Henri Fankem

Maize (Zea mays) growth promotion by rock-phosphate solubilising bacteria isolated from nutrient deficient soils of Cameroon

Rock phosphate is an alternative strategy for less expensive natural sources of plant nutrients. However, this can be efficiently used by plants only when associated with phosphate solubilising microorganisms. Phosphate solubilising bacteria (PSB) from soils of two agro ecological zones of Cameroon were screened for their phosphate solubilising ability on plates and in liquid cultures supplemented with Malian, Moroccan or Mexican rock phosphates. They were subsequently tested on maize grown in pots filled with unsterile soil amended with Malian rock phosphate for their aptitude in promoting maize growth. Under in vitro condition, Enterobacter sp. showed halo zone on plates supplemented with the different rock phosphates with an index of solubilization (IS) varying between 2.10 and 2.71. This strain also showed the highest concentration of mobilized P with all rock phosphates: 1075.17, 1161.04, 862.57 µg P/g for Malian, Moroccan and Mexican rock phosphates, respectively, followed by Klebsiella sp. with the concentrations of 862.57, 615.19, 426.29 µg P/g, respectively. The Malian (402.5 µg P/g) and Moroccan (403.7 µg P/g) rock phosphates appeared to be the easiest phosphates to be solubilised by the different strains. However, the Mexican rock phosphate (345.3 µg P/g) was less solubilised in broth. In general, all the strains in single and in consortia significantly increased the number of leaves, stem base diameter, total dry mass, shoot dry mass and root dry mass as compared to non-inoculated control. The effect of inoculation with single strain varied between 27.5 and 59.3% growth increase, while the effect of inoculation with consortia varied between 54.1 and 109.3% as compared to non-inoculated control. The findings of the current study suggest the potential use of rock phosphate and PSB that would enhance maize productivity in economically profitable and environmentally friendly ways. Key words: Maize growth, phosphate solubilising bacteria, plant nutrient, rock phosphate.

Selecting Indigenous P-Solubilizing Bacteria for Cowpea and Millet Improvement in Nutrient-Deficient Acidic Soils of Southern Cameroon

A trial of a screening and selection strategy for phosphate-solubilizing bacteria based on phosphate solubilization ability, and the subsequent effect of these bacteria on plant growth promotion under in situ conditions, was conducted. Of the 277 (187 from soils and 90 from roots) microorganisms tested, 10 bacteria (BOR8, LEJ14, DR5, DR9, EDJ4, EDJ6, EDJ8, SR7, EMJ5, LR7) were selected. All the bacteria were able to show P dissolution halo zone particularly on agar plates containing sparingly soluble iron phosphate as well as they were able to mobilize important amount of P in liquid media supplemented with either Ca3(PO4)2 or AlPO4·H2O or FePO4·2H2O. Calcium phosphate (Ca-P) solubilization resulted from combined effects of pH decrease and carboxylic acids synthesis. However, the synthesis of carboxylic acids was the main mechanism involved in the process of aluminium phosphate (Al-P) and iron phosphate (Fe-P) solubilization. Both nutrients were mobilized at pH 4 corresponding to their natural occurrence by citrate, malate, tartrate, on much lower level by gluconate and trans-aconitate. Subsequently, a greenhouse trial using cowpea and millet inoculated with selected bacteria showed a significant improvement of plant phosphorus uptake as well as root and shoot dry weight. However, the selection of phosphate-solubilizing bacteria as possible inoculation tools for phosphate-deficient soils should focus on the integral interpretation of laboratory assays, greenhouse experiments, and field trials.

Community structure and plant growth-promoting potential of cultivable bacteria isolated from Cameroon soil

Exploiting native plant growth-promoting rhizobacteria (PGPR) in Cameroonian agro-ecosystems provides a means to improve plant-microbe interactions that may enhance ecosystem sustainability and agricultural productivity in an environmentally eco-friendly way. Consequently, we aimed to investigate the community structure and functional PGPR diversity of maize grown in Cameroon. Native bacteria isolated from Cameroon maize rhizosphere soil were identified by partial 16S rRNA gene sequencing and screened for traits particularly relevant for Cameroon low-fertility soil conditions, such as their abilities to tolerate high concentrations of salt, and their plant growth- promoting potential. Genetic and functional diversity was characterized according to their phylogenetic affiliation. A total of 143 bacteria were identified and assigned to 3 phyla (Actinobacteria, Firmicutes and Proteobacteria), 13 families and 20 genera. Bacillus (31.5%), Arthrobacter (17.5%), and Sinomonas (13.3%) were the most abundant genera identified among all the isolates. Based on their in vitro characterization, 88.1% were salt tolerant at 2% NaCl, but only 16.8% could tolerate 8% NaCl, 50.4% solubilized phosphate, 10.5% possessed the nifH gene, and 19.6% produced siderophores. Six isolates affiliated to the most abundant genera identified in this work, Bacillus and Arthrobacter, carrying multiple or only single tested traits were selected to evaluate their growth- promoting potential in an in vitro maize germination assay. Three strains possessing multiple traits induced significantly increased hypocotyl and root length of maize seeds compared to non-inoculated control seeds. Our results indicate the potential of selected indigenous Cameroon rhizobacteria to enhance maize growth.

Data on molecular identification, phylogeny and in vitro characterization of bacteria isolated from maize rhizosphere in Cameroon

Bacteria, which establish positive interactions with plant roots, play a key role in agricultural environments and are promising for their potential use in sustainable agriculture. Many of these mutualistic bacteria provide benefits to plant hosts by facilitating soil mineral nutrient uptake, protecting plants from biotic and abiotic stresses and producing substances that promote growth. The dataset presented here, is related to the publication entitled “Community structure and plant growth-promoting potential of cultivable bacteria isolated from Cameroon soil” (Tchuisseu et al., 2018) [1]. The data provide an extended analysis of the occurrence, taxonomical affiliation and functional traits of bacterial groups isolated from the rhizosphere of maize in Cameroon at different taxonomical levels, using a combination of molecular/bioinformatics tools and in vitro studies. Bacteria were isolated from maize rhizosphere soil. Isolated bacteria were identified using the 16s rRNA gene sequencing and phylogenetic analyses. All strains were characterized for their potential of salinity tolerance and growth promotion (phosphate solubilization, nifH gene presence and siderophore production) in order to select efficient bacterial strains for designing biological fertilizer exploitable for agriculture under specific stress conditions of the country. The data will be valuable for further studies on plant associated bacteria in Cameroon, which are still largely unexplored.