Phenotypic and Symbiotic Properties of Rhizobia on Some Acacia Species from Silti Zone, Lanfuro Woreda Southern Ethiopia
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Date
2017-08-03
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Addis Ababa University
Abstract
Acacia is a multipurpose leguminous woody plant widely distributed in a wide range of
habitats because of its ability to fix nitrogen and improve soil fertility. However,
effectiveness in nitrogen fixation is variable, due to different factors. In this study, eleven
isolates of root nodule bacteria from four Acacia species were isolated and evaluated for
their effectiveness in nitrogen fixation under greenhouse conditions. The isolates were
characterized based on their morphological, physiological and symbiotic characteristics.
Accordingly, most of the isolates (80%) collected from Acacia abyssinica, Acacia negrii
and Acacia seyal were fast growing rhizobia, whereas root nodule bacteria from Acacia
albdia were slow growers. The isolates showed variations in morphological and
physiological characteristics and most of them were tolerant to high concentration of
NaCl (5-6%) and grew over a wider temperature ranges of (40C-450C) and they were
capable of utilizing various types of carbohydrates. Three isolates of AURAaby21,
AURAaby24 (both from A. abyssinica) and AURAsey41 (from Acacia seyal) were
phosphate solubilizes. The symbiotic effectiveness of the isolates showed significant
(P≤ 0.05) variation in mean shoot dry weight compared to their respective N+ and Ncontrol
groups. The isolates induced nodulation with average nodule number of 34
NN/plant (Acacia albdia) and 52 NN/plant with Acacia seyal, average nodule dry weight
of 0.051 mg/plant (Acacia negrii) and 0.041 mg/p (Acacia abyssinica). The Seedlings
accumulated shoot dry weight of 0.3 g/plant (A. abyssinica) to 0.43 g/plant (Acacia
negrii). Accordingly, more than 70% of the isolates i.e. AURAal 11 (Acacia albdia),
AURAaby22 (A. abyssinica), AURAneg31 (Acacia negrii) and AURAsey41 (Acacia
seyal) induced highly effective, whereas, AURAaby21, AURAaby24 (both from Acacia
.abyssinica), AURAneg32 (Acacia negrii) and AURAsey42 (Acacia seyal) induced
effective nitrogen fixation on their respective host. Some acacia spp. nodulated only with
fast growing rhizobia, while other acacia spp. nodulated only with slow growing rhizobia.
In most case, acacia spp. that nodulated with both fast and slow growing can only
develop an effective symbiotic with one type of symbiont.
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Keywords
Acacia, Rhizobia, Phosphate Solubilization, Salt Tolerance