the Fe nutrition of plants ( de Santiago et al, 2009 , 2013 ; Zhang et al, 2009 ; Freitas et al, 2015 ; Li et al, 2015 ; Ipek et al, 2017 ; Sonbarse et al, 2017 ; Aras et al, 2018 ; Arıkan et al, 2018 ). However, the main mechanisms driving such effects are complex and not fully understood.…”

Several Yeast Species Induce Iron Deficiency Responses in Cucumber Plants (Cucumis sativus L.)

“…However, different results obtained using sterile soils have shown that, even with these genotypes, the cooperation of the microorganisms of the rhizosphere is necessary for an adequate Fe acquisition [30,32]. Several studies, carried out with beneficial fungi or bacteria, have shown that its application to soils can improve Fe nutrition in plants [33][34][35][36][37][38][39][40][41]. However, nothing is known to date about the possible role that yeasts may play in the Fe nutrition of plants.…”