Iron stress response of three peach rootstock cultivars: Ferric‐iron reduction capacity1

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Abstract
Three peach rootstocks were evaluated for their capacity to reduce ferric‐iron (Fe3+) after iron‐stress treatment. Neither of the rootstocks with tolerance to iron (Fe) chlorosis [Titan1 x Nemaguard (Prunus dulcis (all.) D. A. Webb x Prunus persica (Batsch) L.] nor ‘Montclar’ (P. persica) showed consistently higher Fe‐stress induced Fe3+ reduction/g root fresh weight (RFW) compared to the less tolerant rootstock Nemaguard [(P. persica)]. However, non‐stressed ‘Titan’ x Nemaguard (TNG) showed higher leaf chlorophyll content than both ‘Montclar’ (MC) and Nemaguard (NG) and higher mean Fe3+ reduction by root released reductants than Nemaguard. The reduction rate by root released reductants was approximately 22–34% for NG, 15% for MC, and 29% by TNG. ‘Titan’ x Nemaguard and Montclar maintained better root growth (i.e., had less root necrosis) under Fe‐stress than NG which resulted in greater Fe3+ reduction per plant. This indicates that the maintenance of a greater root surface area during Fe‐stress may be important for the sustenance of significant Fe3+ reduction capacity under prolonged stress on a per plant basis. Fe‐stressed plants of all three rootstocks showed increased formation of root hairs and slightly enlarged root tips, although these died with prolonged Fe‐deficiency in the nutrient solution (after three weeks). Using the Fe2+‐BPDS gel medium procedure, Fe3+ reduction sites were localized at approximately 2–10 mm behind the root tips and on the newly formed lateral roots. Although no differences in Fe3+ reduction at the root surface were seen among rootstocks, Fe3+ reduction in gel medium was more localized and developed earlier in roots of Fe‐stressed plants and those which had nitrogen (N) present in the gel medium as nitrate (NO3‐) only [versus NO3‐ + ammonium (NH4+)].