PHYTOSIDEROPHORE RELEASE RELATED TO SUSCEPTIBILITY OF WHEAT TO IRON-DEFICIENCY

Some wheat (Triticum aestivum L. emend, Thell.) genotypes when grazed by livestock and subsequently used for grain production develop Fe def iciency chlorosis and decline in grain yield. Wheat is known to releas e phytosiderophores (compounds involved in Fe mobilization and uptake) in response to Fe deficiency stress. These studies conducted in envir onmental growth chambers correlated the release of phytosiderophore fr om the roots of eight wheat genotypes with field chlorosis scores from Oklahoma grazing trials. Plants were grown hydroponically in low Fe n utrient solutions and phytosiderophore release was measured with an Fe -binding assay, Since grazing exacerbates Fe deficiency chlorosis deve lopment, the eight genotypes were tested both with and without clippin g. Phytosiderophore release with time was summed to improve correlatio n compared with individual daily measurements. The field chlorosis sco res and the sum of the first six phytosiderophore release measurements (Days 6 to II after imposition of low Fe treatment) from unclipped wh eat were not correlated (r = -0.17, P = 0.70), but the sum of the Last five days (13 to 17) was highly correlated with field chlorosis score s (r = -0.82, P = 0.01). Clipping did not greatly improve the relation ship (r = -0.83, P = 0.008). Correlation coefficients were more consis tent for individual days when plants were clipped, Three-day sums of p hytosiderophore release provided good correlations when data were coll ected in the latter stages of Fe deficiency development (Day II). Iden tification of chlorosis resistant lines by monitoring phytosiderophore release will by-pass years of field trials and should be implemented by plant breeders where wheat is managed concurrently for forage and g rain production on calcareous soils.