Abstract
This study was initiated to isolate and characterize indigenous rhizobia nodulating faba bean, and evaluate symbiotic characteristics between the crop and the rhizobia in major faba bean producing areas in Tigray highlands. Field crops were also surveyed for nodulation in selected sites of seven (7) faba bean growing districts. A total of 44 rhizobial strains were isolated and their symbiotic properties (nodule number, fresh weight, color and plant growth) were recorded. A total of 12 strains with good symbiotic properties were characterized for their morphological and physiological traits on Yeast Extract Manitol Agar (YMA) medium. The result of the study showed the presence of diversity in morphological, physiological and symbiotic properties among the rhizobial strains. There was statistically significant difference in nodule number, fresh weight and shoot height (p< 0.05) and great variation in nodule color within and among the districts. Nodulation status of the field crops was poor except Ofla, D/Temben and Alaje districts. Though the presence of diversity among the strains revealed the possibility of getting potentially effective adaptable rhizobial strains that enhance faba bean productivity, the weak symbiotic properties observed during isolation and nodulation status survey might partly be responsible for yield variation and reduction in low input cropping systems of Tigray. Hence, studies on a need for inoculation and factors responsible for poor nodulation need to be undertaken to realize the role of biological nitrogen fixation in Tigray cropping systems. Key words: Biological nitrogen fixation, Faba bean, Nodulation, Rhizobia, Symbiotic Effectiveness, Tigray.
Highlights
It serves as a daily food and as cash crop in many parts of the country (Hawitin and Hebblewaite, 1993). This legume crop is known for its ability to form endosymbiotic association with root nodulating bacteria group called Rhizobium leguminosarum bv
The effect of BNF vary depending on survival of the rhizobial strains under different soil conditions like salinity, drought, acidity, soil temperature (Zaharan, 1999)
Exploiting BNF can be one of the alternatives to enhance soil fertility in Tigray considering the severe land degradation, and unavailability and unaffordability of commercial fertilizers for resource poor farmers. This reflects the need to study the effect of indigenous rhizobia on nodulation and growth of faba bean to fully realize the role of BNF
Summary
Ethiopia is one of the largest faba bean producing countries in the world only second to China (Hawitin and Hebblewaite, 1993). Though different factors may attribute for its yield variation and reduction, the most important reasons could be degradation of biotic resources such as rhizobia and nitrogen deficiency in faba bean growing areas (Graham and Vance, 2000) because symbiotically effective rhizobia increase nodulation, N-fixation, growth and yield of their host (Graham and Vance, 2000; Kiros Habtegebrial and Singh, 2006). Exploiting BNF can be one of the alternatives to enhance soil fertility in Tigray considering the severe land degradation, and unavailability and unaffordability of commercial fertilizers for resource poor farmers This reflects the need to study the effect of indigenous rhizobia on nodulation and growth of faba bean to fully realize the role of BNF. This study was initiated with the aim of studying morphological and physiological characteristics of the indigenous rhizobia, and their effect on nodulation and growth of the crop in the major faba bean producing areas of Tigray
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