Plant breeding programs seek to obtain genotypes with high yield, yield stability, and wide adaptability to environments. Selection of strains (genotypes) for adoption as crop inoculants has a similar aim. However, in both cases, the genotype × environment interaction hinders selection of materials adapted to the most diverse edaphic and climatic conditions. Nevertheless, with adequate biometric techniques, the variation in the response of each strain in the environments can be analyzed, allowing selection of those with the type of response and standard desired. In the present pioneering field study, the Toler and additive main effects and multiplicative interaction analysis models and the Annicchiarico method were used in a complementary manner with strains of nitrogen‐fixing bacteria that are symbionts with cowpea to determine their adaptabilities and phenotypic stabilities. The adaptability and phenotypic stabilities of strains INPA 03‐11B and UFLA 03‐164 were confirmed by these techniques. These strains have the most stable behavior regardless of the environment. The reliability of adopting these strains exceeded 85%. The good response of strain UFLA03‐164, still in the selection phase, is surprising, with results equivalent to application of mineral N, allowing it to be included among the strains approved as inoculants for cowpea.

Core Ideas Captan and difenoconazole compromise in vitro survival of Rhizobium tropici CIAT 899. In the field, native rhizobia were clearly tolerant to most of the fungicides evaluated. Among the fungicide treatments assessed in the field, only difenoconazole is potentially damaging. When difenoconazole treatment is indispensable, in‐furrow inoculation may be the most alternative. Due to the effects observed in vitro, similar precautions should also be taken with captan in the field. Though some studies observed negative effects of fungicide seed treatment on yield of common bean (Phaseolus vulgaris L.), few studies have directly evaluated fungicide compatibility with seed inoculation treatments in field conditions. For fungicides that are incompatible, rhizobia inoculation in the planting furrow (in‐furrow inoculation) would permit combined use of both management practices since this would avoid direct contact between the chemical compound and the rhizobia. Thus, the aim of this study was to evaluate the compatibility of seed fungicide treatment and rhizobia inoculation techniques to improve N derived from rhizobia symbiosis in common bean. A preliminary in vitro experiment evaluated the survival of Rhizobium tropici after contact with fungicides compared with an untreated control. Two field experiments were conducted in a 6 × 4 factorial arrangement involving the same treatments used for the in vitro survival test, as well as four sources of N [two types of liquid inoculation (inoculation on the seed or in‐furrow inoculation), plus two controls without inoculation]. We concluded that captan and difenoconazole fungicides reduced in vitro survival of rhizobia inoculated on the seed. Yield measurements in the field studies indicated that symbiotic nitrogen fixation could replace N fertilization, regardless of the inoculation treatment method and environmental conditions. Difenoconazole is potentially harmful to native bacteria in the field; therefore, in‐furrow inoculation may be recommended when the use of difenoconazole is necessary. Moreover, based on the harmful effects observed in vitro, precautions similar to the use of difenoconazole should also be taken when using captan fungicide in field conditions.

Sophora tomentosa is a pantropical legume species with potential for recovery of areas degraded by salinization, and for stabilization of sand dunes. However, few studies on this species have been carried out, and none regarding its symbiotic relationship with beneficial soil microorganisms. Therefore, this study aimed to evaluate the diversity of nitrogen-fixing bacteria isolated from nodules of Sophora tomentosa, and to analyze the occurrence of colonization of arbuscular mycorrhizal fungi on the roots of this legume in seafront soil. Thus, seeds, root nodules, and soil from the rhizosphere of Sophora tomentosa were collected. From the soil samples, trap cultures with this species were established to extract spores and to evaluate arbuscular mycorhizal fungi colonization in legume roots, as well as to capture rhizobia. Rhizobia strains were isolated from nodules collected in the field or from the trap cultures. Representative isolates of the groups obtained in the similarity dendrogram, based on phenotypic characteristics, had their 16S rRNA genes sequenced. The legume species showed nodules with indeterminate growth, and reddish color, distributed throughout the root. Fifty-one strains of these nodules were isolated, of which 21 were classified in the genus Bacillus, Brevibacillus, Paenibacillus, Rhizobium and especially Sinorhizobium. Strains closely related to Sinorhizobium adhaerens were the predominant bacteria in nodules. The other genera found, with the exception of Rhizobium, are probably endophytic bacteria in the nodules. Arbuscular mycorrhizal fungi was observed colonizing the roots, but arbuscular mycorhizal fungi spores were not found in the trap cultures. Therefore Sophora tomentosa is associated with both arbuscular mycorhizal fungi and nodulating nitrogen-fixing bacteria.

