Evaluating the biological nitrogen fixation of rhizobial strains with two cultivars of bean using 15N isotope dilution techniques
2006
Asadi Rahmani, Hadi | Pirvavi, Nejat | Khavazi, Kazem | Hemati, Vida | Saqafi, Kobra | Khorasani, A`li | Teymuri, Sa`d Ol-Lah | Saqeb, Nasr Ol-Lah
Legume crops have been approved to have significant effects on soil fertility and nitrogen management from many years ago. These plants can fix atmospheric nitrogen in symbiosis with soil bacteria named rhizobium. In many cases the crops are planted in rotation with legumes will profited by this phenomenon. Common bean is an important source of protein and calorie and can fix more than 100 kg of N/ha, which meets about 70% of plant N requirements. Different methods have been used for measurement of N fixed. Acetylene reduction assay has not enough accuracy and will only useful for screening of high numbers of rhizobium strains or plant cultivars. Ureides assay in legume xylem sap is expensive and time consuming and so is not used extensively. Methods such as measurement of plant N content and N-difference are currently used for strain or cultivar selection in Iran as well as many countries in the world. Non of the above methods could not be used for accurate measurement of N fixed. Tracer methods by using nitrogen isotopes could be very useful for evaluation of biological nitrogen fixation. Isotope dilution method which is based on using the 15N enriched materials and assessment of 14N/15N ratio in legume plants, is used increasingly since thirty years ago. In this study isotope dilution method was employed to assess the nitrogen fixation potential of four rhizobial strains in symbiosis with two cultivars of common bean. All of the strains were able to fix more than 100kg of N/ha, although there were no significant differences between the strains as well as between the plant cultivars. Indigenous strains fixed more nitrogen compared to the two others. Seed yield production in Naz cultivar was higher than Talash.
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