Performance in nurseries and analysis of native microbial symbionts of Australian Acacia hybrid seedlings in Northern Vietnam (Phu Tho Province)
Abstract
Australian Acacia hybrids (Acacia mangium x Acacia auriculiformis) have been crucial in
Vietnam's afforestation and economic development since 1990. As leguminous trees, their
sustainable and productive growth in poor soils relies crucially on effective microsymbionts in the
soil. Despite considerable attention given to the selection of high-yielding Acacia hybrid clones,
research on their symbionts (including both root-nodule rhizobia and Arbuscular Mycorrhizal
Fungi) has been widely neglected. This oversight has resulted in the suboptimal performance of
Acacia hybrid plantations in Vietnam.
Phu Tho Province, a key province for production of Acacia hybrid clones, provides seedlings to
both Northern and Central Vietnam. Seedlings produced either by tissue culture or cutting
methods were included in the investigation of thirteen private nurseries in the province. Plant
performance, root mycorrhization, nodulation and rhizobia diversity were measured. Interviews
conducted with nursery owners revealed a lack of traceability of the clone origins and intensive
management practices (ie. high rate of mineral fertilizers). Consequently, AMF colonization was
very low (3% to 16%) and nodulation was poor (from 14 to 49 nodules per plant). Despite a low
nodulation, a high genetic diversity among rhizobia was discovered. Surprisingly, clustering based
on restriction fragments length polymorphism (RFLP) of the intergenic spacer region (IGS) did not
align with the seedling type (tissue culture or cuttings), the nursery or the soil characteristics.
Predominant genera of rhizobium discovered from the nodules included Mesorhizobium
(Mesorhizobium sp.), Bradyrhizobium (Bradyrhizobium sp., Bradyrhizobium elkanii, Bradyrhizobium guangdongense) and Rhizobium (Rhizobium tropici). Our study paves the way for further benefits on soil health and plantation productivity of Acacia hybrid in Vietnam by unveiling the potential of effective native rhizobia strain utilization to reduce chemical inputs