Regions Of Southern Australia Research Articles

The Influence of Grapevine Cultivar and Isolate of Eutypa lata on Wood and Foliar Symptoms.

Grapevine cultivar (Vitis vinifera) and isolate of Eutypa lata influence wood and foliar symptoms of Eutypa dieback. Foliar symptoms of Eutypa dieback developed within 8 months of inoculating young grapevines (cvs. Grenache, Cabernet Sauvignon, and Merlot) in a shadehouse. Isolates of E. lata from various wine regions in southern Australia varied in their ability to colonize inoculated grapevines and induce wood and foliar symptoms. Grapevine cultivars varied for wood and foliar symptom expression but not for mycelial colonization. However, the severity of foliar symptoms was not related to the rate of spread of the fungus in the grapevine. Furthermore, the staining of wood typically attributed to E. lata did not reflect the presence of the fungus because the fungus was detected up to 80 mm beyond the stain. A field trial with mature grapevines revealed significant differences in the rate of spread of wood staining due to E. lata among eight cultivars, with up to 50 mm/year detected in Cabernet Sauvignon and Shiraz grapevines. In the shadehouse, the maximum growth rate of E. lata was recorded to be 115 mm/year for Grenache rootlings. Information from this study may help to optimize management strategies for maintaining productivity of grapevines with Eutypa dieback, thus reducing the economic impact of the disease.

Hierarchical approach to the assessment of fishing effects on non-target chondrichthyans: case study of Squalus megalops in southeastern Australia

A three-levelled hierarchical risk assessment approach was trialed using piked spurdog (Squalus megalops) to evaluate the suitability of the approach for chondrichthyan species. At level 1, a qualitative assessment indicated that the only fishing-related activity to have moderate or high impact on S. megalops was "capture fishing" by otter trawl, Danish seine, gillnet, and automatic longline methods. At level 2, a semi-quantitative assessment ranked S. megalops at risk because of its low biological productivity and, possibly, its catch susceptibility from cumulative effects across the separate fishing methods. Finally, at level 3, a quantitative assessment showed that population growth is slow even under the assumption of density-dependent compensation where the fishing mortality rate equals the natural mortality rate. Although published information indicates that relative abundance has been stable in several regions of southern Australia, it is concluded that given its low biological productivity, changed fishing practices leading to increased fishing mortality could quickly put S. megalops at high risk. The hierarchical approach appears particularly useful for assessment of chondrichthyan species in data-limited fisheries. This approach allows for a management response at any level, optimizing research and management efforts by identifying and excluding low-risk species from data intensive assessments.

Application of reactive phosphate rock and sulphur fertilisers to enhance the availability of soil phosphate in organic farming

Plant available soil phosphate is frequently deficient for crop and pasture production on organic farms in southern Australia. Improved P management, including developing a fertiliser product conforming to organic farming regulations, is required to sustain and increase production on these farms. Reactive phosphate rock (RPR) and elemental sulphur (S) are natural products. Field and pot experiments were established to measure the impact of ground RPR, and co-treatment of RPR with finely ground S, on available soil phosphate (Olsen P), plant dry matter, and the P concentration (%) and content (kg P ha−1) of the dry matter. Under dry-land field conditions characteristic of cropping regions in southern Australia ( 1,000 mm) and soil organic carbon concentration (OC 11%). It was deduced that the S is probably required to overcome the constraint on dissolution of RPR resulting from frequent periods of low soil moisture. It was concluded that for the south-eastern Australian cropping zone, co-treatment of ground reactive phosphate rock with finely ground elemental S, at ratios (RPR:S) of at least 2:1, depending on soil pH, is required for effective use␣of RPR, even in strongly acidic soil (pHCa < 4.5). It was recommended that ‘organic’ farmers may recover soil P fertility by applying RPR + S fertiliser to the most acidic fields, postponing soil liming, and managing the fields to conserve soil moisture.

