Phenotypic And Symbiotic Properties Of Rhizobia On Some Acacia Species From Silti Zone Lanfuro Woreda Southern Ethiopia

Acacia is a multipurpose leguminous woody plant widely distributed in a wide range ofrnhabitats because of its ability to fix nitrogen and improve soil fertility. However,rneffectiveness in nitrogen fixation is variable, due to different factors. In this study, elevenrnisolates of root nodule bacteria from four Acacia species were isolated and evaluated forrntheir effectiveness in nitrogen fixation under greenhouse conditions. The isolates wererncharacterized based on their morphological, physiological and symbiotic characteristics.rnAccordingly, most of the isolates (80%) collected from Acacia abyssinica, Acacia negriirnand Acacia seyal were fast growing rhizobia, whereas root nodule bacteria from Acaciarnalbdia were slow growers. The isolates showed variations in morphological andrnphysiological characteristics and most of them were tolerant to high concentration ofrnNaCl (5-6%) and grew over a wider temperature ranges of (40C-450C) and they wererncapable of utilizing various types of carbohydrates. Three isolates of AURAaby21,rnAURAaby24 (both from A. abyssinica) and AURAsey41 (from Acacia seyal) werernphosphate solubilizes. The symbiotic effectiveness of the isolates showed significantrn(P≤ 0.05) variation in mean shoot dry weight compared to their respective N+ and Ncontrolrngroups. The isolates induced nodulation with average nodule number of 34rnNN/plant (Acacia albdia) and 52 NN/plant with Acacia seyal, average nodule dry weightrnof 0.051 mg/plant (Acacia negrii) and 0.041 mg/p (Acacia abyssinica). The Seedlingsrnaccumulated shoot dry weight of 0.3 g/plant (A. abyssinica) to 0.43 g/plant (Acaciarnnegrii). Accordingly, more than 70% of the isolates i.e. AURAal 11 (Acacia albdia),rnAURAaby22 (A. abyssinica), AURAneg31 (Acacia negrii) and AURAsey41 (Acaciarnseyal) induced highly effective, whereas, AURAaby21, AURAaby24 (both from Acaciarn.abyssinica), AURAneg32 (Acacia negrii) and AURAsey42 (Acacia seyal) inducedrneffective nitrogen fixation on their respective host. Some acacia spp. nodulated only withrnfast growing rhizobia, while other acacia spp. nodulated only with slow growing rhizobia.rnIn most case, acacia spp. that nodulated with both fast and slow growing can onlyrndevelop an effective symbiotic with one type of symbiont.

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