Abstract

The Genus Casuarina is a coastal plant distributed throughout South East Asia, Australia, and the Pacific islands. In Taiwan, more than 10 species of Casuarina have been introduced based on the proposition that these drought tolerant, fast growing trees would be suitable for windbreaks and would help stabilize coastal sand. The genetic diversity of three Casuarina species grown in Taiwan, Casuarina equisetifolia, C.glauca, and C. cunninghamiana was determined and compared to those of native populations grown in Australasia as part of an international provenance test using the Inter-Simple Sequence Repeat (ISSR) marker system. Based on our results, the average Nei gene diversity of Casuarina grown in Taiwan (0.1940) is considerably higher (p < 0.001) than that of native populations of C. equisetifolia (0.1288), C. cunninghamiana (0.0922), and C. glauca (0.0577). Cluster and principal component analyses indicated that the Taiwan-grown trees are more closely related to C. equisetifolia than either C. cunninghamiana or C. glauca. By integrated reasoning of  genetic variation and branchlet morphology, we may conclude that coastal Casuarina plants currently survived and grown in Taiwan are the products of introgressive hybridization involving C. equisetifolia, C. glauca, and possibly C. cunninghamiana.

Key words: Casuarina, genetic diversity, hybridization, inter simple sequence repeat (ISSR).