Diriba Muleta

Legume Responses to Arbuscular Mycorrhizal Fungi Inoculation in Sustainable Agriculture

Currently, the sustainability of ecosystems is in danger due to both application of varied degrading agents and intensive exploitation of tropical forests. During the last decades, inventories of the soil’s productive capacity indicate severe degradation and loss of arable lands. The situation is highly exacerbated in economically disadvantaged countries. The ever increasing human populations prompt extensive usage of agrochemicals to attain optimum yields. The use of such chemicals leads to losses in soil fertility, and hence, requires an alternative to boost crop productivity while sustaining ecological quality. Globally, there is widespread interest in the use of legumes due to their multifaceted functions. It is a well established fact that legumes are essential components in natural and managed terrestrial ecosystems. The arbuscular mycorrhizal fungi (AMF) are universal and ubiquitous rhizosphere microflora forging symbiosis with plethora of plant species and acting as biofertilizers, bioprotectants, and biodegraders. The arbuscular mycorrhizal-legume symbiosis is suggested to be the ideal solution to the improvement of soil fertility and the rehabilitation of arid lands. The voluminous literature has revealed that AMF improve the overall growth of leguminous plants growing under diverse agroecological zones. Furthermore, the tripartite symbiosis between legume–mycorrhizal–rhizobium has shown superior improvements in legumes. In this chapter, attention is paid to association of AMF with leguminous plants and effect of composite inoculation of legume plants with mycorrhizal fungi and rhizobia under different growth conditions. Furthermore, mycorrhizal dependency of legumes, effects of arbuscular mycorrhizal fungi on productivity of legumes with special emphasis on alleviation of environmental stresses, and rehabilitation of desertified and/or degraded habitats is described.

Characterization of rhizobacteria isolated from wild Coffea arabica L.

Rhizobacteria from wild Arabica coffee populations (Coffea arabica L.) in southwestern Ethiopia were isolated and characterized. The main purpose was to identify coffee‐associated rhizobacteria and evaluate their potential in synthesizing the phytohormone indole acetic acid (IAA) and in degrading the ethylene precursor 1‐aminocyclopropane‐1‐carboxylate (ACC). A total of 878 bacterial isolates were screened, of which 395 (45%) isolates were preliminarily characterized using metabolic identification kits (API). Both Gram‐negative and Gram‐positive bacteria were isolated, with the former group predominating (63% of cases). Based on pre‐screening results of the biochemical tests, 51 of the isolates were subjected to PCR‐RFLP (Restriction Fragment Length Polymorphism) analysis that yielded ten groups, of which 24 isolates were identified by 16S rRNA gene sequencing. The major genera identified were Pseudomonas (six species) and Bacillus (four species). Single species of Erwinia, Ochrobactrum and Serratia were also identified. The Erwinia sp., Serratia marcescens and many Pseudomonas spp. produced IAA, and some isolates (all Pseudomonas spp.) were also able to degrade ACC. Several of the microbes found in association with wild Arabica coffee bushes have potential agronomic importance, like e.g. Bacillus thuringiensis, which deserve further testing. According to these in vitro studies, isolates of Erwinia, Serratia and Pseudomonas are of particular interest in inoculant development due to their plant growth promoting traits.

Phosphate Solubilization Potential of Rhizosphere Fungi Isolated from Plants in Jimma Zone, Southwest Ethiopia

Phosphorus (P) is one of the major bioelements limiting agricultural production. Phosphate solubilizing fungi play a noteworthy role in increasing the bioavailability of soil phosphates for plants. The present study was aimed at isolating and characterizing phosphate solubilizing fungi from different rhizospheres using both solid and liquid Pikovskaya (PVK) medium. A total of 359 fungal isolates were obtained from 150 rhizosphere soil samples of haricot bean, faba bean, cabbage, tomato, and sugarcane. Among the isolates, 167 (46.52%) solubilized inorganic phosphate. The isolated phosphate solubilizing fungi belonged to genera of Aspergillus (55.69%), Penicillium spp. (23.35%), and Fusarium (9.58%). Solubilization index (SI) ranged from 1.10 to 3.05. Isolates designated as JUHbF95 (Aspergillus sp.) and JUFbF59 (Penicillium sp.) solubilized maximum amount of P 728.77 μg·mL−1 and 514.44 μg mL−1, respectively, from TCP (tricalcium phosphate) after 15 days of incubation. The highest (363 μg mL−1) soluble-P was released from RP with the inoculation of JUHbF95 in the PVK broth after 10 days of incubation. The present study indicated the presence of diverse plant associated P-solubilizing fungi that may serve as potential biofertilizers.

