Water,salt and nutrient fluxes of tropical tidal salt flats

The water budget of a tropical tidal salt flat in dry tropical Australia has been studied with particular emphasis on estimating the groundwater fluxes. Salt was used as a passive tracer to determine some of these fluxes. Groundwater salt accumulation (or loss) was less than 1 kg/m³/month. Surface water leaving the flat at a higher salt concentration than flood water causes a net outwelling of salt of between 0.4 and 1 kg/m²/month. Evaporation from the salt flat was estimated to be 70 mm/month. Using these measurements and a simple model of the groundwater flows, it is concluded that the groundwater loss is less than 40 mm/month. The accuracy of the salt budget was insufficient to rule out the possibility that the net groundwater motion was upwards. Measurements of Si and PO_{_4} fluxes indicated that the net outwelling due to surface water flows were respectively 3 mmole/m²/month and 0.014 mmole/m²/month. A net groundwater loss of 10 mm would produce a similar magnitude outwelling due to groundwater discharge. The mangrove-fringed tropical tidal salt flats are the source of large quantities of nutrients that are released to the near-shore zone.     

Relationship between cultivar height and severity of Fusarium ear blight in wheat

A significant negative relationship between tiller height and resistance to Fusarium ear blight (FEB), following inoculation, was observed in 17 cultivars of winter wheat in the 1995/96 growing season. Tall cultivars such as Kraka and Spark showed fewer symptoms of FEB (6 and 4%) than the shorter cultivars Brigadier and Virtue (35 and 51%). To determine if this relationship was caused by a genetic association or an effect of the microclimate, height and disease were measured in segregating populations derived from tall × short cultivars and humidity was measured in near-isogenic lines with and without the Rht1 and Rht2 dwarfing genes. Among random F₃ populations there was a clear tendency for tall strawed lines to show less severe disease symptoms than shorter strawed lines following inoculation. The effect of the individual dwarfing genes Rht1 and Rht2 on the severity of FEB was also studied in an inoculation trial using a number of near-isogenic lines of Maris Huntsman and Maris Widgeon. Within isogenic lines of Maris Huntsman, there was a clear tendency for tall straw to be associated with fewer symptoms, but this was not apparent within lines of Maris Widgeon. Monitoring relative humidity at ear height in a short and tall isogenic line of Maris Huntsman revealed no significant differences between these genotypes from GS 65 to GS 85, suggesting that microclimate cannot explain differences in severity of FEB between these lines. It is suggested that there are independent genes affecting the severity of FEB that may allow plant breeders to select resistant cultivars of any height.     

Evaporation over a tropical tidal salt flat

Measurements of temperature, wind speed and humidity within 6 mof the surface of a mangrove-fringed tidal tropical salt flatwere performed. Using the aerodynamic method, this data was usedto infer evaporation rates from the salt flat. For a few daysafter tidal inundation or rain, the salt flats were wet andevaporation rates of about 5×10^-3 m day^-1 prevailed. By 8 daysafter tidal inundation and with no rain, evaporation rates haddropped to less than 2×10^-3 m day^-1. The monthly evaporation ratewas about 7×10^-2 m. This generates high salinity which, togetherwith surface temperatures exceeding 50°C, prevents colonisationof these areas by mangroves.     

Quarantine protects Falkland Islands (Malvinas) cats from feline coronavirus infection

Feline coronavirus (FCoV) causes feline infectious peritonitis (FIP). Since 2002, when 20 cats on the Falkland Islands were found to be FCoV seronegative, only seronegative cats could be imported. Between 2005-2007, 95 pet and 10 feral cats tested negative by indirect immunofluorescence antibody (IFA) analysis using two strains of type II FCoV, two transmissible gastroenteritis virus assays, an enzyme-linked immunosorbent assay and rapid immunomigration test. Twenty-four samples (23%) showed non-specific fluorescence, mostly attributable to anti-nuclear antibodies (ANA). The reason for ANA was unclear: reactive samples were negative for Erhlichia canis antibodies; seven were feline immunodeficiency virus positive, but 15 were negative. It was not possible to determine retrospectively whether the cats had autoimmune disease, hyperthyroidism treatment, or recent vaccination which may also cause ANA. The FCoV/ FIP-free status of the Falkland Islands cats should be maintained by FCoV testing incoming cats. However, ANA can complicate interpretation of IFA tests.     

Differential seedling resistance to the eyespot pathogens,Oculimacula yallundae and Oculimacula acuformis,conferred by Pch2 in wheat and among accessions of Triticum monococcum

Eyespot is an economically important stem‐base disease of wheat caused by two fungal species: Oculimacula yallundae and Oculimacula acuformis. This study investigated the efficacy of two sources of resistance, viz. the genes Pch1, introgressed into hexaploid wheat from Aegilops ventricosa, and Pch2, identified in wheat cv. Cappelle Desprez, against O. yallundae and O. acuformis separately. In a series of seedling bioassays Pch1 was found to be highly effective against both species. Although Pch2 was found to confer resistance against both pathogen species, it was significantly less effective against penetration from O. yallundae than O. acuformis. Furthermore, a quantitative trait locus (QTL) analysis was not able to locate any resistance to O. yallundae on chromosome 7A of Cappelle Desprez. This has important implications for the use of Pch2 in commercial cultivars as it is necessary to have genes that confer resistance to both pathogens for effective eyespot control. In addition, a set of 22 T. monococcum accessions was screened for resistance to both O. yallundae and O. acuformis to identify potentially novel resistances and to assess the accessions for evidence of differential resistance to the eyespot species. Significant differences in resistance to the two pathogens were identified in four of these lines, providing evidence for differential resistance in T. monococcum. This study demonstrates that future screening for novel sources of eyespot resistance should investigate both pathogen species.     

Location of a Gene for Resistance to Eyespot (Pseudocercosparella herpotrichoides) on Chromosome 7D of Bread Wheat

Chromosome 7D of the wheat line VPM1 derived from a cross of Aegilops ventricosa with wheat confers resistance to the facultative fungal parasite Pseudocercosporella herpotrichoides. To determine the number of genes responsible fur this resistance, homozygous recombinant lines were developed from an F₁ between the wheat variety ‘Hobbit sib’ and a substitution line carrying chromosome 7D of VPM1 in a ‘Hobbit sib’ background. Resistance to Pseudocercosporella herpotrichoides is shown to be determined by a single gene located distally on the long arm of chromosome 7D. EpD1b, a unique allele of a gene encoding the readily detectable isoenzyme — endopeptidase, maps without recombination to Pch1 suggesting for two separate genes a maximum recombination value of 0.03 (P 0.05). Resistance to Pherpotrichoides could alter-natively be a product of Ep-D1b. Pch1 is also mapped against a gene for adult plant resistance to brown rust (Puccinia recondita), to Rc3 which confers coleoptile colour, and to α-Amy-D2, an isozyme that encodes α-amylase production.