XVI International Botanical Congess

N2 fixing actinorhizal trees in the family of Casuarinaceae are economically of great interest in tropical and subtropical zones. They usually grow in sandy soils with low fertility by virtue of their ability to fix N2. After evaluating the actual relationships between mycorrhizae and trees of Casuarinaceae, we highlight the possible role of cluster roots as an effective alternative to substitute for mycorrhizae to improve growth of trees in nutrient deficient soils. Fe deficiency, in addition to P deficiency seems to be the major factor inducing the formation of cluster roots in C. glauca and C. cunninghamiana. The effect of N source on cluster root formation is discussed in relation to values of pH in the plant culture solution. Approaches to improve growth of Casuarinaceae trees through use and election of plant species or plant genotypes with high cluster roots-producing potential are suggested.