Effects on Glomus mosseae Root Colonization by Paenibacillus polymyxa and Paenibacillus brasilensis Strains as Related to Soil P-Availability in Winter Wheat

Greenhouse experiments were conducted to assess the effects of inoculating winter wheat (Triticum aestivum) with plant growth promoting rhizobacteria (PGPR) of the genus Paenibacillus under phosphate P-limited soil conditions in the presence or absence of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae. Four P. polymyxa strains and one P. brasilensis strain were compared at two cell concentrations (106 and 108 cells g−1 seeds) of inoculation, and surface sterilized AMF spores were added to pots. Mycorrhizal root colonization, plant growth, and plant uptake of phosphorus were analyzed. Bacterial phosphate solubilization was examined separately in vitro. Most P. polymyxa strains, isolated from wheat, had dramatic effects per se on root growth and root P-content. No treatment gave significant effect on shoot growth. AMF root colonization levels and total plant uptake of P were much stimulated by the addition of most P. polymyxa strains. The AM fungus alone and the P. brasilensis, alone or in combination with the fungus, did not affect total plant P-levels. Our results indicate that practical application of inoculation with plant host-specific rhizobacteria (i.e., P. polymyxa) could positively influence uptake of phosphorus in P-deficient soils by wheat plants, provided that suitable AM fungi (e.g., G. mosseae) are present.

Importance of Arbuscular Mycorrhizal Fungi in Legume Production Under Heavy Metal-Contaminated Soils

Degradation and loss of arable lands have attracted attention of the scientists worldwide to protect lands from further declining. The multifaceted functions of legumes on the other hand in the improvement of natural and managed terrestrial ecosystems have necessitated their sustainable production. Leguminous crops are the important protein source in human dietary systems particularly in developing countries. The legume productions have, however, been seriously hampered due to heavy metal contamination of soils. Maintenance of soil quality adopting various remediation strategies including biological approaches is therefore important. Mycorrhizoremediation among bioremediation has currently been the focus of research. Arbuscular mycorrhizal fungi (AMF) establish mutual symbioses with the majority of higher plants and after colonization, contribute to the plant growth in metal-contaminated sites by increasing plant access to P, by improving soil quality, and by restricting the movement of metals within plant tissues. Here, we have focused to understand on how the heavy metals affect legumes and the incidence of AMF in metal-polluted sites. In addition, the role of AMF in restoring heavy metal-contaminated sites is described. Understanding the role of mycorrhizae in metal detoxification is likely to improve the agronomic strategies in order to take full advantage of mycorrhizal association for legume production in disturbed cropping locations.

Current status of coffee berry disease (Colletotrichum kahawae Waller & Bridge) in Ethiopia

Abstract The current status of coffee berry disease (CBD) caused by Colletotrichum kahawae was intensively assessed and examined in 152 sample coffee farms from 22 districts across major coffee growing regions of Ethiopia. The results showed that CBD was prevalent with significantly (p < 0.001) varied intensity of damage among fields, districts and zones. The highest disease incidence of 70.7, 65.3 and 59.3% was recorded in Hararghe, Gedeo and Jimma, with correspondingly higher severity of 42.7, 46.7 and 32.0%, respectively. The national average incidence and severity of CBD was 52.5 and 29.9% that indicated the present status of the disease is remarkably on increasing trend. The increased intensity of CBD was strongly associated with reduced disease management practices (r = 0.50), altitude (r = 0.42), coffee cultivars (r = 0.23) and production systems (r = 0.28). This empirical evidence shows that CBD is on an upsurge and remains a major challenge to Arabica coffee production in Ethiopia.

