A life cycle sustainability assessment (LCSA) of oxymethylene ether as a diesel additive produced from forest biomass

The International Journal of Life Cycle Assessment - Due to efforts to reduce dependence on limited fossil energy reserves and increasing GHG emissions related to fossil fuel extraction and use in...     

Effects of drought stress and arbuscular mycorrhiza on the growth of Gliricidia sepium (Jacq). Walp, and Leucaena leucocephala (Lam.) de Wit. in simulated eroded soil conditions

A greenhouse investigation was conducted to determine the effect of arbuscular mycorrhiza and drought on the growth of two tropical hedgerow legume trees (Gliricidia sepium and Leucaena leucocephala) under simulated eroded soil conditions. It was a factorial design with two levels of watering regime (adequate watering and drought), inoculation with Glomus deserticola (with and without), and two soil types (0-30 cm topsoil and 30-60 cm subsoil). Each treatment was replicated 3 times. After ten drought cycles, the growth of Gliricidia sepium in the subsoil was enhanced by mycorrhizal inoculation under both watering regimes whereas there was no significant contribution of mycorrhizal inoculation to the growth of L. leucocephala in both soil types under the two watering regimes. Drought stress significantly reduced most growth parameters for the two tree species in both soils with or without fungal inoculation. The N-fixing activity of Gliricidia sepium benefited from Glomus deserticola inoculation while that of L. leucocephala was not significantly affected in the topsoil. Mycorrhizal colonization was reduced for both tree species in the subsoil compared to the topsoil while it was significantly increased for both species in the subsoil when compared to the uninoculated subsoil counterpart. In the subsoil, inoculation of Gliricidia sepium with the mycorrhizal fungus increased root colonization by 89% and 73% under adequate watering and drought, respectively, whereas L. leucocephala had only a 38% and 42% increase in root colonization under comparative conditions in the subsoil. Thus Glomus deserticola inoculation may be beneficial to the growth of Gliricidia sepium in a badly eroded site where topsoil is missing.     

Dynamics of Fungal Communities in Bulk and Maize Rhizosphere Soil in the Tropics

The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants.     

Two Genetically Distinct Populations of Colletotrichum gloeosporioides Penz. Causing Anthracnose Disease of Yam (Dioscorea spp.)

Variation within Colletotrichum gloeosporioides, the causal agent of yam anthracnose disease, is still poorly defined and this hinders breeding for resistance. Two morphotypes of C. gloeosporioides, designated slow‐growing grey (SGG) and fast‐growing salmon (FGS), are associated with anthracnose disease of yam in Nigeria. The morphotypes are distinguishable based on colony and conidial morphology, growth rate, virulence, as well as vegetative compatibility, but molecular differentiation of SGG and FGS strains is needed to facilitate epidemiological studies. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)‐amplified small subunit (18S) rDNA fragments, and microsatellite‐primed PCR (MP‐PCR) genomic fingerprinting were employed to provide a basis for molecular differentiation of the morphotypes. DGGE analysis revealed patterns that clearly differentiated isolates of the aggressive defoliating SGG from the moderately virulent non‐defoliating FGS strains. Genetic analysis based on 52 MP‐PCR markers revealed highly significant differentiation between the SGG and FGS populations on yam (G_ST = 0.22; Nei's genetic identity = 0.85; θ = 0.28, P < 0.001), indicating that the SGG and FGS morphotypes represent genetically differentiated populations. The results of the molecular typing using DGGE and MP‐PCR analyses were consistent with the disease phenotype caused by the two morphotypes. Consequently, these molecular techniques might be used, at least partly, to replace time‐consuming virulence studies on yam.     

Dynamics of fungal communities in bulk and maize rhizosphere soil in the tropics

The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants.