DIFFERENTIAL EFFECT OF SOIL-TEMPERATURE ON IRON-DEFICIENCY CHLOROSIS IN SUSCEPTIBLE AND RESISTANT SUBCLOVERS

Iron deficiency, which is most prevalent on calcareous soils, reduces the productivity of susceptible clovers (Trifolium spp.). Factors caus ing differences in Fe-deficiency chlorosis susceptibility among clover cultivars and species are not well understood. The objective of this study was to determine the influence of soil temperature on chlorosis expression, plant growth, and mineral nutrition of Fe-deficiency chlor osis susceptible and resistant cultivars of subterranean clover (T. su bterraneum L.; subclover). Two cultivars of subclover, 'Karridale' (su sceptible) and 'koala' (T. brachycalycinum Katzn. and Morley; resistan t), were grown in a greenhouse on a low-Fe Parrita soil (pH 8.2, claye y, mixed, hyperthermic, shallow Petrocalcic Paleustoll) using a Coneta iner (Stuewe and Sons, Inc., Corvallis, OR) culture system with seven soil temperature treatments within the range of 7 to 33 degrees C. Kar ridale was more chlorotic at low or high soil temperatures than at an intermediate temperature, while the chlorosis of Koala changed only sl ightly with change of soil temperature. Cultivar difference in chloros is was greatest at low soil temperature. Shoot dry weight and number o f root nodules were higher at intermediate soil temperatures than at l ow temperatures for both cultivars. Koala had higher values (P < 0.05) of shoot and root dry weight and number of root nodules than did Karr idale. Shoot Fe concentration of Koala was greatest at intermediate so il temperature, whereas Karridale exhibited less dependence on tempera ture. These results indicate that soil temperature affects the differe ntial expression of Fe-deficiency chlorosis between subclover cultivar s and that low soil temperatures can be used to improve screening for Fe-deficiency chlorosis resistance of subclover.