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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Date
2021-12-17
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Addis Ababa University
Abstract
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.
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Keywords
Bioinoculant, Phosphate, Phytobeneficial, Ecophysiology, Seed Germination, Coffee Seedlings, Coffee Arabica