Gas chromatographic determination of captan, folpet, and captafol residues in tomatoes, cucumbers, and apples using a wide-bore capillary column: interlaboratory study.

An interlaboratory study of the determination of captan, folpet, and captafol in tomatoes, cucumbers, and apples was conducted by 4 laboratories using wide-bore capillary column gas chromatography with electron capture detection. The 3 fungicides were determined using the Luke et al. multiresidue method modified to include additional solvent elution in the optional Florisil column cleanup step used with this method. The crops were fortified with each fungicide at 3 levels per crop. Mean recoveries ranged from 86.2% for a 25.1 ppm level of captan in apples to 115.4% for a 0.288 ppm level of captafol in apples. Interlaboratory coefficients of variation ranged from 3.4% (24.7 ppm folpet) to 9.7% (0.243 ppm captafol) for tomatoes; from 2.8% (2.0 ppm captafol) to 8.2% (24.8 ppm captan) for cucumbers; and from 1.5% (0.234 ppm folpet) to 22.1% (0.266 ppm captafol) for apples.     

Ion-pairing liquid chromatographic determination of benzimidazole fungicides in foods

A method is described for determining residues in foods of thiabendazole, thiophanate methyl, the di-oxygen analogue metabolite [dimethyl 4,4'-O-phenylene bis (allophanate)] that is the metabolite name of the latter, and methyl-2-benzimidazole carbamate, which is the major metabolite and fungitoxic principle common to both thiophanate methyl and benomyl. The residues are extracted from the product using methanol and are partitioned into dichloromethane after initial acidification and again after subsequent alkalinization of the extract. Residues are separated and quantified by reverse-phase liquid chromatography using an ion-pairing mobile phase with UV and fluorescence detectors in tandem. Recoveries from 7 different food crops fortified at 0.2-35 ppm levels ranged from 64 to 105%.     

Capturing genetic diversity of wild populations for <Emphasis Type="Italic">ex situ</Emphasis> conservation: Texas wild rice (<Emphasis Type="Italic">Zizania texana</Emphasis>) as a model

Genebanks complement other conservation programs because they preserve genetic diversity needed for future breeding and restoration. We evaluated efficiency of capturing genetic diversity, using endangered Zizania texana (Texas wild rice) as a model for plants with recalcitrant seeds. This perennial aquatic grass is restricted to 4 km of the San Marcos River in Texas. An early conservation collection included plants from stands throughout the river, based on the assumption stands would be unique genotypes. Using microsatellite markers, we found that genetic diversity was concentrated in five of 15 large, demographically stable stands; 96 stands smaller than 2 m² contributed no unique alleles. High heterozygosity and few duplicate genotypes suggested that sexual reproduction occurs more often than presumed. Simulations of stratified sampling of large stands captured all alleles in only 45 individuals, while random sampling along the river captured much less diversity. The early conservation collection captured as much diversity as expected from random sampling. Texas wild rice stands resemble a mainland-island metapopulation; our analyses suggest that stratified sampling maximizes genetic diversity for this population dynamic. Demographic and genetic information is important for validating the design of efficient ex situ collections and guiding in situ conservation.     

Response of Ulmus americana seedlings to varying nitrogen and water status. 1 Photosynthesis and growth

Well-watered American elm (Ulmus americana L.) seedlings responded to increased nitrate availability with increased leaf nitrogen (N) concentration and photosynthetic rate, larger and more numerous leaves, greater total growth and greater proportional allocation of carbon to shoot than root. Plasticity of growth and carbon allocation were greater than plasticity of N concentration and photosynthetic capacity. For a given N availability, allocation of N per unit leaf area was positively correlated with dry mass per unit leaf area (specific leaf mass), but these relationships differed with N availability. Rates of net photosynthesis and leaf conductance declined logarithmically with decreasing predawn water status. Increased water stress resulted in a greater relative decline in net photosynthesis and leaf conductance for high-N than low-N plants.     

