Is there a need for Bradyrhizobium yuanmingense and B. japonicum reinoculation in subsequent cropping seasons under smallholder farmers’ conditions? (original) (raw)
Related papers
It was previously demonstrated that there are no indigenous strains of Bradyrhizobium japonicum forming nitrogen-fixing root nodule symbioses with soybean plants in arable field soils in Poland. However, bacteria currently classified within this species are present (together with Bradyrhizobium canariense) as indigenous populations of strains specific for nodulation of legumes in the Genisteae tribe. These rhizobia, infecting legumes such as lupins, are well established in Polish soils. The studies described here were based on soybean nodulation field experiments, established at the Poznan´University of Life Sciences Experiment Station in Gorzyn´, Poland, and initiated in the spring of 1994. Long-term research was then conducted in order to study the relation between B. japonicum USDA 110 and USDA 123, introduced together into the same location, where no soybean rhizobia were earlier detected, and nodulation and competitive success were followed over time. Here we report the extra-long-term sapro-phytic survival of B. japonicum strains nodulating soybeans that were introduced as inoculants 20 years earlier and where soybeans were not grown for the next 17 years. The strains remained viable and symbiotically competent, and molecular and immu-nochemical methods showed that the strains were undistinguishable from the original inoculum strains USDA 110 and USDA 123. We also show that the strains had balanced numbers and their mobility in soil was low. To our knowledge, this is the first report showing the extra-long-term persistence of soybean-nodulating strains introduced into Polish soils and the first analyzing the long-term competitive relations of USDA 110 and USDA 123 after the two strains, neither of which was native, were introduced into the environment almost 2 decades ago.
Persistence of twoRhizobium etli inoculant strains in clay and silty loam soils
Journal of Basic Microbiology, 2005
The persistence of Rhizobium etli strains CE3 and Ph 163 was studied in two soil types representing major French bean growing areas in Egypt. Clay soil from MENOUFIA and silty loam soil from ISMAILIA were planted by bean Cultivars; Bronco and Giza 6. The inoculation with strain Ph 163 in the first bean cultivation was significantly higher in nodule biomass and number; whereas, the strain CE3 was significantly higher in plant biomass accumulation (MOAWAD et al. 2004). The persisting inocula strains seem to perform differently in the two soils in terms of nodulation, biomass accumulation and N-uptake by the two cultivars as compared with their performance with the first inoculation. CE3 strain persisting in the soil performed better than Ph.163 strain. The nodule occupancy by the persisting inoculant rhizobial was determined by two approaches; fluorescent antibody (FA) technique and other Rep-PCR fingerprinting. Both techniques were close in the evaluation of persisting inoculant strains which nodulated beans in the second planting season without inoculation. The results obtained showed that both strains are good survivors in the two soils.
Microbial Ecology, 2007
The plasticity of rhizobial genomes is far greater than previously thought, with complex genomic recombination events that may be accelerated by the often stressful environmental conditions of the tropics. This study aimed at evaluating changes in soybean rhizobia due to adaptation to inhospitable environmental conditions (high temperatures, drought, and acid soils) in the Brazilian Cerrados. Both the host plant and combinations of four strains of soybean Bradyrhizobium were introduced in an uncropped soil devoid of rhizobia capable of nodulating soybean. After the third year, seeds were not reinoculated. Two hundred and sixty-three isolates were obtained from nodules of field-grown soybean after the seventh year, and their morphological, physiological, serological, and symbiotic properties determined, followed by genetic analysis of conserved and symbiotic genes. B. japonicum strain CPAC 15 (same serogroup as USDA 123) was characterized as having high saprophytic capacity and competitiveness and by the seventh year represented up to 70% of the cultivable population, in contrast to the poor survival and competitiveness of B. japonicum strain CPAC 7 (same serogroup as CB 1809). In general, adapted strains had increased mucoidy, and up to 43% of the isolates showed no serological reaction. High variability, presumably resulting from the adaptation to the harsh environmental conditions, was verified in rep-PCR (polymerase chain reaction) profiles, being lower in strain CPAC 15, intermediate in B. elkanii, and higher in CPAC 7. Restriction fragment length polymorphism (RFLP)-PCR types of the 16S rDNA corresponded to the following: one type for B. elkanii species, two for B. japonicum, associated to CPAC 15 and CPAC 7, and unknown combinations of profiles. However, when nodC sequences and RFLP-PCR of the nifH region data were considered, only two clusters were observed having full congruence with B. japonicum and B. elkanii species. Combining the results, variability was such that even within a genetically more stable group (such as that of CPAC 15), only 6.4% of the isolates showed high similarity to the inoculant strain, whereas none was similar to CPAC 7. The genetic variability in our study seems to result from a variety and combination of events including strain dispersion, genomic recombination, and horizontal gene transfer. Furthermore, the genetic variability appears to be mainly associated with adaptation, saprophytic capacity, and competitiveness, and not with symbiotic effectiveness, as the similarity of symbiotic genes was higher than that of conserved regions of the DNA.
