Genetic diversity of rhizobia associated with alfalfa in Serbian soils

We have evaluated the genetic diversity and phylogeny of alfalfa rhizobia, originating from different types of soils in Serbia and their ability to establish an effective symbiosis with alfalfa (Medicago sativa L.). A collection of 65 strains isolated from root nodules of alfalfa were characterized by rep-PCR analysis, partial and complete 16S rDNA gene and recA gene sequencing, as well as atpD gene sequencing and DNA-DNA hybridizations. The results of the sequence analyses revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules. Only one strain was identified as Sinorhizobium medicae, two strains as Rhizobium tibeticum and one strain as Rhizobium sp. Despite the fact that the majority of strains were identified as S. meliloti, a high genetic diversity at strain level was detected. Almost all isolates shared the ability to nodulate and fix nitrogen with M. sativa, except 11 of them, which were incapable of fixing nitrogen with this species. About 50% of the isolates showed values of symbiotic effectiveness (SE) above 50%, while 10% of the strains were highly effective with SE values above 70%. Some of the strains which were highly effective in nitrogen fixation at the same time could intensively solubilize phosphates, offering a possibility for multipurpose inoculum development. This was the first genetic study of rhizobia isolated from this region and also the first report of natural presence of R. tibeticum in root nodules of M. sativa

EFFECTS OF DIFFERENT STRAINS OF Sinorhizobium meliloti ON ALFALFA

**Original scientific paper Abstract: The effects of highly effective strains of Sinorhizobium meliloti on biomass and crude protein yields of alfalfa (Medicago sativa L.) were investigated in a three-year field experiment focusing on the advantage of alfalfa inoculation with N microbiological fertilizer over N mineral fertilization on chernozem soil. Strains 236 and 234 were found in this experiment to have significant effect on the yields of dry matter and proteins, by comparison to untreated control plants. In the third year of utilization, dry matter yield of alfalfa plants inoculated with strains 236 and 234 increased around 31 % in the first cutting and 53 % and 65 % in the second one, compared to control plants. Strain 236 was found to increase the yield of crude proteins by 29.7 % (second cutting) and 39.6 % (third cutting) in the second year, and 27.5 % (first cutting) and 50.3 % (second cutting) in the third year of utilization, while strain 234 increased significantly the content of proteins in the third cutting of the second year (27%) and in the third year of utilization (51 % in the first and 53 % in the second cutting). The results indicate that effective strains of S. meliloti may be applied as N microbiological fertilizers on soils with optimal physical and chemical characteristics and autochthonous populations that may not have satisfactory effectiveness in nitrogen fixation

Native Mesorhizobium strains improve yield and nutrient composition of the common bird's-foot trefoil grown in an acid soil

10 Pág.Acid soils occupy more than 3.95 billion ha of the world soils, and finding an adequate solution for the limitation of crop production on these soils is indispensable. Using highly effective rhizobia tolerant to low pH enables successful nodulation and quality crop production of legumes in acid soils. In this study, isolation and characterization of native rhizobia associated with root nodules of bird's-foot trefoil (Lotus corniculatus L.) from Serbia were conducted. Their effects on the plant yield and nutrient composition of bird's-foot trefoil grown in an acid soil (pH 5.4), in a pot experiment were evaluated. Out of 72 strains isolated, 40 could nodulate bird's-foot trefoil when reinoculated in the test tubes under gnotobiotic conditions, and 23 isolates showed high nitrogen-fixing efficiency. Overall, all isolates could grow well in medium with a pH between 4.5 and 8. Indole-3-acetic acid (IAA) production was detected in all nodulating isolates and 24 could solubilize inorganic phosphates. The identification of selected isolates showed that all belong to Mesorhizobium genus (M. tianshanense, M. erdmanii, M. cantuariense, M. loti, M. jarvisii and M. caraganae). Four acid-tolerant isolates (1M12, 631oz, U1C, and 754) with high nitrogen-fixing efficiency in vitro and particular PGP traits were selected for the pot experiment with acid soil. All applied bacterial treatments (except 1M12) increased the shoot dry weight of bird's-foot trefoil plants (up to 50%), compared to the control. In addition, N uptake and N% were increased up to 20% by inoculation. All applied treatments influenced the concentrations and improved uptake of macro (P, K, Ca, and Mg) and micronutrients (Cu, Fe, Mn, Ni, Zn, and B) in the plant material. The obtained results indicated that satisfactory yield and mineral composition of L. corniculatus in acid soils could be achieved by inoculation with selected Mesorhizobium strains.This research was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, under the contract numbers 451-03-9/2021-14/200011 and 451-03-9/2021-14/200178.Peer reviewe

Biostimulant effects of rhizobacteria on wheat growth and nutrient uptake depend on nitrogen application and plant development

The capacity of plant growth-promoting rhizobacteria (PGPR) - Bacillus amyloliquefaciens GB03 (BamGB03), B. megaterium SNji (BmeSNji), and Azospirillum brasilense 65B (Abr65B) – to enhance growth and nutrient uptake in wheat was evaluated under different mineral N fertilizer rates, in sterile vs. non-sterile soils, and at different developmental stages. In gnotobiotic conditions, the three strains significantly increased plant biomass irrespective of the N rates. Under greenhouse conditions using non-sterile soil, growth promotion was generally highest at moderate N rate, followed by full N dose, while no significant effect of the inoculants was observed in the absence of N fertilizer. At 50N, plant biomass was most significantly increased in roots (up to +45% with Abr65B) at stem-elongation stage and in the ears (+19–23% according to the strains) at flowering stages. For some nutrients (N, P, Mn, and Cu), the biomass increases in roots and ears was paralleled with lowered nutrient concentrations in the same organs. Nevertheless, growth stimulation resulted in higher total nutrient uptake and nutrient uptake efficiency. Furthermore, Abr65B and BmeSNji counteracted the repression of root development caused by high N supply. Therefore, combining PGPR with a proper cultivated system, N rate, and plant stage could enhance their biostimulant effects