Effects of Acidity on Growth and Symbiotic Performance of Rhizobium leguminosarum bv. viciae Strains Isolated from Faba Bean Producing Areas of Ethiopia

Faba bean is one of the legume crops commonly grown in Ethiopia. It is important source of dietary protein to the majority of population in the country. Soil acidity and related stresses are among the major yield limiting constraints for this crop. This study was conducted with the aim of evaluating acidity tolerance of Rhizobium leguminosarum bv. viciae strains isolated from faba bean growing regions of the country and their symbiotic performance under different acidic conditions. Four strains isolated from root nodules of faba bean were tested for tolerance to acidity in a defined liquid media. The results indicated that none of the tested strains was tolerant to pH 4.0 while two of them (AUFR46 and AUFR100) were found to be tolerant of pH 4.5. When tested at pH 5.0 only one isolate (AUFR58) was sensitive. The results of the present study also showed that all acid tolerant strains were recovered from highly acidic soil (4.8- 5.2) and the acid sensitive strain was isolated from neutral soil. A positive correlation (r= 0.92) was observed between minimum pH tolerated in culture media and pH of origin soil of the strains. Nodulation and nitrogen fixation abilities of these strains were evaluated on sand culture. The results indicated that at pH 4.5 and 5.0 nodulation was totally inhibited and only one isolate (AUFR58) could not be able to induce nodule formation on host plant roots at pH 5.5. The results also showed that acidity (pH 5.5) reduced shoot dry weight, nodules number, total nitrogen at a highly significant level (P<0.01) compared to plants grown at pH 6.5 and 7.0. In pot experiment with soil of different pH, inoculation of the rhizobial strains improved the growth, nodulation and nitrogen content of the plants significantly over the uninoculated controls. Besides, acid tolerant strains showed better performance over acid sensitive strains in acidic soils and thus, they are highly recommended for field test in acidic soil.Keywords: Acidity tolerance; Nodulation; Nitrogen fixation; Vicia faba; Rhizobium; Faba bea

Symbiotic and phenotypic diversity of Rhizobium leguminosarum bv. viciae from Northern Gondar, Ethiopia

Rhizobia that nodulate cool season legumes are widely spread in the Mediterranean and highland agro ecosystems. Faba bean is one of these important crops that represent the major protein source of human nutrition, cash crop for farmers and component of the farming systems. This study is aimed at identifying rhizobia isolates capable of guarantying efficient nitrogen derived from biological nitrogen fixation. Due to this, a total of twenty-one isolates of Rhizobium were isolated from as many sampling sites of northern Gondar using plant infection method. The isolates were characterized morphologically and physiologically and tested on sand and soils to evaluate their symbiotic effectiveness. Studies on symbiotic effectiveness on sand culture indicated that, the strains showed shoot dry matter ranging from 0.4 (AUFR127) to 2.3 g/plant (AUFR124), with negative control (0.2 g/plant) and positive control of 2.4 g/plant. Eighty percent of the isolates were found to be effective and have very effective nitrogen fixers based on their shoot dry matter accumulation (50 to 100%) in relation to the nitrogen fertilized control plants. Culturally, almost all of them displayed large colonies with diameters of 2 to 4.5 mm, generation time of 1.9 to 4.3 h and showed characteristics of fast growing rhizobia. With a few exceptions, isolates grew at temperatures of 15 and 35°C and were found to be sensitive to salt, except AUFR118 that grew up to 5% NaCl. The isolates also grew on a wide range of moderate acidity and alkalinity (pH5.5-9).With the exception of gluconate, citrate and tartarate, almost all isolates grew on all carbohydrates. The pattern of intrinsic antibiotic resistance showed that, almost all of them were tolerant to chloramphenicol, nalidixic acid and erythromycin. Isolates AUFR118, AUFR128 and AUFR132 were found to be resistant to almost all tested antibiotics. These isolates were also included in the effective and very effective symbiotic groups. The trial of the 5 selected effective isolates on two soil types showed that, they performed well without any significant difference on their respective soils. Interestingly, the isolates were found to nodulate the host on the highly acidic soil (pH 4.8) that failed to be nodulated by the indigenous rhizobia. Generally, the present work shows the physiological and symbiotic diversity of the isolates in the traditional agricultural areas of the region and the potential of these rhizobia to be used as effective commercial inoculants in areas where the indigenous rhizobia fail to do so. This will help to reclaim acidic soils for faba bean production.Key words: Faba bean, Northern Gondar, Rhizobium, phenotypic diversity, symbiotic effectivenes

Characterization of Phosphate Solubilizing Faba Bean (Vicia faba L.) Nodulating Rhizobia Isolated from Acidic Soils of Wollega, Ethiopia

Some species of rhizobial bacteria nodulating faba bean are characterized by phosphate solubilization. In order to study their in vitro and symbiotic characteristics, twelve rhizobial isolates nodulating faba bean were collected from acidic soil of Wollega, Ethiopia. Solubilization index of the isolates ranges from 1.25 to 2.10. Mean Generation Time of the isolates were less than 2.34; and growth of isolates on Yeast Extract Mannitol agar with bromothymoleblue media were accompanied by change of color from blue to yellow. AUAVR-51 and AUAVR-52 were the highest in TCP-Solubilizion Index. The two isolates were also recognized as stress tolerant when tested in vitro for extreme temperature, osmotic, acidic pH, intrinsic antibiotics, and acidic-aluminum as compared to the other isolates. However, there was no unique metabolic diversity and specialization of AUAVR-51 and AUAVR-52 isolates with respect to carbon and nitrogen source utilization. On the other hand, isolates AUAVR-51 and AUAVR-52 were characterized by effective and highly effective symbiosis on sterile potted sand growth, respectively. In general, phosphate solubilizing rhizobia nodulating faba bean from acidic soil are fast grower; and their solubilization potential varies. However, the contribution of these isolates as double fertilizer should be tested in the real acidic soil characterized by immobilized phosphorous.Keywords: Faba bean Rhizobial isolates Phosphate solubilization Symbiotic effectivenes