Stability of Bradyrhizobium japonicum Inoculants after Introduction into Soil
Applied and Environmental Microbiology
Bradyrhizobium japonicum USDA 125-Sp, USDA 138, and USDA 138-Sm had been used as inoculants for soybean (Glycine max (L.) Merr.) in soils previously free of B. japonicum. At 8 to 13 years after their release, these strains were reisolated from soil samples. A total of 115 isolates were obtained through nodules, and seven colonies were obtained directly by a serological method. The stability of the inoculants was confirmed by comparing the reisolated cultures with their respective parental strains which had been preserved by being lyophilized or stored on a yeast extract-mannitol agar slant at 4°C. Comparisons were made on morphological and serological characters, carbon compound utilization (8 tested), intrinsic antibiotic resistance (9 tested), and enzymatic activity (19 tested). Mucous and nonmucous isolates of serogroup 125 were analyzed for symbiotic effectiveness and restriction fragment hybridization with a DNA probe. Our data suggest that the B. japonicum inoculants have survived for up to 13 years in the soils without significant mutation except for two reisolates with a slightly increased kanamycin resistance level.
Establishment of Bradyrhizobium japonicum and B. elkanii strains in a Brazilian Cerrado oxisol
Biology and Fertility of Soils, 2004
The competition with established soil populations of Bradyrhizobium able to nodulate soybean has been one of the major constraints to the introduction of more efficient strains in Cerrados soils. The effects of nodulation establishment and persistence of four serologically distinct strains of Bradyrhizobium japonicum (CPAC 15 and CPAC 7, belonging to serogroups USDA 123 and CB 1,809) and B. elkanii (29 W and SEMIA 587, belonging to serogroups 29 W and 587) were examined. These strains were introduced in a dark-red oxisol, without indigenous populations of soybean bradyrhizobia, and were evaluated for 6 years. The experimental design was a completely randomized block with four replicates. In the first year, besides the inoculation treatments, there was also an uninoculated control. In the second year, the main plots were split into three sub-plots and treatments consisted of an uninoculated control, CPAC 7 and CPAC 15. In the third year, the entire area was inoculated with CPAC 7. In the fourth and sixth years, the plots were planted with soybean without inoculation, and in the fifth year the plots were left fallow. The strains introduced in the first year influenced nodule occupancy by strain CPAC 7 until the third successive growing season. By the fourth and sixth years, as a consequence of the dispersal of strains serologically related to serocluster 123 in the entire experimental area, this serogroup dominated the nodulation, occurring, on average, in more than 50% of the nodules of the treatments where it had never been inoculated.
Biology and Fertility of Soils, 1989
Sixteen strains ofRhizobium phaseoli were isolated from the Loukkos sandy soil and were compared with four selected strains ofR. phaseoli (CIAT 676, CIAT 57, Olivia, Viking 1) for their N2-fixing ability and for their serological affinities by means of the fluorescent antibody technique. Two indigenous strains were rated as highly effective, six as moderately effective, and eight were ineffective. Viking 1 was ranked as highly effective while the other inoculum strains were moderately effective. None of the 4 inoculum strains cross-reacted with the 16 indigenous strains. The indigenous strains were grouped into only two serogroups but showed a high degree of heterogeneity in regard to the strength of the immunofluorescence response. The inoculum strains outcompeted but did not eliminate the resident population for nodule occupancy on two French bean cultivars (Royalnel and Fetiche). The competitiveness, however, differed between inoculum strains. It was influenced by the host cultivar and by the host cultivar growth stage. Viking 1 was consistent in its high competitive ability whether it was inoculated singly or in a mixture with the other strains. It showed high persistence and formed more than 50% of the nodules 1 year after it was introduced. CIAT 57, Olivia, and CIAT 676 were mediocre in their persistence.