Estimates of beneficial and harmful sun exposure times during the year for major Australian population centres

To examine the influence of geographical and seasonal factors on duration of solar ultraviolet (UV) radiation exposure of skin to produce recommended vitamin D levels without producing erythema. An ecological study using daily Ultraviolet Index (UVI) data collected in major population centres across Australia for 1 year (1 January - 31 December 2001) to calculate sun exposure times for recommended vitamin D production and erythema. Sun exposure times to produce either serum vitamin D concentrations equivalent to an oral intake of 200-600 IU/day or erythema for people aged 19-50 years with fair skin (Fitzpatrick type II skin) exposing 15% of the body. In January, across Australia, 2-14 minutes of sun three to four times per week at 12:00 is sufficient to ensure recommended vitamin D production in fair-skinned people with 15% of the body exposed. However, erythema can occur in as little as 8 minutes. By contrast, at 10:00 and 15:00, there is a greater difference between exposure time to produce erythema and that to produce recommended vitamin D levels, thereby reducing the risk of sunburn from overexposure. From October to March, around 10-15 minutes of sun exposure at around 10:00 or 15:00 three to four times per week should be enough for fair-skinned people across Australia to produce recommended vitamin D levels. Longer exposure times are needed from April to September, particularly in southern regions of Australia. Our study reinforces the importance of existing sun protection messages for the summer months throughout Australia. However, fair-skinned people should be able to obtain sufficient vitamin D from short periods of unprotected sun exposure of the face, arms and hands outside of the peak UV period (10:00-15:00) throughout Australia for most of the year. The greater variability in sun exposure times during winter, means that optimal sun exposure advice should be tailored to each location.

Organochlorine and trace metal residues in adult southern bent-wing bat ( Miniopterus schreibersii bassanii) in southeastern Australia

In recent times, the apparent population decline of the southern bent-wing bat ( Miniopterus schreibersii bassanii) at Bat Cave, Naracoorte has been ascribed to pesticide use in the region, following the finding of organochlorine and orgaonophosphate insecticide residues in bat guano. Adult southern bent-wing bats were collected from Bat Cave and Starlight Cave in 2003. Organochlorine contaminants were detected in all carcass samples: p, p′-DDE was by far the most dominant contaminant with concentrations ranging from 11 000 to 59 000 ng g −1, followed by p, p′-DDT (110–1600 ng g −1), p, p′-DDD (35–620 ng g −1), ∑PCBs (33–490 ng g −1), ∑chlordane and related compounds (7.9–270 ng g −1), HCB (1.6–120 ng g −1), HP epox. (3.1–230 ng g −1), TCPMOH (3.8–38 ng g −1), ∑HCHs (1.4–9.6 ng g −1), and TCPMe (0.1–4.2 ng g −1) (all values on lipid-weight basis). No significant difference in DDE, DDD, DDT, ∑DDT, ∑PCB, trans-chlordane, heptachlor epoxide, trans-nonachlor, α-HCH, β-HCH, γ-HCH, TCPMOH or TCPMe concentrations were observed either between sexes within sites, or between sites ( p > 0.05). However, there were significant differences in HCB and oxychlordane concentrations between sexes and between sites ( p < 0.05), between site differences in cis-nonachlor concentrations in male bats ( p < 0.05), and cis-chlordane concentrations between sexes at Starlight Cave, and between males of each site ( p < 0.05). There were also significant differences in the liver concentrations of some metals between sexes within sites (Ag, Cd, Co, Cu, Pb, Se, Zn), and between sites (Ag, Cd, Co, Cu, Hg, Pb, Se, V, Zn). Clustering or grouping of sites was observed when the OC data was expressed on a lipid-weight basis. These inter-site differences in OC concentrations reflect local exposure over a period of time, and do not unambiguously support any suggestion that we are witnessing incipient speciation. However, for conservation purposes, it may be prudent to assume that there are two sub-populations of M. s. bassani feeding in different locations in this region of southern Australia, rather than the single homogeneous population suggested by genetic studies.

Comparative responses of Lolium perenne and Phalaris aquatica to multiple growth stresses

The growth and carbon distribution patterns of perennial ryegrass (Lolium perenne L. cv. Yatsyn1) and phalaris (Phalaris aquatica L. cv. Holdfast) were analysed in response to defoliation and limited nitrogen availability stresses, imposed both individually and in combination. Both species showed similar responses to defoliation and nitrogen limitation when applied individually. Defoliation increased proportional export of carbon from residual leaves and carbon distribution to tillers was increased at the expense of roots. Nitrogen deficiency resulted in increased export of carbon to the root system. These results are consistent with source–sink theory. A key finding from this study was that the species responded differently when defoliation and nitrogen limitation were imposed simultaneously. Under these conditions, carbon distribution patterns in phalaris resembled those seen in plants subjected to nitrogen stress, that is, favouring root growth. The response of perennial ryegrass was to continue to support shoot growth at the expense of roots. These results suggest a physiological basis for the poor survival of perennial ryegrass often observed under continuous grazing in dry regions of southern Australia. Results are discussed in relation to the environments to which each species is adapted, and the management requirements for species persistence in marginal environments.

