Forage legumes are important resources in semiarid regions due to their abilities to adapt to soils with low fertility and fix nitrogen when associated with diazotrophic bacteria. Here, we applied a polyphasic approach to characterize a set of legume nodule isolates obtained from Clitoria ternatea and Stylosanthes capitata cultivated in the soils of a semiarid region of Brazil. A total of 126 bacterial isolates were obtained: 45 isolates from C. ternatea and 81 isolates from S. capitata. Nodulation tests revealed only ten isolates that nodulated their original host: six isolates from C. ternatea and four isolates from S. capitate. These ten legume nodule isolates were phenotypically and genotypically characterized. All isolates grew in fructose, glucose, sodium glutamate, maltose, xylose, and sucrose. Metabolic tests showed a relationship between tolerance to salt and high temperatures, where isolates that tolerated the highest salt concentration also tolerated the highest temperature. Three isolates showed amylolytic activity, and four isolates showed carboxymethyl cellulolytic activity. Streptomycin was the most limiting and nalidixic acid was the least limiting antibiotic to bacterial growth. Seven out of ten isolates were indol-acetic acid producers. Additionally, 16S rRNA gene partial sequencing enabled the identification of members of the genera Bacillus (1), Bradyrhizobium (4), Leifsonia (3), Microvirga (1), and Rhizobium (1). These data reveal phenotypically and genotypically diverse bacteria inhabiting the nodules of the forage legumes C. ternatea and S. capitata represent an important microbial source to protect new biotechnological products and improve forage legumes in semiarid regions.

In this study, the effect of microbial inoculants and fertilizer application on cowpea (BRS Pujante) growth and on the structure and composition of arbuscular mycorrhizal fungi (AMF) assemblages were evaluated. A completely randomized experiment was set up involving 17 treatments: four with AMF, three with nodulating bacteria, six with AMF + nodulating bacteria, two with phosphorus, one with nitrogen and one control (reference) in five replicates. Plant growth and nutritional content, mycorrhizal colonization, glomerospores number, spore-based AMF assemblages and ecological indices were evaluated. Mycorrhizal inoculants associated with Bradyrhizobium BR3267 strain were more effective than the Microvirga BR3296 strain. Multidimensional scaling analysis showed that Acaulospora longula treatments were more similar among themselves, and distinct from the other treatments. A difference was observed in the structure of AMF community assemblage between treatments with G. albida + Bradyrhizobium BR 3267 and A. longula, with greater Shannon diversity and Pielou equitability indices in the first treatment and greater dominance in the treatment with A. longula only. Long-term studies are required to determine if the successful establishment of A. longula among indigenous species persists over time and if its dominant behavior is not deleterious to the AMF native community.

Water scarcity is a major challenge in northeastern Brazil, where efficient water management strategies are essential for sustainable agriculture. This study aimed to evaluate the performance of melon hybrids in terms of biomass production and nutritional status under varying irrigation levels and mycorrhizal fungi (AMF) inoculation. The experiment was conducted in a greenhouse at the State University of Bahia (Juazeiro, BA, Brazil) using a randomized block design with a 4 × 2 × 4 sub-subdivided plot scheme. The treatments included four irrigation levels (50%, 75%, 100%, and 125% of crop evapotranspiration—ETc), two melon hybrids (Juazeiro and Mandacaru), and four AMF inoculation treatments (non-inoculated with AMF, Entrophospora etunicata, Acaulospora longula, and their combination), with 10 replications. The results indicated that the inoculation with A. longula significantly improved biomass production and plant nutrition, particularly for the Juazeiro hybrid. The most significant improvements were observed in biomass production and nutritional status when this mycobiont was used, highlighting the potential of AMF inoculation as a strategy to enhance water use efficiency and plant tolerance under water-limited conditions. Root colonization in melon plants ranged from 6% to 60%, with an overall average of 36.2%, in Experiment I, and from 6% to 72%, with an average of 40%, in Experiment II. Melon biomass production responded differently to irrigation levels, with Experiment I showing polynomial decreases in biomass as water levels decreased, while Experiment II exhibited linear increases in biomass with higher irrigation, likely influenced by supplementary fertilization. When evaluated, the levels of macronutrients present in the aerial part of the plants did not show significant differences for the treatments concerning the levels of P, K, and Mg, except for Ca. These findings suggest that A. longula is a suitable mycobiont for optimizing melon plant performance in regions with limited water resources, like northeastern Brazil. The study also emphasizes the importance of selecting appropriate Mycorrhizal fungi to maximize symbiotic benefits in melon cultivation under deficit irrigation systems.

Este livro é o resultado do trabalho de parceria do professor Jairton Fraga Araújo com a professora Lúcia Marisy e com a colaboração e o esforço de diversos outros professores e alunos do Programa de Pós-Graduação em Agroecologia e Desenvolvimento Territorial (PPGADT), em nível Doutorado Profissional, fundado a partir de uma associação de Universidades da Região Nordeste do Brasil, formada pela Universidade Federal do Vale do São Francisco (UNIVASF), Universidade Federal Rural de Pernambuco (UFRPE) e Universidade do Estado da Bahia (UNEB). Inicialmente, imponho-me o dever de apresentar as ideias e os resultados que colhemos na semeadura desta parceria, para então colocar ao leitor as questões mais difíceis a que os trabalhos aqui reunidos impelem a pensar, pesar e ocupar, mediante o esforço da leitura, da crítica e da reflexão.

The pigeonpea (Cajanus cajan) crop has a high potential for sustainable agricultural systems in semiarid regions due to its robustness, multifunctionality, and ability to perform biological nitrogen fixation in symbiosis with rhizobia. This study aimed to isolate and characterize native rhizobia at the molecular and symbiotic levels from pigeonpea root nodules cultivated in soils of the Brazilian drylands. A total of 19 bacterial isolates were obtained, 12 of which amplified the symbiotic nifH and nodC genes, which were subjected to Box-PCR fingerprinting and 16S rRNA gene sequencing. The isolates were classified into the Bradyrhizobium, Rhizobium, and Agrobacterium genera, with a notable genetic diversity observed even among samples from the same region. In a completely randomized greenhouse experiment under gnotobiotic conditions, 11 out of the 12 isolates exhibited symbiotic efficiency comparable to that of the commercial strain Bradyrhizobium pachyrhizi BR 2003 in at least one of the evaluated parameters (shoot dry biomass, number of nodules per plant, and N accumulation). The results indicate the presence of promising native rhizobia for use in inoculants adapted to the conditions of the Brazilian semiarid region, particularly the strains ESA 769, ESA 770, ESA 775, ESA 776, and ESA 777. Additionally, the presence of Agrobacterium strains capable of forming functional nodules in pigeonpea suggests the occurrence of horizontal gene transfer of symbiotic genes.