Common bean (Phaseolus vulgaris L.) producers that have adopted a high level of technology have shown interest in the use of liquid inoculant in the planting furrow, especially because of the practicality of this operation in large‐scale planting operations. However, consistent information on this practice is lacking for common bean, which requires studies to assist the producer in the choice of the inoculation method to be adopted and in determination of the application rates adequate for good performance of biological N2 fixation. To that end, two field experiments were conducted under the no‐till system under different soil and climatic conditions, both of them in irrigated areas. A randomized block experimental design was used, with four replications and seven treatments (three rates of liquid inoculation in the planting furrow; peat‐based or liquid inoculation on the seed; and two control treatments without inoculation, without and with N‐urea). The cultivar used was BRSMG Madrepérola and the rhizobial strain was CIAT 899 (±109 cells of Rhizobium tropici per milliliter or gram). Inoculation on the seed was performed shortly before sowing. Inoculation in the planting furrow at the rate of 3.5 L ha−1 not only leads to higher yields than inoculations on the seed but also ensures bean seed yields equivalent to those of the treatment with mineral N. Therefore, due to operational practicality, inoculation in the planting furrow is the most advantageous of the inoculations tested, regardless of the soil and climatic conditions in this study.

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The BRSMG Uai common bean cultivar (Phaseolus vulgaris L.) unites traits required by producers, such as high yield and upright stands, the latter of which is considerably improved in relation to previously released cultivars such as BRSMG Madrepérola and Pérola. However, the potential of the cultivar to form symbiotic relationships with rhizobia to fix N2 has not yet been assessed. Here, field experiments were conducted to assess the efficiency of biological nitrogen fixation (BNF) in the cultivar, and to compare this to the efficiencies of other genetic materials widely grown throughout Brazil (BRSMG Madrepérola and Pérola). Experiments were conducted on two Oxisols in Minas Gerais State, Brazil (one during the dry season in the south, and the other during the winter season in the Alto-Paranaíba region), under a no-tillage system over maize stover. A randomized block experimental design was implemented in a 3 × 3 factorial arrangement with four replicates. Individual and combined Analysis of Variance were performed and the data were normalized. Homogeneity of the residual mean squares was observed. Significant effects of factors were identified by Scott-Knott tests and F tests. The BRSMG Uai cultivar responded to inoculation with the rhizobial strain CIAT 899, with yields similar to those achieved upon fertilization with 80 kg ha-1 of N-urea and to the yields of the BRSMG Madrepérola and Pérola cultivars inoculated with the same rhizobial strain. In terms of commercial use, this cultivar may be successful under either of the management practices adopted for N supply, and from the perspective of plant breeding, it has potential for inclusion in breeding programs directed toward improving BNF.

In spite of the chemical, physical, and biological benefits that Crotalaria spectabilis can provide to the soil, it is little used as a green manure crop by farmers. Inoculation with strains of legume-nodulating nitrogen-fixing bacteria that are efficient and competitive may be a strategy to enhance accumulation of N in C. spectabilis and stimulate adoption of this green manure crop. The aims of this study were i) to evaluate the symbiotic and agronomic efficiency of new strains of Bradyrhizobium on C. spectabilis in an oxisol (red latosol) compared to that of noninoculated controls (without and with mineral N) and with the approved strain BR2811, seeking to corroborate possible recommendation as inoculants for this species; and ii) to determine, the contribution of these treatments to N accumulation in the plant of C. spectabilis in four periods of cutting for determining possible and ideal periods for its incorporation in the soil. Experiments were carried out in pots and field. Inoculation with the new strains UFLA05-03, UFLA05-09, and UFLA05-14 and with BR2811 on C. spectabilis is effective since it increases the production of N-enriched plant biomass when compared to the control without N mineral. However, UFLA05-03 stands out among these strains because it behaves similarly to the control with mineral N both in relation to shoot N accumulation and dry matter just after 150 days in the field.