Acacia senegal (L.) Wild. Associates with a Diversity of Beneficial Micro-symbionts in the Arid and Semi-arid Lands of Kenya

Aims: To determine the populations and diversity of beneficial microsymbionts (rhizobia and mycorrhiza) which associates with Acacia senegal varieties at selected sites in semi-arid areas of Kenya.

Place and Duration of Study: Kenya Forestry Research Institute (KEFRI) Biotechnology Laboratories and selected semi-arid sites of Kenya, between 2009 and 2010.

Methodology: We estimated rhizobia populations, identified mycorhiza abundance and diversity and estimated plant growth of A. senegal plants grown in soils collected from the selected semi-arid sites.

Results: Rhizobia populations were generally low, below 30 cells.g-1 soil, in most of the sites but were relatively higher in areas with high forest cover such as Kimalel (559 cells.g-1 soil) and Ntumburi (104 cells.g-1soil). Seven mycorrhizae species were identified in the selected sites and all the species were represented in all selected sites except Gigaspora spp which was totally absent in Baringo and poorly represented in all sites. Glomus etunicata and Glomus intra were the most abundant mychorrhizal species, and were most abundant in Baringo, at Kimalel (76.7% and 58.3%, respectively) and Rimoi (54.7% and 44.7%, respectively). The same species were also abundant at Daaba (26.3% and 55.7%, respectively) in Isiolo. In overall, mychorhiza were most abundant in Baringo, where Kimalel had in overall highest numbers (20.2%), followed by Isiolo where Daaba had in overall highest mychorrhizal number (13.8%) and finally Kajiado, where Kajiado sub-site had higher mycorhizal number (4.8%) compared to the Namanga sub-site (3.3%). It was established that mycorrhiza survived in harsher conditions (Daaba) than rhizobia.

Conclusions: We concluded that drylands of Kenya have low rhizobia populations, implying need for rhizobia inoculation to enhance rhizobia benefits in A. senegal tree species. We also concluded that the drylands have diverse and abundant mycorrhiza species which vary across sites, and which can be utilized for enhanced mycorrhizal benefits.