Diversidade de rizóbios capazes de nodular leguminosas tropicais

Abstract

Diversidade de rizóbios capazes de nodular leguminosas tropicais 1 RESUMOEm geral, leguminosas tropicais são capazes de formar nódulos com uma ampla faixa de rizóbios, o que contribui significativamente para o aumento da atividade da fixação biológica de nitrogênio. Objetivou-se no presente trabalho, estudar a faixa hospedeira do grupo conhecido genericamente como Rhizobium, rizóbio tropical ou grupo miscelânea caupi, como estratégia para a obtenção de um inoculante eficiente para a cultura do amendoim. ABSTRACTTropical legume species are generally capable of forming nodules with a broad rhizobium range, which contributes significantly to biological nitrogen fixation activity. This work had the objective of studying the host range of Rhizobium group generally referred as tropical rhizobia or miscellanea cowpea group and design strategies for obtaining an efficient inoculant for peanut. Seven species within the Aeschynomeneae tribe were used as host plant for rhizobia present in soil samples from Pernambuco State located in the North-east region of Brazil. Rhizobia were isolated from nodules of Arachis hipoaea, A. villosulicarpa, Stylosanthes guyanensis, S. scabra, Aeschynomene americana, A. paniculata and A. histrix and characterized regarding growth ratio, pH change of culture medium and colony morphology parameters: size, appearance, color, elevation, transparency, form and mucous type and quantity. The fenotipical characterization resulted in the identification of 44 groups. These data were used for estimating diversity indices related to the Rhizobium population present in soil samples under different vegetation and/or management. Shanon and Weaver diversity index and Margalef index indicated that soil covered by native vegetation (caatinga) showed a more diverse rhizobia population than the soil under peanut cultivation.

Biodiversity of rhizobia associated with cowpea cultivars in soils of the lower half of the São Francisco River Valley

“…The dominance indexes were highest in the areas A4 and A1. Santos et al (2007) agrees with the idea that the semi-arid region of Northeastern Brazil (Sertão), including the lower half of the São Francisco river valley, has peculiar features, where the entire biodiversity is under constant stress conditions, of either high temperature or low rainfall levels. These conditions, according to these authors, can affect rhizobium survival and effectiveness in this region and it is possible that the high diversity observed is an indication that the system is able to maintain the functional group even under stress conditions.…”

“…Martins (1996) reported this feature in 25 % of the isolates from soil samples from Petrolina, from the Sertão (semi-arid region) in the State of Pernambuco, using cowpea as trap plant. This frequency was considered high for the crop, which is usually associated with isolates with typical characteristics of strains from the genus Bradyrhizobium (Martins et al, 1997;Melloni et al, 2006), which in turn comprises, generally, slow-growth strains with ability to alkalinize the culture medium (Santos et al, 2007). The evolution of the incidence of rapid-growth isolates over approximately 15 years, from 25 to 62 %, associated with this culture in soils of the lower half of the São Francisco river valley, may be related to climate changes.…”

“…Analyzing a series of climatic data collected at the agrometeorological station of "Embrapa Semi-Arido" in Petrolina-PE, Angelotti (2008) observed positive changes due to the temperature of this region. According to Sprent (1994), rapid-growth rhizobium are common in arid and semiarid regions, and this feature is a survival strategy, since they are more tolerant to drought than those of slow growth, multiplying rapidly in a short period of time (Santos et al, 2007). Regarding the formation of acid and alkali, 63 % acidified the culture medium, 12 % alkalinized it and 25 % maintained the medium pH neutral.…”

Agronomic efficiency of Bradyrhizobium in peanut under different environments in Brazilian Northeast

“…In agriculture, this relationship could be exploited by production and use of inoculants containing efficient strains of rhizobia, and applied directly in seeds or soil (Nogueira and Hungria, 2013). Peanut is a legume able to nodulate with a wide range of native rhizobia, which often is high competitive and low efficient to N fixation (Santos et al, 2007;Thies et al, 1991). This is why it is difficult to establish an effective association between peanut and rhizobia .…”

Characterization of indigenous rhizobia from Caatinga

“…Arachis hypogaea (20) only in the morphologic analysis, but also in the restriction analysis of the 16S rDNA gene (Figures 2 and 3). M. tenuiflora isolates formed a consistent cluster both morphological and ARDRA analysis (Figures 2 and 3).…”