Evaluation of Phyto Beneficial Traits of Indigenous Phosphate Solubilizing Bacteria and Fungi as Microbial Inoculants for Enhancing Growth and Production of Coffee (Coffea Arabica) Under Greenhouse and Field Conditions in Jimma South West of Ethiopia

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Addis Ababa University


Exploitation of phosphate solubilizing bacteria (PSB) and fungi as microbial inoculants is known to promote plant growth through the supply of plant nutrients and supression of pathogens. In view of this, the present investigation was planned to assess the phytobeneficial traits of phosphate solublizing bacterial and fungal isolates recovered from coffee (Coffee arabica) and vermicompost to determine their potential in growth promotion of coffee seedlings under low input agriculture.. The microbes were isolated and purified following standard methods. The selected isolates were investigated for their plant growth promoting properties, eco-physiological tolerance under laboratory conditions, and further tested under greenhouse and nursery experiments. The greenhouse and nursery experiments were conducted with completely randomized design (CRD) in three (3) replications per treatments. Thus, a total of 154 bacteria and 72 fungi isolates were recovered from which twelve potent bacterial and nine fungal isolates were selected and investigated for their plant growth promoting properties. Among the twelve bacterial isolates, three of them were tentatively identified to the genera of Pseudomonas (RCHVCB1) and Bacillus (RScB1.19 and RMaB2.11), and showed significant potential to solubilize Ca3 (PO4)2 and posessed several phytobeneficial traits, viz, indole acetic acid, NH3, HCN productions and N-fixing ability. They also exhibited remarkable tolerance to ecophysiological factors such as heavy metal, acidity and salinity, and inherent antibiotic resistance (IAR). Similarly, three fungal isolates with superior phosphate solubilizeation ability were characterized and identified as genera of Penicillium (RSCF1.19) and Aspergillus (RCHVCF2 and RLVCF2). During co-culture, RSCF1.19 (Penicillium sp.) slightly inhibited the test pathogen, Fusarium xyloriodes. The bacterial (RCHVCB1, RScB1.19, RMaB2.11) and fungal isolates (RSCF1.19, RCHVCF2, RLVCF2) enhanced rate of coffee seed germination under laboratory conditions and promoted coffee seedlings growth under glasshouse conditions. The results of inoculated seeds showed significant (p≤0.05) differences in germination rate and vigor index compared to the control. Isolates RScB1.19, RMaB2.11+RSCF1.19 and RMaB2.11 + RLVCF2 showed high germination rate (20.59%) over the control (13.33%). Moreover, a single inoculation of RLVCF2, RSCF1.19 and co-inoculation of RMaB2.11 with RLVCF2 also showed significant (p≤0.05) mean root length (1.31 cm) and mean shoot length (1.48 cm) over the control. Under greenhouse conditions, single inoculation of RSCF1.19+phosphate and dual inoculation of RSCF1.19 and RCHVCB1 in the presence of inorganic phosphate fertilizer led to significantly higher plant height, root length, stem girth, leaf number, leaf area, fresh and dry weights. Due to high pH value of the potting medium (vermicompost alkaline pH-pH>7.5), all the treatments combined with vermicompost showed suppressive effect and no any seedlings were emerged at all. Under nursery conditions, co-inoculation of RSCF1.19 with three bacterial isolates (RCHVCB1, RScB1.19, and RMaB2.11) in combination with inorganic phosphate led to significantly increase the tested growth parameters. Similar increase in growth attributes was observed in both single and dual inoculations due to vermicompost used compared with both positive and negative controls. Higher NPK-uptake was observed in a combination of bioinoculants and inorganic phosphate fertilizer compared to the positive and negative control. In general, inoculation of RSCF1.19 and RLVCF2 isolates to coffee 74110 variety combined with inorganic phosphate fertilizer resulted in good vigor and healthier coffee seedlings (RSCF1.19, 34.42%) and (RLVCF2, 37.09%) when compared to control (28.49%). Therefore, both RSCF1.19 and RLVCF2 fungal isolates could be used as bioinoculants after field trials in coffee 74110 variety productions.



Bioinoculant, Phosphate, Phytobeneficial, Ecophysiology, Seed Germination, Coffee Seedlings, Coffee Arabica