Ending Neglect of older people in the response to Humanitarian Emergencies

Older people make up a significant and growing number of those affected by humanitarian crises, yet they are often not sought out or prioritised within the humanitarian response. Humanitarian agencies, donors, and international bodies neglect older people's health and nutrition. The gaps in knowledge and research about the needs of older people in emergencies are considerable. Older people are not monitored in emergencies and they are not prioritised despite evidence of disproportionate mortality and morbidity in this group. We call for policy changes by humanitarian agencies and donors to ensure that the needs of this vulnerable group are met

Occurrence of fungal diseases of Coffea arabica L. in montane rainforests of Ethiopia

Coffee Berry Disease (CBD), Colletotrichum kahawae, Coffee Wilt Disease (CWD), Gibberella xylarioides and Coffee Leaf Rust (CLR), Hemileia vastatrix are the three major diseases reducing production and consumption of coffee in Ethiopia. A survey was conducted from July to September 2005 for CBD and CWD and from 2003 until 2007 for CLR in montane rainforest coffee areas of Ethiopia to estimate the occurrence and distribution of these diseases. Diseases were prevalent in all the surveyed forest coffee areas of Ethiopia: Harenna, Bonga, Berhane-Kontir and Yayu. Depending on the forest coffee area the mean percent incidence of CBD ranged from 2 to 40 % in general and from 2 to 17.9 % at Berhane-Kontir and Bonga, respectively. The mean incidence of CWD varied from 2.4 % at Berhane-Kontir to 16.9 % at Yayu forest coffee areas. The mean incidence of CLR also varied for instance in 2005 from 32.2 % at Berhane-Kontir to 96 % at Harenna forest coffee areas. The detection of the diseases during our surveys requires an integrated management of major coffee diseases for a sustainable conservation and wise use of coffee in montane rainforests of Ethiopia

Nutritional, eco-physiological and symbiotic characteristics of rhizobia nodulating faba bean (Vicia faba L.) collected from acidic soils of Ethiopia

Characterization of root nodule bacteria is used for selecting and using them as inoculants to improve legume production. To this end, faba bean (Vicia faba L.) rhizobia were isolated from nodules collected from acidic soils of Central and Southern-Western parts of Ethiopia. A total of hundred rhizobial isolates were collected and characterized based upon their nutritional, ecophysiological and symbiotic characteristics. The isolates produced low to copious amount of extracellular polysaccharides (EPS) and attain colony sizes ranging from 2 to 7 mm with generation time ranging 0.75 to 3.9 h. Most of the isolates were grown at different pH levels ranging 4.5 to 7.0 and temperatures between 4 and 45°C. They were also capable of growing on many carbon sources and most of the nitrogen sources, and showed significant variations in resisting different types of antibiotics and heavy metals. Based on symbiotic efficiency (SE), 56% of the isolates were found to be very effective when applied with both Degaga and Dosha varieties. All taken together, two isolates, HUGAVf1 and HUCDVf5 were nutritionally versatile, showed a wide range of tolerance to the stress in many of the ecophysiological characters and very effective symbiotic performance should be utilized in future faba bean inoculants production.Key words: Rhizobium leguminosarum biovar. viceae, antibiotic tolerance, carbon utilization, fast growing, heavy metals, temperature tolerance

Phenotypic, host range and symbiotic characteristics of indigenous soybean nodulating rhizobia from Ethiopian soils

Open Access ArticleSoybean is an exotic crop to Ethiopia and may not necessarily have a specific endosymbiont in the soil. However, since it is a promiscuous host, nodulated by cross nodulating rhizobia, it is likely that some compatible endosymbionts exist from heterologous hosts that could nodulate it with effective nitrogen fixation. This necessitated the search for effective indigenous rhizobia isolates and/or compatible and effective cross-inoculating rhizobia that are already adapted to local conditions. To this end, a total of 67 bacterial isolates were trapped from different soil samples using two soybean varieties (Clark-63K and Awassa-95) and one cowpea variety (Bole), to evaluate their diversity and screen for their symbiotic effectiveness. Accordingly, the majority of isolates (93%) were tentatively categorized into alkali producing slow growing Bradyrhiobium spp. and the others (7%) were fast growing and acid producing rhizobia. The isolates showed differences in utilizing various carbon and nitrogen sources and tolerance to acidity, salinity and temperature. The isolates were also diverse in their inherent antibiotic and heavy metal resistance. All the isolates were able to nodulate soybean variety Clark-63K with significant difference in their capacity to infect and effectively fix nitrogen evidenced from variations in nodulation parameters and shoot dry weights. Accordingly, the isolates induced nodulation with nodule number ranging from 2 to 49 nodules plant-1; nodule dry weight of 16 mg plant-1 to 94 mg plant-1 and shoot dry weight between 585 and 1012 mg plant-1. Using shoot dry weight as an indicator of the relative effectiveness of the isolates, 12% of the isolates were highly effective (SE > 80%) and 88% were effective (SE from 50 to 80%) on soybean. Furthermore, the isolates showed narrow and broad host ranges on four legume species viz., cowpea, mung bean, pigeon pea, and peanut. Accordingly, many isolates (67%) formed nodules with effective nitrogen fixation with cowpea (Vigna unguiculata), pigeon pea (Cajanus cajan) (47%), and on few cases with mung bean (Vigna radiata) showing different level of effectiveness. However, the data showed very narrow host range on peanut (Arachis hypogaea) where, only one isolate formed effective nodules