Relationships between local variability in parasite communities of the black-spotted croaker (Protonibea diacanthus) (Teleostei: Sciaenidae) and host population structure and seasonality.

We evaluated spatial and temporal variability in parasite communities from the commercially important tropical marine fish the black-spotted croaker (Protonibea diacanthus) (Teleostei: Sciaenidae) to examine its population structure off the coast of the Northern Territory, Australia. Differences in parasite assemblage between four locations, across three seasons of the year, were used to evaluate the degree of connectivity of the sciaenid across coastal study areas. Analysis of parasite prevalence and mean intensity in these fish suggested the four sampling sites are distinct host populations. Across time, parasite assemblages at the four sites were distinct during the mid-dry (April-August) and build-up (September-November) seasons. During the wet season (December-March) there was substantial overlap in the parasite assemblages at three of the four sites indicating that fish population mixing may be occurring. Parasite assemblages at one nearshore site remained distinct across spatial and temporal scales. Our findings support the utility of parasitic organisms for elucidating the population structure of host species and reiterate the need to account for both spatial and temporal variability when performing stock discrimination analyses.

Banana Cultivar Field Screening for Resistance to Fusarium oxysporum f.sp. cubense Tropical Race 4 in the Northern Territory.

Fusarium oxysporum f.sp. cubense, causal agent of Panama disease, is one of the biggest threats to global banana production, particularly the Cavendish competent tropical race 4 (Foc TR4). It continues to spread globally with detections occurring in regions of the Middle East and new continents such as Africa and South America in the last decade. As the search was on for new management strategies and resistant cultivars to combat the disease, a banana cultivar-screening trial took place in the Northern Territory of Australia, which examined the responses of 24 banana cultivars to the soil borne fungus. These cultivars included material from TBRI, FHIA and selections from Thailand, Indonesia and Australia and evaluated for their resistance to tropical race 4 for two cropping cycles. Several cultivars displayed considerable resistance to Foc TR4, including several FHIA parental lines and hybrids, the Cavendish (AAA) selections GCTCV 215 and GCTCV 247 from TBRI and an Indonesian selection CJ19 showed either very little to no plant death due to the disease.

Strong population structure deduced from genetics, otolith chemistry and parasite abundances explains vulnerability to localized fishery collapse in a large Sciaenid fish, Protonibea diacanthus.

As pressure on coastal marine resources is increasing globally, the need to quantitatively assess vulnerable fish stocks is crucial in order to avoid the ecological consequences of stock depletions. Species of Sciaenidae (croakers, drums) are important components of tropical and temperate fisheries and are especially vulnerable to exploitation. The black-spotted croaker, Protonibea diacanthus, is the only large sciaenid in coastal waters of northern Australia where it is targeted by commercial, recreational and indigenous fishers due to its food value and predictable aggregating behaviour. Localized declines in the abundance of this species have been observed, highlighting the urgent requirement by managers for information on fine- and broad-scale population connectivity. This study examined the population structure of P. diacanthus across north-western Australia using three complementary methods: genetic variation in microsatellite markers, otolith elemental composition and parasite assemblage composition. The genetic analyses demonstrated that there were at least five genetically distinct populations across the study region, with gene flow most likely restricted by inshore biogeographic barriers such as the Dampier Peninsula. The otolith chemistry and parasite analyses also revealed strong spatial variation among locations within broad-scale regions, suggesting fine-scale location fidelity within the lifetimes of individual fish. The complementarity of the three techniques elucidated patterns of connectivity over a range of spatial and temporal scales. We conclude that fisheries stock assessments and management are required at fine scales (100 s of km) to account for the restricted exchange among populations (stocks) and to prevent localized extirpations of this species. Realistic management arrangements may involve the successive closure and opening of fishing areas to reduce fishing pressure.

DNA analysis of soil extracts can be used to investigate fine root depth distribution of trees.

Understanding the root distribution of trees by soil coring is time -: consuming as it requires the separation of roots from soil and classification of roots into particular size classes. This labour-intensive process can limit sample throughput and therefore sampling intensity. We investigated the use of quantitative polymerase chain reaction (qPCR) on soil DNA extractions to determine live fine root DNA density (RDD, mg DNA m(-2)) for mango (Mangifera indica) trees. The specificity of the qPCR was tested against DNA extracted from 10 mango cultivars and 14 weed species. All mango cultivars and no weeds were detected. Mango DNA was successfully quantified from control soil spiked with mango roots and weed species. The DNA yield of mango root sections stored in moist soil at 23-28 °C declined after 15 days to low concentrations as roots decayed, indicating that dead root materials in moist soil would not cause false-positive results. To separate large roots from samples, a root separation method for field samples was used to target the root fragments remaining in sieved (minimum 2 mm aperture) soil for RDD comparisons. Using this method we compared the seasonal RDD values of fine roots for five mango rootstock cultivars in a field trial. The mean cultivar DNA yields by depth from root fragments in the sieved soil samples had the strongest relationship (adjusted multiple R(2) = 0.9307, P < 0.001) with the dry matter (g m(-2)) of fine (diameter <0.64 mm) roots removed from the soil by sieving. This method provides a species-specific and rapid means of comparing the distribution and concentration of live fine roots of trees in orchards using soil samples up to 500 g.

The regionality of campylobacteriosis seasonality in New Zealand.

New Zealand has one of the highest incidences of campylobacteriosis in the developed world, which leads a global trend of increasing notifications of Campylobacter infections over the last decade. Foodborne and waterborne transmission have been implicated as significant mechanisms in the complex ecology of the disease in New Zealand. We examined both regional and temporal variation in notification rates to gain some insight into the role of the New Zealand environments in modifying disease incidence. Firstly, there is a marked difference in the seasonality of campylobacteriosis between the North and South Islands of New Zealand. The Far North and much of the rural North Island were found to display relatively low summer incidence and small inter-seasonal variation. Secondly, there appears to be a dispersed grouping of North Island urban areas, including Auckland, Hamilton, Napier and their hinterlands as well as a few areas on the South Island that exhibit higher summer incidence and more seasonality than the first group. Thirdly, Christchurch, Dunedin, much of the South Island and the lower North Island cities of Wellington and Upper Hutt appear to experience the highest summer incidence and strongest inter-seasonal variation in New Zealand. These three broad groupings of campylobacteriosis seasonality, constructed using a principal components analysis, suggest that the importance of transmission routes may vary regionally in New Zealand. The observed variation in seasonal incidence indicates a complex ecology that is unlikely to be explained by a single dominant transmission route across these three groupings.

Disease surveillance in rural communities is compromised by address geocoding uncertainty: a case study of campylobacteriosis.

This study illustrates the impact of address geocoding uncertainty on rural estimates of reportable disease incidence using campylobacteriosis as an example. After all cases of campylobacteriosis notified from 1993 to 1997 had been geocoded, the minimum and maximum disease notification rates were calculated for rural and urban areas of New Zealand. The estimated maximum rural rates were four times higher than estimated minimum rural rates, whereas estimated minimum and maximum urban rates varied minimally. The impact of address geocoding on the estimation of disease notification rates across Public Health Service Regions showed considerable variation. The relative proportions of ungeocoded notifications to rural notifications ranged from 1.3:1 to 10.2:1, reflecting the range of uncertainty in estimated rural rates of campylobacteriosis. Unless the reliability of captured rural address data is improved significantly, disease surveillance systems will underestimate rural rates of disease and limit small area analyses.