Monoxenic nodulation process of Acacia mangium (Mimosoideae, Phyllodineae) by Bradyrhizobium sp.

Acacia mangium Willd., a native tree in Australia and Papua New Guinea, has been introduced to countries in Asia and South America where plantations have been established that cover several hundred thousand ha. The present study investigated the early stages of the nodulation process in using an homologous Australian strain. After optimizing the axenic nodulation, histological and cytological studies were conducted using light and electron microscopy. These documented the proliferation of the lysis of mucilage at the root surface, root hair deformation and initiation, as well as the development and growth of multiple infection threads. A belt of tannin-filled cells was shown to surround the central nodular fixation zone. The nodules were of the indeterminate type and the bacteroids had a rod shape, without size modification and with few polyhydroxybutyrate (PHB) granules. Several bacteroids can share the same symbiosome. exhibits both classical and novel features in its nodulation