Effect of sorghum seedlings, and previous crop, on soil fluorescent Pseudomonas spp.

Abstract

Hypotheses in which sorghum seedlings [Sorghum bicolor (L.) Moench] of different genotypes will differentially modify soil microorganisms and will affect subsequent planting of wheat (Triticum aestivum L.) seedlings, were tested. Wheat cultivar Lewjain, and sorghum genotypes Redlan and RTx433, were planted into soils previously planted with wheat or sorghum in growth chamber experiments. Total culturable fungi and oomycetes, and fluorescent Pseudomonas spp. numbers (cfu) were determined. Pseudomonads were screened for hydrogen cyanide (HCN) production, for the presence of the phlD gene for 2,4-diacetylphloroglucinol production (Phl) and for a region of the operon involved in phenazine-1-carboxylic acid (PCA) production. Pasteurized soils were inoculated with rifampicin-marked strains of Pseudomonas fluorescens then planted with Lewjain, Redlan and RTx433 to assess rhizosphere and soil colonization. Effects of plant species, sorghum genotype and previous crop on culturable fungi and oomycetes, and pseudomonad numbers (cfu g −1 soil) were statistically significant. Soils planted with RTx433 or Lewjain had greater numbers of fungal cfu than soils planted with Redlan. When Lewjain seedlings were grown in soil previously planted with RTx433, there were greater numbers of fungal cfu than when Lewjain was planted into Redlan soil. Wheat planted into wheat soil resulted in statistically significantly fewer numbers of pseudomonads than when planted into sorghum soil. Overall, percentages of HCN-producing pseudomonads increased, especially when wheat seedlings were planted in wheat soil. For most treatments, percent of isolates with Phl declined, except when Redlan was planted into Redlan soil, which resulted in increased Phl isolates. When rifampicin-marked P. fluorescens isolates were applied to pasteurized soil, sorghum seedlings sustained rhizosphere and soil populations similar to those on wheat. Sorghum genotypes may differ in associations with soil microorganisms, Plant Soil

Diversity and Activity of Free-Living Nitrogen-Fixing Bacteria and Total Bacteria in Organic and Conventionally Managed Soils

“…Any changes to the microbial community are attributed to changes in organic root exudates affecting microbial activity in a species-specific manner (18,51). In this study, these changes were detected in the bulk soil and were apparent even though the crop was the same in both rotations in the sampling year.…”

Soil and root populations of fluorescent Pseudomonas spp. associated with seedlings and field-grown plants are affected by sorghum genotype

“…Recently, we provided evidence suggesting that when sorghum seedlings preceded wheat seedlings in a crop sequence, sorghum genotype influenced the characteristics of fluorescent Pseudomonas spp. populations in bulk soil (Funnell-Harris et al 2008). That root exudates of sorghum genotypes Redlan and RTx433 differed had been shown by studies in which seedlings differentially produced the benzoquinone root exudate, sorgoleone: of 25 genotypes tested, Redlan produced the greatest amount while RTx433 produced the least (approx.…”

“…18 versus 1 mg per g root fresh weight) (Nimbal et al 1996). Although this compound is technically challenging to detect in rhizospheres of soil-grown plants (Weidenhamer 2005), previous studies have suggested that genotypespecific differences in sorghum root exudates may affect soil microbial communities (Kipe-Nolt et al 1985;Funnell-Harris et al 2008). The turnover of applied sorgoleone to native soils indicated that microorganisms utilize this compound as an energy source, which suggests a possible mechanism of how sorgoleone may influence soil microbial communities (Gimsing et al 2009).…”

“…During cycling of seedlings in growth chamber bioassays, wheat cultivar Lewjain preceded or succeeded cycling of sorghum genotypes RTx433 and Redlan, and changes in characteristics of fluorescent Pseudomonas spp. were monitored in soils at the end of each cycle (Funnell-Harris et al 2008). Traits potentially involved in biological control, including 2,4-DAPG, indirectly detected by PCR amplification of phlD gene (phl), and hydrogen cyanide production (HCN), detected by a colorimetric assay, were assessed (Funnell-Harris et al 2008;Raaijmakers et al 1997).…”

Sorgoleone: benzoquinona lipídica de sorgo com efeitos alelopáticos na agricultura como herbicida

“…Metabólitos secundários que são depositados no solo pelos exsudados ou pela morte das plantas fornecem uma rica fonte de carbono que é utilizada por populações microbianas do solo (belz, 2007). Esses metabólitos influenciam a composição microbiana da rizosfera afetando as plantas que interagem com ela FuNNell-harris et al, 2008). Por outro lado, em alguns casos, micro-organismos da rizosfera podem favorecer a degradação de certos compostos alelopáticos diminuindo, assim, sua fitotoxicidade, particularmente nos casos de ácidos fenólicos.…”