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Peach varieties grafted on the rootstock “Nemaguard” (Prunus persica (L.) Batsch) usually show chlorosis when grown in calcareous soils. This chlorosis can be corrected by applying iron chelates to the soil. In this work we present results on the behavior of “Nemaguard” seedlings grown in nutrient solutions with different concentrations of bicarbonate and Fe as FeEDDHA. Chlorosis degree was increased by either increasing bicarbonate (0-15 mM) or decreasing Fe (100-0 μM). Shoot dry weight was decreased in chlorotic plants, but also in green plants grown with bicarbonate (15 mM) and high Fe (100 μM). This indicates that the growth decrease caused by bicarbonate is not only related to Fe deficiency chlorosis. When plants were grown with 10 mM bicarbonate and 2.5 μM Fe and showed clear chlorosis symptoms, they were transferred to a similar nutrient solution but with 100 μM Fe. After one week plant regreening was appreciable, in particular in the youngest leaves.The root Fe(III) reducing capacity was measured in a medium with absence of bicarbonate and in the presence of 10 mM MES, at pH 5.0, for 2h and 30 min. In the treatment with 10 mM bicarbonate and 2.5 μM Fe, roots had a very low reducing capacity and plants became chlorotic. However, these plants markedly increased their reducing capacity just one day after transferring them to a similar nutrient solution but with 100 μM Fe, despite they were still very chlorotic. These results show that bicarbonate inhibits the development of reducing capacity under low Fe conditions but not at higher Fe levels. It is assumed that under field conditions both the induction of chlorosis and the regreening process may be partly consequence of changes in the reducing capacity.

Six sunflower (Helianthus annuus L.) lines were grown in nutrient solution to characterize their sensitivity to bicarbonate-induced Fe chlorosis. Sensitivity was evaluated by chlorosis score and growth reduction relative to the control without added bicarbonate. Chlorosis score was inversely correlated to chlorophyll and Fe concentrations in the uppermost leaves. This technique seems valuable for determining genotypic differences in sensitivity to Fe-induced chlorosis in sunflower. Bicarbonate treatment resulted in an increase in the Ca, Mg, K and Mn and in a decrease in the Fe and P concentrations in leaves. In roots, bicarbonate treatment resulted in a decrease in the Fe and Mn concentrations. Some of the effects of bicarbonate on these elemental compositions were related to the degree of chlorosis.