IRON STRESS-RESPONSE OF 3 PEACH ROOTSTOCK CULTIVARS - FERRIC-IRON REDUCTION CAPACITY

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 ['Titan' 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(+))].