- D. Helmig (1)
- T.A.J. Lee van der (1)
- B.L. Lefer (1)
- S. Meinardi (1)
- A.L. Swanson (1)
- C. Waalwijk (1)
- Jin Xu (1)
- Jingsheng Xu (1)
- Y. Zhang (1)
- H. Zhang (1)
Population Analysis of the Fusarium graminearum Species Complex from Wheat in China Show a Shift to More Aggressive Isolates
Zhang, H. ; Lee, T.A.J. van der; Waalwijk, C. ; Chen, W. ; Xu, Jin ; Xu, Jingsheng ; Zhang, Y. ; Feng, J. - \ 2012
PLoS One 7 (2012)2. - ISSN 1932-6203 - 13 p.
head blight pathogen - multilocus genotype data - genealogical concordance - mycotoxin chemotypes - genetic diversity - gibberella-zeae - eastern china - f-asiaticum - clade - scab
A large number of Fusarium isolates was collected from blighted wheat spikes originating from 175 sampling sites, covering 15 provinces in China. Species and trichothecene chemotype determination by multilocus genotyping (MLGT) indicated that F. graminearum s. str. with the 15-acetyl deoxynivalenol (15ADON) chemotype and F. asiaticum with either the nivalenol (NIV) or the 3-acetyl deoxynivalenol (3ADON) chemotype were the dominant causal agents. Bayesian model-based clustering with allele data obtained with 12 variable number of tandem repeats (VNTR) markers, detected three genetic clusters that also show distinct chemotypes. High levels of population genetic differentiation and low levels of effective number of migrants were observed between these three clusters. Additional genotypic analyses revealed that F. graminearum s. str. and F. asiaticum are sympatric. In addition, composition analysis of these clusters indicated a biased gene flow from 3ADON to NIV producers in F. asiaticum. In phenotypic analyses, F. asiaticum that produce 3ADON revealed significant advantages over F. asiaticum that produce NIV in pathogenicity, growth rate, fecundity, conidial length, trichothecene accumulation and resistance to benzimidazole. These results suggest that natural selection drives the spread of a more vigorous, more toxigenic pathogen population which also shows higher levels of fungicide resistance
Release and uptake of volatile inorganic and organic gases through the snowpack at Niwot Ridge, Colorado
Helmig, D. ; Apel, E. ; Blake, D. ; Ganzeveld, L.N. ; Lefer, B.L. ; Meinardi, S. ; Swanson, A.L. - \ 2009
Biogeochemistry 95 (2009)1. - ISSN 0168-2563 - p. 167 - 183.
atmospheric methyl-bromide - carbonyl sulfide ocs - coastal salt-marsh - eastern china - air - soil - exchange - greenland - fluxes - summit
Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO2), chloroform (CHCl3), dimethylsulfide (CH3)2S, carbondisulfide (CS2), and dichlorobromomethane (CHBrCl2), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH3Cl), methylbromide (CH3Br), dibromomethane (CH2Br2), bromoform (CHBr3), tetrachloromethane (CCl4), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.