The influence of behaviour and season on habitat selection by a small mammal

This study examined the selection of habitat by Ningaui yvonneae, a small, nocturnal insectivorous marsupial of semi‐arid regions of southern Australia. In addition to idengifying habitat preferences, the study was concerned with idengifying how habitats were used, and for what purpose they were valued. Triodiairritans (hummock grass) was the most preferred habitat component overall. However, other habitat components were found to be of equal or greater preference during certain seasons and for certain behaviours. The importance of considering behaviour in studies of habitat selection was discussed. Habitat selection by N. yvonneae appeared to be influenced by predation risk and energetic reward. The selection for Triodia is thought to be due to its provision of protection and foraging opportunities. However, leaf litter was preferred over Triodia for foraging, possibly because it offered greater energetic returns. To minimise predation risk while in leaf litter, ningauis remained close to Triodia and moved larger prey items to the edge of Triodia for consumption.

Influence of the Indian Ocean Dipole on the Australian winter rainfall

Using an atmospheric general circulation model and observed datasets of sea surface temperature and rainfall, we studied the influence of the Indian Ocean Dipole (IOD) on the Australian winter rainfall. The IOD has significant negative partial correlations with rainfall over the western and southern regions of Australia. These negative partial correlations extend south‐eastward from Indonesia all the way to south east Australia. Our atmospheric general circulation model sensitivity experiments indicate that cold sea surface temperature anomalies prevailing west of the Indonesian archipelago during the positive IOD events introduce an anomalous anticyclonic circulation at lower levels over the eastern tropical and subtropical Indian Ocean, and over much of the Australian continent. It is also apparent that the response of the atmosphere to the IOD in this region is baroclinic, causing anomalous subsidence and anomalous reduction in the rainfall over the affected regions of Australia.

Compilation of U–Pb zircon data from the Willyama Supergroup, Broken Hill region, Australia: Evidence for three tectonostratigraphic successions and four magmatic events?

The Willyama Supergroup of the Broken Hill region in southern Australia consists of supracrustal sedimentary and magmatic rocks, formed between 1810 and 1600 Ma. A statistical analysis of nearly 2000 SHRIMP U–Pb zircon spot ages, compiled from published and unpublished sources, provides evidence for three distinct tectonostratigraphic successions and four magmatic events during this interval. Succession 1 includes Redan Geophysical Zone gneisses and the lower part of the Thackaringa Group (Cues Formation). These rocks were deposited after 1810 Ma and host granite sills of the first magmatic event (1710–1700 Ma). Succession 2 includes the upper Thackaringa Group (Himalaya Formation), the Broken Hill Group and the Sundown Group and was deposited between 1710 and 1660 Ma. These rocks all contain detrital zircons from the first magmatic event (1710–1700 Ma) and in some cases from the second magmatic event (1690–1680 Ma). The second magmatic event (1690–1680 Ma) was bimodal, resulted from crustal extension, and was coeval with deposition of the Broken Hill Group and deepening of the basin. With this event a mafic sill swarm focused in the Broken Hill Domain. Mafic sills lack any trace of inheritance, unlike the granitoids that commonly contain inherited zircons typical of the supracrustal sediments. Succession 3, the Paragon Group and equivalents were deposited after 1660 Ma, but before a regional metamorphic event at 1600 Ma. Metamorphism was closely followed by inversion of the succession into a fold‐and‐thrust belt, accompanied by a fourth late to post‐orogenic magmatic event (ca 1580 Ma) characterised by granite intrusion and regional acid volcanism (the local equivalents of the Gawler Range Volcanics in South Australia).

