Symbiotic characterization and diversity of rhizobia associated with native and introduced acacias in arid and semi-arid regions in Algeria

Abstract

The diversity of rhizobia associated with introduced and native Acacia species in Algeria was investigated from soil samples collected across seven districts distributed in arid and semi-arid zones. The in vitro tolerances of rhizobial strains to NaCl and high temperature in pure culture varied greatly regardless of their geographical and host plant origins but were not correlated with the corresponding edaphoclimatic characteristics of the sampling sites, as clearly demonstrated by principal component analysis. Based on 16S rRNA gene sequence comparisons, the 48 new strains isolated were ranked into 10 phylogenetic groups representing five bacterial genera, namely, Ensifer, Mesorhizobium, Rhizobium, Bradyrhizobium, and Ochrobactrum. Acacia saligna, an introduced species, appeared as the most promiscuous host because it was efficiently nodulated with the widest diversity of rhizobia taxa including both fast-growing ones, Rhizobium, Ensifer, and Mesorhizobium, and slow-growing Bradyrhizobium. The five other Acacia species studied were associated with fast-growing bacterial taxa exclusively. No difference in efficiency was found between bacterial taxa isolated from a given Acacia species. The tolerances of strains to salinity and temperature remains to be tested in symbiosis with their host plants to select the most adapted Acacia sp.-LNB taxa associations for further revegetation programs.

Reduced availability of rhizobia limits the performance but not invasiveness of introduced Acacia

“…Compatible rhizobia also appear to be present in many locations where Acacia have been introduced, with species recorded nodulating in Europe (Rodríguez-Echeverría et al 2009), Asia (Midgley & Vivekanandan 1987;Le Roux et al 2009;Ma et al 2012), Africa (Mohamed et al 2000;Joubert 2002;Rodríguez-Echeverría 2010;Boukhatem et al 2012) and the Americas (Aronson, Ovalle & Avendano 1992), as well as outside their native range in Australia (Birnbaum et al 2012). Although it is not clear what facilitates nodulation outside the native range, the widespread occurrence of cosmopolitan rhizobia (Weir et al 2004;Birnbaum et al 2012) and the co-introduction of compatible rhizobia from the native range have both been implicated (Rodríguez-Echeverría 2010; Birnbaum et al 2012;Ndlovu et al 2013).…”

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…Studies of Acacia spp. in Australia and Algeria, where the shrubby legumes dominate many ecosystems where dryland salinity is a major issue, suggested a high phylogenetic bacterial diversity (Thrall et al 2009;Boukhatem et al 2012). Based on 16S rRNA gene sequence comparisons, 48 isolates ranked into 10 phylogenetic groups representing five bacterial genera, namely, Ensifer, Mesorhizobium, Bradyrhizobium and Ochrobactrum (Boukhatem et al 2012).…”

Nodular bacterial endophyte diversity associated with native Acacia spp. in desert region of Algeria

“…In a previous work, we found out (Boukhatem et al, 2012) that there were no relationship between in vitro tolerances of rhizobial strains to NaCl and high temperature and corresponding edaphoclimatic characteristics of the sampling sites. These findings were in agreement with this present study; maximum in vitro strain salinity tolerance was reported for bacterial endophytes originated from slightly saline soil (Oued Idekel) than those from non-saline sites (Table 1 and Figure 2).…”