Phytosiderophore Exudation from the Roots of Iron Stressed Kentucky Bluegrass.

Many Kentucky bluegrass (Poa pratensis L.) cultivars are susceptible to iron (Fe) deficiency chlorosis when grown on calcareous soils and are routinely treated with Fe fertilizers. Aesthetics could be improved and this costly practice could potentially be eliminated with the use of cultivars resistant to Fe deficiency. Grasses are known to release phytosiderophore into the rhizosphere to dissolve Fe for plant use, and this characteristic has been used to screen for resistant cultivars with other species. A chelator-buffer hydroponic study was conducted to stress Baron, Award, Limousine, and Rugby II cultivars at 1 and 10 µM Fe in complete nutrient solution buffered at pH 7.4. Shoot and root Fe concentration and dry matter yields were significantly greater at 10 than 1 µM Fe for all cultivars. The cultivars other than Baron had similar and consistent increases in chlorosis at 1 µM Fe and nearly no chlorosis at 10 µM Fe. Baron was significantly different than the other cultivars in that it developed chlorosis earlier and more severely at both levels of Fe, although chlorosis at 10 µM Fe was not as severe as 1 µM Fe for this cultivar. In addition, Baron exhibited re-greening at the 10 µM Fe concentration. Phytosiderophore exudation was significantly greater for all cultivars at 1 than at 10 µM Fe. Surprisingly, the apparently Fe chlorosis susceptible Baron cultivar not only released phytosiderophore, but released it at a significantly higher level than the other cultivars. These results imply that Fe deficiency susceptibility in Kentucky bluegrass may be related to inefficient uptake mechanisms rather than production and release of phytosiderophore.