Background and aims Some elephant grass (Pennisetum purpureum) genotypes are able to produce large amounts of biomass and accumulate N derived from BNF when growing in soil with low N levels. However, information about the diazotrophic bacteria colonizing this C4 plant is still very scarce. This study aimed to characterize the plant growth promoting traits of a fraction of culturable diazotrophs colonizing the genotypes CNPGL F06-3 and Cameroon. Methods A total of 204 isolates were obtained from surface sterilized leaves, stems and roots after culturing on five different N-free semisolid media. These were then analyzed by BOX-PCR, and the 16S rRNA and nifH sequences of representative isolates were obtained. The functional ability of the isolates to reduce acetylene, produce indole and to solubilize phosphate was also determined. Results The diazotrophic bacterial population varied from 10 2 up to 10 6 bacteria g −1 fresh tissues of both genotypes. The BOX-PCR analysis suggested a trend in the genetic diversity among the 204 diazotrophic strains colonizing the different genotypes and plant tissues. Sequencing of 16S rRNA fragments confirmed the presence of Azospirillum brasilense and Gluconacetobacter diazotrophicus and revealed for the first time the occurrence of G. liquefaciens, G. sacchari, Burkholderia silvatlantica, Klebsiella sp., Enterobacter cloacae and E. oryzae in elephant grass. Interestingly, several nifH sequences from isolates identified as G. liquefaciens and G. sacchari showed homologies with nifH sequences of Enterobacter species. The majority of the isolates (97%) produced indole compounds, 22% solubilized phosphate and 6.4% possessed both characteristics.
Often unable to regenerate naturally, areas degraded by ore tailings must follow measures aimed at their environmental recovery. The revegetation and the use of bio-stimulants can contribute to the improvement of soil fertility leading to increased production of plant biomass and the cycling of nutrients between soil-plant.The objective was to evaluate the dry matter production, accumulation and nutrient export rates by pig beanplants (Canavalia ensiformis) and Crotalaria juncea cv. IAC-KR-1 as a function of the application of humic substances and diazotrophic bacteria. The experiment was conducted in a greenhouseusing iron ore tailings as substrate. An experimental design of random blocks (4x3x2) was used with four repetitions, four doses of humic substances, applied at 3 different times, with or without inoculation of diazotrophic bacteria. The supply of humic substances and mainly the inoculation in both species increased the dry matter production, reaching 70% of the average increase in pig beans. Inoculation in pig bean plants increased the absorption and transfer factor of Fe and P, and reduced the transfer factor of K, Ca and Mg, and in crotalaria plants increased the absorption of Mg, P and Mn, and reduced the absorption of Fe. The high content of Fe in mining tailings culminated in high absorption and mobilization of this element in the roots of the plants as an alternative to minimize toxic effects caused by its excess.
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