engleski

Genetic diversity and symbiotic efficiency of an indigenous Bradyrhizobium japonicum field population

Composition and characteristics of rhizobial natural field population are of great importance in the soybean production, particularly when introducing commercial inoculant strains under natural conditions. The main aim of the present investigation was to identify and to characterize indigenous soybean rhizobia isolated from different field sites in eastern Croatia. PCR-RFLP of 16S rDNA clearly showed that almost all isolates can be determined as B. japonicum. Fifteen rhizobial strains were characterized and compared with reference and/or type strains representing B. japonicum, B elkanii, B liaoningense and Sinorhizobium fredii. Cluster analysis of combined RFLP patterns obtained with three restriction endonucleases, revealed that fourteen soybean isolates were identical with B. japonicum type and reference strains. Only one isolate (63) was grouped together with S. fredii type strain into second major cluster although they differ at similarity level of 0.62. All isolates were further characterized by RAPD fingerprinting that enabled strain differentiation. Among B. japonicum strains high level of diversity was determined. Dendrogram derived from RAPD profiles showed that all indigenous strains could be divided into three main groups. Most of isolates, including B. japonicum type and reference strains, were grouped within the first major cluster that could be further subdivided into two groups with almost equal strain number. The other major cluster consisted of only two related but not identical B. japonicum isolates (54 and 65). During the two years investigations in field experiments, the symbiotic efficiency of all rhizobial isolates was evaluated. In both years, seed inoculation with particular indigenous strains caused signficant increase of nodule number and nodule dry weight. The best nodulation was achieved by using the same strains (54 and 65) that formed separate group of bradyrhizobia based on their RAPD profiles. Seed inoculation with the isolate that considerably differed from all other strains based on RFLP profiles, resulted in signficantly lowes values for nodule number and dry weight. The application of various indigenous strains caused also significant differences in seed yield. The lowes seed yield was determined on variants inoculated with those two indigenous strains that gave the best nodulation. The application of these two strains also resulted signficantly lower values for seed protein content. Seed yield and seed protein content were also signficantly lower with strain 63 in comparison with the most of other isolates. The resultes from field experiments showed that strains isolated from natural population significantly differ from each other regarding their infectiveness and symbiotic efficiency.

Bradyrhizobium japonicum; genetic diversity; symbiotic efficiency; soybean; PCR-RFLP; seed yield; seed protein content

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