PHYSIOLOGICAL-RESPONSES OF CLONAL QUINCE ROOTSTOCKS TO IRON-DEFICIENCY INDUCED BY ADDITION OF BICARBONATE TO NUTRIENT SOLUTION

''MA'' quince clonal rootstock is more susceptible to lime-induced chl orosis than clone ''Ct.S.212''. Trials were performed in order to dete rmine whether differences observed between the two clones in calcareou s soil were maintained when iron (Fe)-deficiency was induced by additi on of bicarbonate (HCO3) to a modified Hoagland nutrient solution No 1 . In addition, trials were aimed to verify whether the rootstocks show ed differing physiological responses. Results confirmed that total lea f Fe content was not a suitable tool to screen rootstocks for chlorosi s tolerance. In contrast, ''active'' Fe and chlorophyll content (well correlated with chlorotic symptom levels), together with fresh and dry matter production, were found to be good parameters for genotype eval uation. Total Fe content increased in the root system of stress-grown ''MA'' plants more than in ''Ct.S.212'' root systems. Root Fe3+-reduct ase activity increased in ''MA'' and ''Ct.S.212'' under Fe-deficiency conditions obtained by using an Fe-free solution or by addition of sod ium bicarbonate (10 mM NaHHCO3). In this case, ''Ct.S.212'' showed rou ghly 6-fold increased capacity three hours after the beginning of the assay. This increase was greater than that induced by Fe absence. Clon e ''MA'' showed similar behaviour, but with a lower rate of reduction (3-fold increase in reducing capacity).