New Rhizobium leguminosarum bv. trifolii isolates: Evaluation of competitiveness for clover nodule occupancy

Abstract

An interrelationship between introduced and indigenous rhizobia focused on their competitiveness in nodulation was evaluated in a soil pot experiment. Clover seeds were inoculated by six different gradual concentrations of inoculum of two effective Rhizobium leguminosarum bv. trifolii isolates (inoculation strains 1/2 and 14/2). At the beginning of flowering, clover plants were removed from the pots, and nodules from each pot representing different degrees of inoculum level were taken for reisolate cultivation. The PCR technique was used for the identification of rhizobial reisolates, random amplified polymorphic DNA product patterns were acquired and analysed. Nodule occupation by inoculation strains or indigenous Rhizobium leguminosarum bv. trifolii strains was assessed by comparing the number of nodules formed by inoculation or indigenous strains and inoculation strains competitiveness was calculated. Nodule occupancy by the inoculation strain 1/2 increased sharply with the increase in inoculum dose, whereas in inoculation strain 14/2 more nodules were formed gradually starting from low inoculum level. Competitiveness of inoculation strain 1/2 was calculated as low and was documented by an absence of nodule occupancy in four inoculation levels. On the other hand, competitiveness of the inoculation strain 14/2 was considerably higher, and even in low inoculum dose this strain was more competitive than native rhizobia. Although both the inoculation strains 1/2 and 14/2 were found highly efficient in nitrogen fixation, only the strain 14/2 was able to manifest this characteristic due to the higher competitiveness when applied in lower doses.

Nodule occupancy byRhizobium leguminosarumstrain WSM1325 following inoculation of four annualTrifoliumspecies in Canterbury, New Zealand

“…DNA fingerprinting of these strains demonstrated a high genotypic diversity with between 26 and 35 different strains present within 55Á58 nodules recovered from each of the four clover species. This is the first New Zealand study to demonstrate a large number of genotypes present in a single field using ERIC-PCR, however, similar results have been shown for surveys of naturalized rhizobia in Australian pastures (Ballard et al 2002;Denton et al 2002;Simon & Salava 2006). This work reinforces other work (using chromosomal and plasmid restriction fragment length polymorphism) done at the University of Otago, New Zealand, (Elliot 1997;Shah 2003) that demonstrated genotypic variation in rhizobia in New Zealand pastures.…”

Competitiveness of Bradyrhizobium japonicum inoculation strain for soybean nodule occupancy

“…In this study, inoculation strain showed 45% of nodule occupancy in soil 1, and 18% of nodule occupancy in soil 2 (Figure 2). Similarly, Šimon and Salava (2006) reported 0% and 60% of nodule occupancy for two inoculation strains at same inoculation level. Both molecular methods resulted in almost identical grouping of the Bradyrhizobium isolates.…”