A New Technique for Screening Iron-Efficient Genotypes in Peach Rootstocks: Elicitation of Root Ferric Chelate Reductase by Manipulation of External Iron Concentrations

The possibility of using the root ferric chelate reductase enzymatic activity as a tool for iron (Fe) efficient rootstock screening in breeding programs has been investigated. Ferric chelate reductase activities were estimated spectrophotometrically from the formation of the Fe(II)–bathophenantroline complex by exposing the roots of intact plants to nutrient solution containing Fe(III)-EDTA. Four micro-propagated peach rootstocks, GF-677, Adesoto (syn. Puebla de Soto), Barrier and Cadaman, known to differ in tolerance to Fe deficiency under field conditions, were grown in hydroponic cultures containing 90 µM Fe(III)-EDTA. After 9 days, plants were grown without any Fe in the nutrient solution for 4 more days. Then, some plants were re-supplied with 45 and 180 µM of Fe(III)-EDTA for 1, 2, or 3 days. A transient increase in root ferric chelate reductase activity was elicited by Fe resupply in GF-677 and Adesoto, two Fe-efficient genotypes, whereas no induction was found in other two genotypes, Barrier and Cadaman, which are known to be Fe-inefficient. Leaf Fe concentrations after resupply were higher in the Fe-efficient genotypes than in the Fe-inefficient ones. These results indicate that the capacity of the roots to reduce ferric compounds could be used as a screening technique for Fe efficiency, provided it is elicited by manipulation of the external Fe levels. This protocol could be easier to use for commercial breeders looking for Fe-efficient rootstock genotypes.