ABSTRACTCowpea is a legume of great agronomic importance that establishes symbiotic relationships with nitrogen-fixing bacteria. However, little is known about the genetic and symbiotic diversity of these bacteria in distinct ecosystems. Our study evaluated the genetic diversity and symbiotic efficiencies of 119 bacterial strains isolated from agriculture soils in the western Amazon using cowpea as a trap plant. These strains were clustered into 11 cultural groups according to growth rate and pH. The 57 nonnodulating strains were predominantly fast growing and acidifying, indicating a high incidence of endophytic strains in the nodules. The other 62 strains, authenticated as nodulating bacteria, exhibited various symbiotic efficiencies, with 68% of strains promoting a significant increase in shoot dry matter of cowpea compared with the control with no inoculation and low levels of mineral nitrogen. Fifty genotypes with 70% similarity and 21 genotypes with 30% similarity were obtained through repetitive DNA sequence (BOX element)-based PCR (BOX-PCR) clustering. The 16S rRNA gene sequencing of strains representative of BOX-PCR clusters showed a predominance of bacteria from the genusBradyrhizobiumbut with high species diversity.Rhizobium,Burkholderia, andAchromobacterspecies were also identified. These results support observations of cowpea promiscuity and demonstrate the high symbiotic and genetic diversity of rhizobia species in areas under cultivation in the western Amazon.

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Figurando como um dos principais produtores e exportadores de soja o Brasil destaca-se pela potencialidade de plantio de duas safras, uma em seguida da outra, também conhecidas como safra principal e safrinha. Para realização da safrinha com o milho, por exemplo, é necessário à utilização de cultivares precoces de soja que antecipem o período de plantio na segunda safra. Sendo assim, objetivou-se com este trabalho estudar a adaptabilidade de cultivares precoce de soja para o cultivo de verão na Região Sul de Minas Gerais. Os caracteres avaliados foram produtividade de grãos, altura de plantas, inserção do primeiro legume e ciclo de cultivo das cultivares introduzidas. O experimento foi conduzido na safra 2012/2013 e 2013/2014, adotando o delineamento experimental de blocos casualizados, com 25 cultivares e três repetições. Os resultados obtidos foram submetidos à análise de variância conjunta e as médias comparadas pelo teste de Scott-Knott (1974) a 5 % de probabilidade, com o auxílio do pacote estatístico SISVAR. Adotou-se a estimativa da acurácia para precisão experimental. Em função dos resultados obtidos pode-se inferir que das cultivares avaliadas destaca-se a cultivar BMX Força RR, por apresentar características favoráveis ao cultivo de verão, possibilitando a realização de segunda safra na região sul de Minas Gerais, associado a boas características agronômicas e precocidade.

SUMMARYThe genetic diversity of ten Bradyrhizobium strains was evaluated for tolerance to high temperatures, to different salinity levels and for the efficiency of symbiosis with cowpea plants (Vigna unguiculata (L.) Walp.). Eight of these strains were isolated from nodules that appeared on cowpea after inoculation with suspensions of soil sampled from around the root system of Sesbania virgata (wand riverhemp) in ecosystems of South Minas Gerais. The other two strains used in our analyses as references, were from the Amazon and are currently recommended as cowpea inoculants. Genetic diversity was analyzed by amplifying repetitive DNA elements with the BOX primer, revealing high genetic diversity with each strain presenting a unique band profile. Leonard jar assays showed that the strains UFLA 03-30 and UFLA 03-38 had the highest N 2 -fixing potentials in symbiosis with cowpea. These strains had more shoot and nodule dry matter, more shoot N accumulation, and a higher relative efficiency than the strains recommended as inoculants. All strains grew in media of pH levels ranging from 4.0 to 9.0. The strains with the highest N 2 -fixing efficiencies in symbiosis with cowpea were also tolerant to the greatest number of antibiotics. However, these strains also had the lowest tolerance to high salt concentrations. All strains, with the exceptions of UFLA 03-84 and UFLA 03-37, tolerated temperatures of up to 40 ºC. The genetic and phenotypic characteristics of the eight strains isolated from soils of the same region were highly variable, as well as their symbiotic efficiencies, despite their

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