Technical Abstract: Iron acquisition in pea, as well as in other dicots and the non-grass monocots, involves a two-step iron reduction and transport process referred to as Strategy I. The root iron reductase in pea (designated FRO1) is a plasmalemma-localized protein that reduces rhizospheric ferric iron (usually as Fe[III]-chelates) to ferrous iron, prior to the membrane uptake of ferrous iron through the divalent metal transporter, RIT1. Thus, the iron reductase is an important regulator of whole-plant iron status, especially under alkaline soil conditions where available iron is limiting. It also is a potential breeding target for the development of improved cultivars that would be less susceptible to conditions of iron deficiency stress. Because of our interest in this gene, we wished to map the FRO1 locus in pea, and therefore developed a FRO1-specific CAPS marker that could be used with the JI1794 x Slow mapping population. Over 1,000 segregating markers have been mapped in this recombinant inbred population, permitting new markers/loci to be located with high precision. Our use of the FRO1 marker allowed us to map this locus to the lower arm of linkage group IV (LGIV) in Pisum sativum. The location of FRO1 near the distal end of the non-satellite arm of LGIV makes this gene an important anchor marker for this region of the pea linkage map, because few markers are currently available in this region.