Effects of bicarbonate and iron supply on Fe(III) reducing capacity of roots and leaf chlorosis of the susceptible peach rootstock "Nemaguard"

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 muM) Shoot dry weight was decreased in chlorotic plants, but also in green plants grown with bicarbonate (15 mM) and high Fe (100 muM). 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 muM Fe and showed clear chlorosis symptoms, they were transferred to a similar nutrient solution but with 100 muM 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 muM 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 muM 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.