Habitat selection by the small dasyurid Ningaui yvonneae (Marsupialia: Dasyuridae) in South Australia

AbstractThis study investigated the habitat preferences of Ningaui yvonneae, a small, nocturnal insectivorous marsupial of the semi‐arid regions of southern Australia. Habitat composition was assessed at both the local (trapping grid) and trap scale. Multiple linear regression revealed a significant positive relationship between captures of N. yvonneae and the abundance of hummock grass (Triodia irritans) at the local scale. At the trap scale, the interaction between Triodia irritans and shrubs was found to be significant. This is thought to reflect the importance of the availability of cover to ningauis. Triodia was an essential component of that, probably because it affords greater protection from predators. This study provides quantitative habitat data that supports the contention of other studies that N. yvonneae has a strong positive association with Triodia spp.

The dynamics and conservation of a spatially subdivided avian population in a fragmented landscape

Many bird species have declined in abundance in the agricultural regions of southern Australia, The mechanisms underlying these declines and the viability of the remaining populations are largely unknown, A number of species exist as spatially subdivided populations in heavily fragmented landscapes. Metapopulation and source-sink theory have influenced thinking on the dynamics of subdivided populations, but the general applicability of these theories is uncertain. I examined the dynamics of a subdivided population of the Rufous Treecreeper Climacteris ruta, a declining woodland passerine, occupying a fragmented, agricultural landscape in southwestern Australia. I determined if local populations could replace themselves without immigration and estimated population growth rates for the periods 1998-1999 and 1999-2000. I also examined the influence of movement between local populations on the viability of the entire subdivided population. Out of four geographically defined local populations, only one was above replacement, and only in one year of the study. Fledgling productivity and recruitment in the remainder were not sufficient to compensate for breeding female mortality. Long-term population growth estimates were &lt;1 for all local populations, but variability in demographic rates suggested that the status of these populations may fluctuate over time. Also, there appeared to be sufficient movement between local populations, and into the study area from nearby habitat remnants, to slow or halt any decline in local population size, Within- and between-local-population processes appeared to be important to the viability of the treecreeper population during the two years of the study, and this is consistent with the general principles of metapopulation theory. I compared the dynamics of the treecreeper population occupying the fragmented landscape with one occupying a continuously wooded landscape and found that the latter had population growth rates &gt;1, suggesting it may be an important population source and vital to the regional viability of the species.

The potential of NIR spectroscopy to predict nitrogen mineralization in rice soils

Prediction of nitrogen (N) mineralization is important for specifying the optimum rate of N fertilizer for flooded rice at the time of sowing. To develop a predictive test, soils (0–0.1 m) were sampled from 22 farms throughout the rice-growing region of southern Australia over a 4-year period. Near infrared reflectance (NIR) spectra of the soils were compared with sixteen biological and chemical soil tests for the prediction of N-uptake by rice plants from these soils in the field and glasshouse. The aim of the study was to develop a soil-NIR calibration as an accurate, rapid and economical mineralization test. Nitrogen uptake by field-grown and glasshouse-grown plants was poorly correlated (r = 0.30), even though significant NIR calibrations were developed with both. Since N uptake by rice in the field was affected by varying weather and management, the field calibration is probably spurious. The calibration of soil NIR spectra with N uptake by glasshouse plants was satisfactory, with a standard error (SE) of 13 kg ha−1 over a range of 11 – 95 kg ha−1, and a correlation between calculated and measured N uptake (r = 0.87, P<0.001). An even better soil-NIR calibration was found with N-mineralization after 21 days of anaerobic incubation (SE 16 mg kg−1, range 52–175 mg kg−1). Analysis of the soil spectra showed that similar wavelengths were correlated with both plant-N uptake and mineralization. NIR spectroscopy shows considerable potential to predict soil N mineralization, and may assist future fertiliser decision support.

Some Observations On Foraging Behaviour In The Southern Ningaui, Ningaui Yvonneae

THE southern ningaui (Ningaui yvonneae) is a small dasyurid inhabiting semi-arid regions of southern Australia. It is a nocturnal predator, feeding mainly on small invertebrates (Woolnough and Carthew 1996; Fisher and Dickman 1993). During a larger research project examining population dynamics. habitat selection and diet, I observed and documented aspects of the foraging behaviour of N. yvonneae. These observations, which are difficult to quantify, provide insight into the ecology of this poorly studied species.

