Diversity, Symbiotic Effectiveness and Plant Growth Promoting Characteristics of Rhizobia and Rhizospheric Bacteria on Growth and Production of White Lupin (Lupinus Albus L.) Under Greenhouse and Field Conditions In North Western Ethiopia
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Date
2018-04-03
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Addis Ababa University
Abstract
White Lupin (Lupinus albus L.) is a traditional legume crop in Ethiopia that can play
complementary or alternative roles as sources of organic fertilizers to replenish nitrogen depleted
soils in farming systems as it forms symbiotic associations with soil bacteria that have atmospheric
nitrogen fixation and other plant growth promoting abilities. This study was aimed to investigate
the diversity and symbiotic effectiveness of rhizobia and rhizobacteria on growth and production
of white lupin (Lupinus albus L.) from major producing areas of the country. A total of 100
bacterial isolates were obtained from the root nodules of White lupin and characterized based on
their phenotypic, biochemical and plant growth promoting characteristics using various standard
methods. Accordingly, 39 isolates were confirmed as rhizobia on the basis of presumptive and
authentication tests. These rhizobial isolates showed wide diversity in their symbiotic and cultural
characteristics as well as heterotrophy, such as C and N-substrates utilization, tolerance to metal
toxicity, antibiotics, pH, salt and temperature. Moreover, some of the isolates showed interesting
PGP traits (IAA, siderophore and HCN production, P solubilization and antagonistic activity
against Fusarium oxysporum) which can make them prior candidates for the production of
inoculants for enhancing White lupin production in the country. Furthermore, the total of 136
phosphate solubilizing bacterial isolates were obtained from rhizospheric soils of White lupin
producing area of the country and 40 effective phosphate solubilizing bacterial isolates were
selected on the basis of their solubilization index (SI). The phosphate solubilizing bacterial isolates
showed variations in their cultural characteristics, doubling times, Gram reactions and C and Nsources
utilization patterns. Quantitative estimation of phosphate solubilizing efficiency of the
phosphate solubilizing rhizospheric bacterial isolates on different inorganic phosphate sources
showed that some of the isolates have better solubilization potential of tricalcium, aluminum and
iron phosphates in Pikosvikya broth upon 5 days of incubation. In addition, they showed good
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tricalcium phosphate solubilization potential under different stress conditions, such as various salt
concentrations, pH and temperature ranges and most of them showed multiple plant growth
promoting characteristics. Furthermore, three rhizobial and two phosphate solubilizing
rhizospheric bacterial isolates that showed better relative symbiotic effectiveness, plant growth
promoting features, stress tolerance and heterotrophic competence were selected to study the effect
of single and co-inoculation on the growth and nodulation of the White lupin under greenhouse
and field conditions. Accordingly, co-inoculated white lupin plants resulted in higher nodule
number, nodule and shoot dry matter accumulation, percent nitrogen and improved relative
symbiotic effectiveness than single rhizobial inoculation, and N-fertilized plants on sand and soil
cultures under greenhouse conditions. Similarly, inoculation of White lupin plants either with the
selected rhizobial isolates alone or co-inoculation of rhizobial and phosphate solubilizing
rhizospheric bacterial isolates showed improved performance on the nodulation, growth and yield
of the crop compared to the negative control under field conditions. In general, the present study
showed that Ethiopian soils contain symbiotically effective White lupin rhizobia and efficient
phosphate solubilizing rhizospheric bacteria with multiple plant growth promoting traits to
enhance growth and production of the crop under natural conditions. However, repeated tests
should be carried out on different field conditions in order to use these rhizobial and phosphate
solubilizing bacterial isolates for inoculant production.
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Keywords
Effectiveness, Lupin, Psrb, Pgp, Rhizobia