Isolation and Molecular Identification of Lactic Acid Bacteria Using 16s rRNA Genes from Fermented Teff (Eragrostis tef (Zucc.)) Dough

Injera is soft fermented baked product, which is commonly prepared from teff (Eragrostis tef (Zucc.)) flour and believed to be consumed on daily basis by two-thirds of Ethiopians. As it is a product of naturally fermented dough, the course of fermentation is done by consortia of microorganisms. The study was aimed at isolating and identifying some dominant bacteria from fermenting teff (Eragrostis tef) dough. A total of 97 dough samples were collected from households, microenterprises, and hotels with different fermentation stage from Addis Ababa. The bacterial isolates obtained from the fermenting teff dough samples were selected on the basis of their acid production potentials. A total of 24 purified bacterial isolates were found to be Gram-positive (they are coccus and rod under microscope) and were good acid producers. Genomic DNA of bacterial isolates were extracted using Invisorb® Spin DNA Extraction kit. 16S rRNA of bacterial isolates were amplified using the bacteria universal primers (rD1 and fD1). The amplified product was sequenced at Genewiz, USA. Sequence analysis and comparison with the resources at the database were conducted to identify the isolated microbes into species and strain levels. The bacterial isolates were identified as Lactobacillus paracasei, Lactobacillus brevis, Enterococcus durans, Enterococcus hirae, Enterococcus avium, and Enterococcus faecium. All identified lactic acid bacteria were able to produce acid at 12 h time of incubation. This study has confirmed the presence of different bacterial species in the fermenting teff dough and also supports the involvement of various groups of bacterial species in the course of the fermentation.

Potential Applications of Some Indigenous Bacteria Isolated from Polluted Areas in the Treatment of Brewery Effluents

Biological wastewater treatment is economically feasible and ecofriendly. This study was aimed at isolating bacteria from brewery wastes and evaluating their bioremediation potential as individual isolate and/or their consortium in reducing the pollutants of brewery effluents. A total of 40 bacterial isolates were recovered and of these the three best isolates were selected. The selected bacteria were identified to genus level by using morphological and biochemical characteristics. Accordingly, the isolates were identified as Aeromonas sp., Pseudomonas sp., and Bacillus sp. After 12 days of incubation, the removal efficiency of these three isolates and their combinations for biological oxygen demand and chemical oxygen demand varied from 73.55% to 94.85% and 76.78% to 93.25%, respectively. Total nitrogen and phosphorus removal was within the range of 54.43% to 77.21% and 41.80% to 78.18%, respectively. Total suspended solid, total solid, and total dissolved solids removal ranged from 66.74% to 90.3%, 54.69% to 88.5%, and 53.02% to 88.2%, respectively. The pH and electrical conductivity values ranged from 6.81 to 8.65 and 3.31 mS/cm to 3.67 mS/cm, respectively. The treated effluent increased Beta vulgaris seeds germination from 80% to 100%, with mean germination time of 3.1 to 5.2 days and seedlings length of 2.3 cm to 6.3 cm. Therefore, the development of this finding into a large scale offers an attractive technology for brewery waste treatment.

Management of post-harvest fruit spoilage fungi by some potential spice extracts

The experiment was carried out to evaluate the antifungal potential of aqueous and ethanolic extracts of four spices (Allium sativum, Zingiber officinale, Cinnamomum zeylanicum and Capsicum annuum) against the important post-harvest spoilage fungi isolated from diseased fruits. In total, 276 isolates of post-harvest spoilage fungi were isolated from four different fruit types (Persea americana, Musa acuminata, Citrus sinensis and Lycopersicon esculentum), out of which 183 isolates were identified while 93 isolates were remain unidentified. The most dominant post-harvest spoilage fungus was Rhizopus sp. (26.45%), followed by Penicillium sp. (19.93%), Aspergillus sp. (10.86%) and Fusarium sp. (9.06%). Results of disc diffusion assay showed that ethanolic extract of C. zeylanicum was found to be most effective against Penicillium sp., followed by aqueous extracts of A. sativum. The ethanolic extract of C. zeylanicum in agar amended assay and minimal inhibitory concentrations were found to be very efficient (100% inhibition) against all the tested fungi. Results of in vivo study showed that pre-inoculated C. zeylanicum ethanolic extract and A. sativum aqueous extract were found effective in reducing the disease severity (6.24–13.67%) and (7.91–13.15%) against the Penicillium, Rhizopus, Aspergillus and Fusarium sp.