Root exudates of grasses improve Fe uptake in a citrus rootstock sensitive to Fe-deficiency

Aim of the present work was to assess the capability of two perennial grasses (Poa pratensis L. and Festuca rubra L.) to improve Fe uptake by the highly-susceptible citrus rootstock citrumelo "Swingle". Citrus plants were unable to induce the physiological responses to Fe-deficiency; however, in these plants uptake of 59Fe from 59Fe-hydroxide could be increased by the presence of Fe-deficient grasses. No beneficial effect was observed with the use Fe-sufficient grasses. A progressive increase in 59Fe uptake by citrus plants was also evident after supplying increasing amounts of DMA, the major phytosiderofore (PS) released by grasses. Re-greening of Fe-deficient citrus plants was obtained by intercropping with grasses in rhizoboxes filled with a chlorosis-inducing calcareous soil; a concomitant increase in the amount of Fe in the leachates was also observed. Data indicate that Fe nutrition of a Fe-inefficient citrus rootstock can benefit from Fe mobilized by PS released by perennial graminaceous species