Symbiotic Properties of Rhizobium from Crotalaria Ocroleuca Used for Intercropping in Coffee Plantations in South-West Ethiopia
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Date
2017-08
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Addis Ababa Universty
Abstract
It has been established that the symbiosis between Rhizobium and legumes are a cheaper and
usually more effective agronomic practice for ensuring an adequate supply of nitrogen for
legume based crop and pasture production than the application of nitrogen fertilizer.
Crolotalaria ocroleuca is one of the members of crotalaria grown as cover crop or inter crop
in southern and south western parts of Ethiopia. Nineteen isolates were isolated from the
root nodules of Crolotalaria ocroleuca from coffee growing area in Godere Wereda,
Gambella region under Teppi Coffee plantation Enterprise. Presumptive tests and
microscopic features confirmed that the isolates were rod shaped and gram-negative
rhizobia. Based on colony and growth characters the isolates were grouped into two groups.
Accordingly, 15 isolates were fast growing and acid producing Rhizobium spp; whereas four
isolates (AAUCR4.AAUCR9, AAUCR14 and AAUCR18) were slow growing and alkali
producing Brady rhizobium spp. Most of the isolates utilized the carbohydrates; sorbitol,
xylose, and lactose, whereas only 26% and 15% were able to utilize starch and Na-citrate,
respectively. All isolates were resistant to kanamycin and erythromycin at lower
concentration of 2.5 and 5 μm/ml. Only 68% and 79% were résistance at (2.5 μm/ml) and
63% and 16% of the isolates were resistant at (5 μm/ml) to neomycin and gentamycin,
respectively whereas isolates (AAUCR9 and AAUCR18) were resistant to all the tested
antibiotics. The isolates also showed variability in their physiological characteristics. All
isolates grew at 300C .while, 63% and 53% of the isolates were able to tolerate 150C and
400C respectively. All isolates were able to grow at lower salt concentration (1-2%), and five
isolates (26%) showed tolerance up to 4%. Only isolate (AAUCR9) was considered highly
osmo-tolerant since it grew at 5% of salt concentration. Amongst the isolates, 21% were able
to form clear zones around their colonies on Pikovaskaya’s medium and hence, they were
considered as phosphate solubilisers with solubilisation index ranging from (2.2 -3). Relative
effectiveness of the isolates was calculated by dry mass of the inoculated plant over the dry
mass of positive control has significant difference within and among the treatment and
positive and negative control at (p<0.05 Tukey’s test HSD) and accordingly, 47%, and 32%,
of the isolates (79%) were highly effective (80-100%), and effective (50-80%) in nitrogen
fixation. Generally, with over all competency analysis measurement two isolates AAUCR9
and AAUCR18 were the best isolates in terms of effective nitrogen fixation and tolerance to
various ecological features that could make them competent against prospective candidates
under field conditions.
Key words: cultural characters, Gambella, IAR, pH tolerance, symbiotic effectiveness
Description
Keywords
Cultural characters, Gambella, IAR, pH tolerance, Symbiotic effectiveness