Symbiotic Status of Two Protected Forests of Acacia nilotica Var. tomentosa in the Senegal River Valley.

Soil from two protected forests of Acacia nilotica var. tomentosa, located in the Senegal River Valley, was sampled to assess their rhizobial and mycorrhizal status. Forty-one soil samples (0.5 kg each) were collected at 10-15 cm depth in the rhizosphere of Acacia in the two protected forests of Diarra and Lam Nadie (26 and 15 samples, respectively). Soil extracts were used to test rhizobial nodulation of in-vitro growing seedlings of two varieties of A. nilotica, var. tomentosa and var. adansonii. Arbuscular mycorrhizal (AM) fungi soil infectivity was estimated by the most probable number (MPN) method using Acacia nilotica var. tomentosa as test plant. In the Diarra forest, eight soil samples of the 26 tested contained indigenous rhizobial strains nodulating both A. nilotica var. adansonii and A. nilotica var. tomentosa, whereas only one from Lam Nadie contained rhizobial strains. Fifty-six strains were isolated, purified, and their infectivity and efficiency tested on Acacia nilotica var. tomentosa after 60 days of culture under controlled conditions. Strains ND37 from Diarra and NL2 from Lam Nadie are the more effective in terms of shoot and root dry weight. The estimation of the number of viable propagules using the MPN method showed some significant differences between the populations of AMF of Diarra, which was high, and that of Lam Nadie, which was very low. The percentage of colonization of Acacia nilotica var. tomentosa was correlated with the MPN values. These results are discussed with regards to the state of forests. [ABSTRACT FROM AUTHOR]