LUPINUS SPECIES DIFFER IN THEIR REQUIREMENTS FOR IRON

The effect of iron supply on the growth and nodulation of Lupinus angu stifolius L. (Gungurru), Lupinus luteus L. (R-1171) and Lupinus pilosu s Murr. (P20957) was studied in acid solutions. Plants of the three sp ecies were grown together in the same solution and inoculated with Bra dyrhizobium (Lupinus) WU425. Plants were then grown with or without ap plied NH4NO3. The lupin species differed greatly in their sensitivity to low iron concentrations in solution with L. pilosus being most tole rant and L. luteus most sensitive. L. pilosus had the highest iron con centration in tissues and had a higher ratio of iron concentration in the youngest fully expanded leaf blades (YEB) to that in roots than th e other two species. L. luteus had higher iron concentrations in roots but lower iron concentration in YEB and shoots than did L. angustifol ius. The requirements of internal iron for the maximal chlorophyll syn thesis in YEB were 65 mug g-1 for L. angustifolius and L. luteus, and 52 mug g-1 for L. pilosus. In contrast to effects on growth, the three species had similar external iron requirements for nodule formation i n roots and for maximal nitrogen concentrations in shoots. The results indicate that iron tolerant lupin species require lower internal and external iron supply and have a greater ability than sensitive species to translocate iron from roots to shoots.