Genomic identification and characterization of the elite strains Bradyrhizobium yuanmingense BR 3267 and Bradyrhizobium pachyrhizi BR 3262 recommended for cowpea inoculation in Brazil

ABSTRACT The leguminous inoculation with nodule-inducing bacteria that perform biological nitrogen fixation is a good example of an "eco-friendly agricultural practice". Bradyrhizobium strains BR 3267 and BR 3262 are recommended for cowpea (Vigna unguiculata) inoculation in Brazil and showed remarkable responses; nevertheless neither strain was characterized at species level, which is our goal in the present work using a polyphasic approach. The strains presented the typical phenotype of Bradyrhizobium with a slow growth and a white colony on yeast extract-mannitol medium. Strain BR 3267 was more versatile in its use of carbon sources compared to BR 3262. The fatty acid composition of BR 3267 was similar to the type strain of Bradyrhizobium yuanmingense; while BR 3262 was similar to Bradyrhizobium elkanii and Bradyrhizobium pachyrhizi. Phylogenetic analyses based on 16S rRNA and three housekeeping genes placed both strains within the genus Bradyrhizobium: strain BR 3267 was closest to B. yuanmingense and BR 3262 to B. pachyrhizi. Genome average nucleotide identity and DNA-DNA reassociation confirmed the genomic identification of B. yuanmingense BR 3267 and B. pachyrhizi BR 3262. The nodC and nifH gene analyses showed that strains BR 3267 and BR 3262 hold divergent symbiotic genes. In summary, the results indicate that cowpea can establish effective symbiosis with divergent bradyrhizobia isolated from Brazilian soils.

Óleo essencial de Baccharis trimera (Less. ) DC. sobre o potencial fisiológico de sementes de feijão caupi / The essential oil effects of Baccharis trimera (Less. ) DC. on the physiological potential of cowpea bean seeds

O presente trabalho teve como objetivo avaliar o efeito alelopático do óleo essencial de plantas de carqueja, Baccharis trimera (Less.) DC., sobre a germinação de sementes de feijão Vigna unguiculata (L.) Walp. Foi avaliado o efeito do óleo essencial de B. trimera sobre V. unguiculata nas dosagens 20 μL, 15 μL, 10 μL, 5 μL e testemunha. A qualidade fisiológica das sementes foi determinada pela porcentagem de emergência, velocidade de emergência e índice de velocidade de emergência. O delineamento experimental foi o inteiramente casualizado, em esquema fatorial 5 x 2 com cinco repetições. Não foi observado efeito inibidor do óleo essencial de B. trimera na germinação de sementes de feijão caupi, caracterizando-se como de efeito alelopático benéfico. De acordo com os resultados obtidos, o óleo essencial de B. trimera revelou-se eficiente na manutenção da viabilidade dessas sementes.

This research aimed to evaluate the allellopathic effect of essential oils of the Baccharis trimera (Less.) DC. plants on the seeds germination of cowpea Vigna unguiculata (L.) Walp. The effect of B. trimera essential oil on V. unguiculata was evaluated at levels of 20 μL, 15 μL, 10 μL, 5 μL and control. The physiologic quality of the seeds was determined by percentage emergence, the rate of speed emergence and speed emergence index. The data analysis was carried out using an entirely randomized design, in a 5 x 2 factorial scheme with five repetitions. An inhibitory effect of B. trimera essential oil on bean seeds germination was not observed, which is characterized as a beneficial allelopathic effect. Based on the results, the B. trimera essential oil proved efficient in the viability maintenance of these seeds.

Resposta do feijão-caupi à doses e formas de aplicação de fósforo em Latossolo Amarelo do Estado de Roraima / Response of cowpea (Vigna unguiculata (L. ) Walp. ) to phosphorus fertilization levels and application forms in Yellow Latosol of Roraima State/Brazil

A adubação fosfatada e as formas de aplicação de fertilizantes fosfatados são fatores importantes no manejo das culturas. O objetivo do presente trabalho foi avaliar os efeitos de doses de fósforo e formas de aplicação de fertilizante fosfatado na cultura do feijão-caupi (Vigna unguiculata (L.) Walp) em solo de cerrado do Estado de Roraima. O experimento foi realizado em condições de campo, em Latossolo Amarelo distrocoeso, no Campus do Cauamé da Universidade Federal de Roraima. O delineamento experimental foi o de parcelas subdivididas, com as parcelas principais organizadas em blocos casualizados, com três repetições. As parcelas foram constituídas pelas formas de aplicação do fertilizante fosfatado: a) Lanço - L; b) Sulco simples - SS e c) Sulco duplo - SD. As subparcelas corresponderam às doses da adubação fosfatada: 0; 0,5; 1,0; 1,5 e 2,0 vezes a dose recomendada para adubação de manutenção do feijão-caupi. Houve efeito das doses de fósforo sobre o crescimento e absorção de fósforo pelas plantas. O maior crescimento, produção de vagem por planta, de grãos e absorção de fósforo ocorreu com a aplicação do fertilizante fosfatado aplicado em sulcos duplos.

Phosphorus fertilization and ways of phosphate fertilizers application are important factors considering crop management. This study aimed at assessing the effect of phosphorus rates and phosphate fertilizers application forms on growth and phosphorus uptake of cowpea plants cropped on cerrado soil in the State of Roraima, Brazil. An experiment took place under field conditions, on a Yellow Latosol, at Cauamé Campus of Roraima's Federal University, located in the municipality of Boa Vista/RR. The experimental design was split-plot, in a completely randomized blocks, with three replicates. The plots consisted of the following phosphoric fertilizers application forms: a) broadcasting; b) single furrow and c) double furrow. Sub-plots corresponded to phosphorus doses: 0, 0,5; 1,0; 1,5, and 2,0 times the recommended dose for cowpea maintenance fertilization (60 kg ha-1 of P2O5). There was a significant effect of P rates over plant growth and plant uptake. Application of fertilizer in double furrows promoted higher plant growth, grain yield, and plant phosphorous uptake.