Molecular markers reveal low genetic diversity in Casuarina equisetifolia clonal plantations in South China

Abstract

Casuarina equisetifolia is planted extensively in clonally-established coastal shelterbelts in South China. During the last decade, the plantations have been severely attacked by Ralstonia solanacearum bacterial wilt, causing widespread decline and mortality. It has been thought that lack of genetic diversity, both within individual sites and at a regional scale, may render the plantations particularly susceptible to attack. Analysis of samples from 109 separate plantations in three provinces, Hainan, Guangdong and Fujian, using microsatellite molecular markers, revealed that only 22 separate clones are in use. Analysis of co-ancestry among the clones further revealed that many are closely related, consistent with selection of new clones from the sexually-reproduced offspring of existing ones, or selection of multiple clones from individual seedling families. Comparison with wild materials from throughout the species’ natural range indicated that the origins of the South China clones are most likely from within the Southeast Asian region. We recommend diversifying the genetic base of planting material in South China and planting a more-diverse mix of unrelated clones at local and regional scales.