We explored whether extracts of trees frequently found associated with amphibian habitats in Australia and Arizona, USA, may be inhibitory to the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has been associated with global amphibian declines. We used salamanders Ambystoma tigrinum as the model system. Salamanders acquired significantly lower loads of Bd when exposed on leaves and extracts from the river red gum Eucalyptus camaldulensis, and loads were also low in some animals exposed on extracts of 2 oak species, Quercus emoryi and Q. turbinella. Some previously infected salamanders had their pathogen loads reduced, and some were fully cured, by placing them in leaf extracts, although some animals also self cured when housed in water alone. A significant number of animals cured of Bd infections 6 mo earlier were found to be resistant to reinfection. These results suggest that plants associated with amphibian habitats should be taken into consideration when explaining the prevalence of Bd in these habitats and that some amphibians may acquire resistance to the fungus if previously cured.
Identifying physiological maturity (PM) in sunflower (Helianthus annuus L.) by visual methods is subjective. The present study was conducted during two years in two short season sunflower hybrids (Macón and MG60) to determine the relationship between quantitative color parameters in the receptacle and physiological markers such as fruit dry weight (FDW) and fruit water content (FWC) from flowering to PM. Fruits from the external 25% of the capitulum radius were sampled at 3-5-day intervals from first anthesis until harvest maturity. Fruit and receptacle fresh and dry weight were calculated, and color changes of the receptacle base were followed over time using a spectrophotometer. Comparison of colorimetric coordinates a* and b*, defined by the CIELAB color space enabled quantitative correlation of color changes in the receptacle with the maturation stage of the fruits and their moisture content. In both hybrids and years, fruits attained maximum dry weight when the receptacle color turned from dark green to buttery-yellow. Strong correlations were found between FWC and a* for Macón the first (r = -0.877) and second year (r = -0.934) and for MG60, (r = -0.912 and r = -0.891) the first and second year, respectively. The same results were found for b* for Macón (r = -0.901 and r = -0.829) and for MG60 (r = -0.898 and r = -0.863) for the first and second year respectively. Maximum b* at FWC between 40 to 41% had the highest correlation with maximum fruit dry weight for both hybrids and years, and was a good indicator for identifying the attainment of PM. This work represents an original contribution and a first step towards the development of a model for predicting PM in sunflower by using colorimetric measurements.
Phloem necrosis (PN), caused by a submicroscopic mycoplasmalike organism, is lethal in five elm (U/mus) species native to North America. All American elms, including those resistant to Dutch elm disease, are highly susceptible. The causal organism, which has never been cultured apart from plant or insect hosts, spreads within infected trees only within phloem sieve tubes. Infected red (slippery) elm, less susceptible than American elm, develops witches' brooms before dying. Elms of European and Asiatic origin seem resistant. The causal agent was graft transmitted to clones of two European species, U. carpinifolia and U. hollandica, in which only witches' brooms developed, while no symptoms have yet been induced in Scotch {U. glabra) or Siberian [U. pumila) elms. The PN agent is naturally transmitted by adults of the white banded elm leafhopper, Scaphoideus luteolus, and possibly by other leafhoppers or planthoppers that feed on elm. PN epidemics are usually localized. In northern areas the disease is unknown where average minimum winter temperature is lower than -15 deg. F (-26 deg. C). Remissions of PN symptoms have occurred after trunk injections with tetracycline solutions in Mississippi and New York; but in northern areas death occurs so soon after first display of symptoms that therapy of infected trees may prove impractical on account of the low success rate. Protective antibiotic treatments have not been tested. No elm population has yet been preserved in the simultaneous presence of PN and Dutch elm disease.
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