Correlations between ground and excited state spectra of a quantum Dot

The ground and excited state spectra of a semiconductor quantum dot with successive electron occupancy were studied with linear and nonlinear magnetoconductance measurements. A direct correlation was observed between the mth excited state of the N-electron system and the ground state of the (N + m)-electron system for m up to 4. The results are consistent with a single-particle picture in which a fixed spectrum of energy levels is successively filled, except for a notable absence of spin degeneracy. Further departures from the single-particle picture due to electron-electron interaction were also observed. Magnetoconductance fluctuations of ground states show anticrossings where wave function characteristics are exchanged between adjacent levels.     

A Legume Ethylene-Insensitive Mutant Hyperinfected by Its Rhizobial Symbiont

Development of the Rhizobium-legume symbiosis is controlled by the host plant, although the underlying mechanisms have remained obscure. A mutant in the annual legume Medicago truncatula exhibits an increase of more than an order of magnitude in the number of persistent rhizobial infections. Physiological and genetic analyses indicate that this same mutation confers insensitivity to the plant hormone ethylene for multiple aspects of plant development, including nodulation. These data support the hypothesis that ethylene is a component of the signaling pathway controlling rhizobial infection of legumes.     

Effects of fire and fire intensity on the germination and establishment of Acacia karroo, Acacia nilotica, Acacia luederitzii and Dichrostachys cinerea in the field

Background

The native annual tobacco, Nicotiana attenuata, is found primarily in large ephemeral populations (typically for less than 3 growing seasons) after fires in sagebrush and pinyon-juniper ecosystems and in small persistent populations (for many growing seasons) in isolated washes typically along roadsides throughout the Great Basin Desert of the SW USA. This distribution pattern is due to its unusual germination behavior. Ephemeral populations are produced by the germination of dormant seeds from long-lived seed banks which are stimulated to germinate by a combination of unidentified positive cues found in wood smoke and the removal of inhibitors leached from the unburned litter of the dominant vegetation. Persistent populations may result where these inhibitors do not exist, as in washes or along disturbed roadsides. To determine if this germination behavior has influenced population structure, we conducted an AFLP (244 individuals), ISSR (175 individuals) and ISSR+ AFLP (175 individuals) analysis on plants originating from seed collected from populations growing in 11 wash and burns over 11 years from the SW USA.

Results

Genetic variance as measured by both ISSR and AFLP markers was low among sites and comparatively higher within populations. Cluster analysis of the Utah samples with samples collected from Arizona, California, and Oregon as out-groups also did not reveal patterns. AMOVA analysis of the combined AFLP and ISSR data sets yielded significantly low genetic differentiation among sites (Φct), moderate among populations within sites (Φsc) and higher genetic differentiation within populations (Φst).

Conclusions

We conclude that the seed dormancy of this post-fire annual and its resulting age structure in conjunction with natural selection processes are responsible for significantly low among sites and comparatively high within-population genetic variation observed in this species.     

Temporal segregation in spawning between native Yellowstone cutthroat trout and introduced rainbow trout

Hybridisation with introduced taxa poses a threat to native fish populations. Mechanisms of reproductive isolation can limit or prevent hybridisation between closely related species. Understanding how these mechanisms interact between the same species across geographically distinct occurrences of secondary contact, and how regional factors influence them, can inform our understanding of hybridisation as a threat and management actions to mitigate this threat. We used data collected on adult fish migration timing and approximate emergence timing of subsequent juvenile fish paired with genomic data to assess whether temporal isolation in the timing of spawning exists between Yellowstone cutthroat trout, rainbow trout and hybrids in the North Fork Shoshone River drainage in northwest Wyoming. We found evidence that Yellowstone cutthroat trout spawn, on average, two to four weeks later than rainbow trout and hybrids and two environmental covariates related to water temperature and discharge were associated with differences in spawning migration timing. Despite statistical support for Yellowstone cutthroat trout spawning later, disproportionately high numbers of rainbow trout and hybrids, paired with extended spawning seasons, lead to substantial overlap between all genotypes. Our results provide further evidence of temporal segregation in the timing of spawning as a mechanism of reproductive isolation between closely related species, but substantial spawning overlap suggests temporal segregation alone will not be enough to curtail hybridisation in conservation populations.