RESPONSE TO IRON-DEFICIENCY STRESS OF PEAR AND QUINCE GENOTYPES

Roots of iron (Fe)-efficient dicots react to Fe-deficiency stress by s trongly enhancing the ferric (Fe3+)-reductase system and by lowering t he rhizosphere pH. In this study, we tested whether such adaptation me chanisms characterize pear and quince genotypes known to have differen tial tolerance to calcareous and alkaline soils. Two trials were perfo rmed using micropagated plants of three quince rootstocks (BA29, CTS21 2, and MG), three Pyrus communis rootstocks (OHxF51 and two selections obtained at the Bologna University: A28 and B21) and of two pear cult ivars (Abbe Fetel and Bartlett, own-rooted). In the first trial, plant s were grown in a nutrient solution with [Fe(+)] and without [Fe(-)] F e for 50 days. Their root Fe-reducing capacity was determined colorime trically using ferrozine and FeEDTA, and Fe uptake of Fe(+) plants was estimated. In the second trial, the rhizosphere pH of plants grown in an alkaline soil was measured by a microelectrode. With the only exce ption of pears OHxF51 and A28, whose Fe-reduction rates were similar i n Fe(+) and Fe(-) plants, the Fe-deficiency stress resulted in a signi ficant decrease in Fe reduction. Among the Fe(-) plants, the two pear cultivars, OHxF51 and A28, had a higher Fe-reducing capacity than the quince rootstocks and the cv. Abbe F. When plants were pre-treated wit h Fe, reduction rate was highest in the P. communis rootstocks, interm ediate in the own-rooted cultivars, and lowest in the quinces. Root Fe -reducing capacity of Fe(+) plants proved to be linearly and positivel y correlated with Fe uptake and root proton release. Rhizosphere pH wa s highest in quince MC, intermediate in the other two quinces and in t he cv. Abbe F., and lowest in the pear rootstocks and in the cv. Bartl ett. Our results indicate that roots of pear and quinces do not increa se their ability to reduce the Fe under Fe-deficiency stress. The geno typical differential tolerance to Fe chlorosis likely reflects differe nces in the standard reductase system and in the capacity of lowering the pH at the soil/root interface. The determination of the root Fe-re ducing capacity is a promising screening technique for selecting pear rootstocks efficient in taking up Fe.