Ocorrência de bactérias diazotróficas em diferentes genótipos de cana-de-açúcar

Abstract

RESUMO -O objetivo deste trabalho foi avaliar a localização e o número de bactérias endofíticas em quatro genótipos de cana-de-açúcar e investigar sobre a possível existência de correlação com os resultados apresentados em trabalhos de quantificação da fixação biológica de nitrogênio (FBN). Fez-se um levantamento das bactérias diazotróficas presentes, e quantificou-se a população de Herbaspirillum spp. e Acetobacter diazotrophicus, em genótipos de cana-de-açúcar contrastantes quanto à capacidade de obter N da FBN. De acordo com o levantamento realizado neste trabalho, as bactérias estudadas (Azospirillum lipoferum, A. brasilense, A. amazonense, Herbaspirillum spp. e Acetobacter diazotrophicus) estavam presentes nos quatro genótipos avaliados e em todas as partes da planta, exceto A. amazonense, que não foi isolado de amostras de folhas. A quantificação das bactérias Herbaspirillum spp. e A. diazotrophicus mostrou não haver diferenças significativas entre os genótipos, e que, geralmente, elas estão presentes em maior número nas raízes. Enquanto Herbaspirillum spp. mantém-se mais estável ao longo do ciclo da cultura, a população de A. diazotrophicus decresce com a aproximação do final do ciclo comercial. Pode-se sugerir que as diferenças entre as taxas de FBN encontradas nos diversos genótipos não é causada por diferenças na presença ou no número das bactérias aqui estudadas. Termos para indexação: fixação de nitrogênio, Azospirillum, Acetobacter, Herbaspirillum. OCCURRENCE OF DIAZOTROPHIC BACTERIA IN DIFFERENT SUGAR CANE GENOTYPESABSTRACT -The objective of this work was to find out the localization and number of endophytic bacteria in four sugar cane genotypes and investigate upon the possible existence of correlation to the results obtained in some studies about quantification of biological nitrogen fixation (BNF). A survey of the diazotrophic bacteria present in sugar cane genotypes differing in their capacity to obtain nitrogen through BNF was performed, and population of Herbaspirillum spp. and Acetobacter diazotrophicus was quantified. The bacteria tested in the survey were Azospirillum lipoferum, A. brasilense, A. amazonense, Herbaspirillum spp. and Acetobacter diazotrophicus. All these bacteria were present in the four genotypes and were found in all parts of the plants, except A. amazonense which was not isolated from leaf samples. The quantification of Herbaspirillum spp. and A. diazotrophicus showed that there were no significant differences among the sugar cane genotypes and, generally, the bacteria were in greater number in roots. While number of Herbaspirillum spp. remained stable during the lifecycle of the culture, the population of A. diazotrophicus suffer a decrease with the approach of the end of the commercial cycle. It is suggested that the differences in the rates of BNF found in sugar cane genotypes are not caused by differences in the presence or the number of the bacterial species studied here. Index terms: nitrogen fixation, diazotrophy, Azospirillum, Acetobacter, Herbaspirillum. INTRODUÇ...

Diversity of plant growth-promoting bacteria associated with sugarcane

“…Interestingly, the high dominance of bacteria from the phylum Firmicutes (Bacillus and Paenibacillus) was found, and it disagrees with previous studies which found Proteobacteria (Burkholderia and Herbaspirilllum) as the most abundant phylum associated with sugarcane (Reis Junior et al, 2000). In contrast with a previous study (Broek and Vanderleyden, 1995), we did not find Azospirillum associated with the stalk and leaves of sugarcane, and the main reason would be that this genus presents occurrence in the rhizosphere.…”

Diversidade de Gluconacetobacter diazotrophicus isolada de plantas de cana-de-açúcar cultivadas no Brasil

“…ção nitrogenada. Altas aplicações de fertilizantes nitrogenados já foram sugeridas como responsáveis pela diminuição do número populacional de G. diazotrophicus em variedades de cana-de-açúcar cultivadas no México (Fuentes-Ramírez et al, 1999), Índia (Muthukumarasamy et al, 1999), Filipinas (Gonzalez & Barraquio, 2000) e Brasil (Reis Junior et al, 2000). Posteriormente foi observado que íons amônio inibem o cultivo deste organismo dentro dos tecidos de cana-de-açú-car (Muthukumarasamy et al, 2002 …”

Culture-independent analysis of endophytic bacterial communities associated with Brazilian sugarcane

“…Alternatives for improving crop production for this Poaceae and reducing carbon dioxide emissions are under intense investigation. Most of the studies of endophytic bacteria have focused on the isolation of diazotrophic endophytes, and the organisms frequently found are Gluconacetobacter diazotrophicus, Herbaspirillum spp and Azospirillum amazonense (Baldani et al, 1986;Reis Junior et al, 2000).…”

“…The organisms cited above (Baldani et al, 1986;Reis Junior et al, 2000;Fischer et al, 2011) were found in stems. Although this high prevalence of classic diazotrophic bacteria has been described in sugarcane, Magnani et al (2010) observed a dominance of Gammaproteobacteria, mainly from the families Pseudomonadaceae and Enterobacteriaceae in the stems of this plant.…”