Suppressive effects of yard waste composts on Pythium spp. and Phytophthora spp. damping-off - a review about several research studies

In three long-term studies Yard Waste Composts (YWC) turned out to be sustainable suppressive to Pythium and Phytophthora root rot reducing the disease up to 98%. This was shown under lab and commercial conditions with composts from model and pilot-scale systems. Though suppression was related to microbial activity of the media we could not find a single microbial indicator for suppression over a wide range of samples. High quality YWC of different age showed distinct DNA fingerprints but similar suppressive effects. Thus, still it remains unclear what kind of microbial populations and functions are affecting disease suppression. However, non-destructive near-infrared spectroscopy (NIRS) turned out to predict suppression at least satisfactorily

Comparison of Barley Succession and Take-All Disease as Environmental Factors Shaping the Rhizobacterial Community during Take-All Decline▿

The root disease take-all, caused by Gaeumannomyces graminis var. tritici, can be managed by monoculture-induced take-all decline (TAD). This natural biocontrol mechanism typically occurs after a take-all outbreak and is believed to arise from an enrichment of antagonistic populations in the rhizosphere. However, it is not known whether these changes are induced by the monoculture or by ecological rhizosphere conditions due to a disease outbreak and subsequent attenuation. This question was addressed by comparing the rhizosphere microflora of barley, either inoculated with the pathogen or noninoculated, in a microcosm experiment in five consecutive vegetation cycles. TAD occurred in soil inoculated with the pathogen but not in noninoculated soil. Bacterial community analysis using terminal restriction fragment length polymorphism of 16S rRNA showed pronounced population shifts in the successive vegetation cycles, but pathogen inoculation had little effect. To elucidate rhizobacterial dynamics during TAD development, a 16S rRNA-based taxonomic microarray was used. Actinobacteria were the prevailing indicators in the first vegetation cycle, whereas the third cycle—affected most severely by take-all—was characterized by Proteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, and Acidobacteria. Indicator taxa for the last cycle (TAD) belonged exclusively to Proteobacteria, including several genera with known biocontrol traits. Our results suggest that TAD involves monoculture-induced enrichment of plant-beneficial taxa

Response of soil microbial communities to different management practices in surface soils of a soybean agroecosystem in Argentina

Argentina is the world’s third most important soybean producer; hence, there is an urgent need to preserve soil health by applying appropriate agricultural practices to maintain sustainable production in the upcoming years. Because productivity of agricultural systems largely depends on soil microbial processes, the influence of different management strategies on soil microbial community structure was analyzed in a long-term field trial started in 1992. The experimental design was a split-plot arrangement of treatments, consisting in two tillage treatments: zero tillage (ZT) and reduced tillage (RT), in combination with two crop rotation treatments: soybean monoculture (SS) and corn-soybean (CS). Phospholipid fatty acid (PLFA) profiles were used to assess total microbial community structure. Denaturing gradient gel electrophoresis (DGGE) profiles of 18S rRNA were generated to describe the influence of crop practices on fungal communities. Total PLFA content was lowest in soil under reduced tillage and soybean monoculture; therefore the use of reduced tillage-soybean monoculture in agroecosystems might produce important reductions in total microbial biomass. The structure of total microbial communities, as estimated by PLFA, was affected by crop rotation. Moreover, the fungal communities, as estimated by DGGE analysis, were influenced by combined effects of crop rotation and tillage system.Fil: Vargas Gil, Silvina. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigaciones de Ciencias Veterinarias y Agronómicas. Instituto de Fitopatologia y Fisiologia Vegetal; ArgentinaFil: Meriles, Jose Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Conforto, C.. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigaciones de Ciencias Veterinarias y Agronómicas. Instituto de Fitopatologia y Fisiologia Vegetal; ArgentinaFil: Basanta, María del Valle. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuaria Manfredi; ArgentinaFil: Radl, Vivianne. Helmholtz Zentrum Munich. Institute of Soil Ecology; AlemaniaFil: Hagn, Alexandra. Helmholtz Zentrum Munich. Institute of Soil Ecology; AlemaniaFil: Schloter, Michael. Helmholtz Zentrum Munich. Institute of Soil Ecology; AlemaniaFil: March, Guillermo. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigaciones de Ciencias Veterinarias y Agronómicas. Instituto de Fitopatologia y Fisiologia Vegetal; Argentin

Changes in fungal community composition in response to vegetational succession during the natural regeneration of cutover peatlands

Despite the importance of peatlands as a major store of sequestered carbon and the role of fungi in releasing sequestered C, we know little about the community structure of fungi in peatlands. We investigated these across a gradient of naturally regenerating peatland vegetation using denaturing gradient gel electrophoresis (DGGE) and clone libraries of fragments of the fungal rRNA internal transcribed spacer (ITS) region. Significant changes in the fungal community structure of peat samples at different stages of regeneration were observed, which relate to the composition of the vegetation recolonizing these sites. Cloning and sequence analysis also demonstrated a potential shift in the relative abundance of the main fungal phyla. Some of the clones identified to genus level were highly related to fungi known to play a role in the degradation of plant litter or wood in similar ecosystems and/or form mycorrhizal associations. In addition, several fungal isolates highly related to peat clones were obtained, and their enzymic capacity to degrade structural plant tissues was assessed. Together, these results suggest that the fungal community composition of peat may be an important indicator of the status of regeneration and potential carbon sequestration of cutover peatlands