Leaching and degradation of triasulfuron, metsulfuron-methyl, and chlorsulfuron in alkaline soil profiles under field conditions

A field study was conducted on an alkaline cropping soil (plot size 4 m by 1 m), representative of cereal growing regions in southern Australia, to examine the degradation and leaching behaviour of triasulfuron, metsulfuron-methyl, and chlorsulfuron (150 g a.i./ha), along with a non-reactive tracer (KBr, 50 kg/ha), under 2 water treatments (‘rainfall’ and ‘rainfall + irrigation’). The results showed that the distributions of water content, Br– , and the 3 herbicides were influenced by the amount of rainfall/irrigation received, and the biological activity as well as the physico-chemical properties of the soil within the profile. The largest concentrations of Br– were detected in the 10–20 cm depth under both treatments. No additional peak of Br– was observed in the plots which received only rainfall; however, there was another peak at 100 cm depth after a cumulative rainfall and irrigation of 158 mm. The spatial distribution of Br– in the plots was attributed to preferential flow through cracks or the presence of ‘mobile’ and ‘immobile’ water, which gave rise to bimodal distribution in the profile. Metsulfuron-methyl showed the greatest mobility, followed by chlorsulfuron and triasulfuron under both the treatments, with metsulfuron-methyl being detected at 120 cm depth under rainfall + irrigation. A bimodal distribution was also observed for the 3 herbicides, but the location of peaks was dependent on the solute. Rates of degradation of the herbicides could be described reasonably well with first-order reaction kinetics (r2 = 0.72–0.91). The half-lives for triasulfuron, metsulfuron-methyl, and chlorsulfuron were 44, 45, and 32 days, respectively, under rainfall (69 mm), and 46, 59, and 48 days under rainfall + irrigation (158 mm).

Rate of increase as a function of rainfall for house mouse Mus domesticus populations in a cereal‐growing region in southern Australia

Summary 1. Mouse plagues are a significant problem to agricultural areas of Australia, causing millions of dollars of damage. This study was conducted to determine if rainfall could explain the occurrence of mouse plagues. 2. On average, data on mouse abundance were collected every month, using mark‐release‐recapture techniques, from the Victorian Mallee cereal‐growing region, from February 1983 to October 1994. No data were collected from December 1990 to September 1992. Three plagues of mice occurred during these 12 years. We examined the rate of increase of mouse populations as a function of antecedent rainfall. 3. The highest observed rate of increase per month was during 1986 (r = 1·86). The highest observed rate of decrease per month was during 1984 (r = –2·85). The maximum rate of increase of mouse populations used in the numerical response function was 1·16 month–1. The best estimate for the numerical response function was robs = –6·79 + 7·95 (1 – e–1·11V). 4. The numerical response of mouse populations to rainfall was examined against 6‐month accumulated rainfall that was lagged by 0, 3 and 6 months. The best fit of the model was to lag rainfall by 3 months. 5. Two systems for the response of mouse populations to rainfall are described. The plague system occurred when mouse populations responded to rainfall: populations increased following high rainfall and decreased following low rainfall. The non‐plague system occurred when the exponential rate of increase and rainfall were independent: populations crashed after a plague and were unable to respond to rainfall for at least 2 years thereafter. 6. The two systems suggest that there is ‘biological memory’ that masks the effect of rainfall for a minimum period after a mouse plague. This memory appears to be associated with the time since the last plague, the population response by mice (including shifts in age structure) in the previous year, and the abundance of mice after the spring decline. If rainfall is used to predict mouse plagues to assist in their management, the biology of the system must be known.

Habitat of the Regent Honeyeater Xanthomyza phrygia and the value of the Bundarra-Barraba region for the conservation of avifauna

Five types of woodland and forest in the Bundarra-Barraba region of northern New South Wales were surveyed for Regent Honeyeaters Xanthomyza phrygia and other birds over two years. Regent Honeyeaters were found in 24 of the 93 transects, at a density of 0.09 birds/ha. Most were found in box-ironbark woodland (34% of 62 sites), with single records from box-gum woodland, box-stringybark woodland and dry plateau complex woodland. No Regent Honeyeaters were found in riparian gallery forest during censuses, but they were found breeding there at other times. All habitats contained a high density of birds, compared to other wooded regions in southern Australia, with riparian gallery forest and box-ironbark woodland being particularly rich in species and numbers. These habitats had greater flowering indices, larger trees and more mistletoes than other habitats. Sites used by Regent Honeyeaters supported significantly more birds and bird species than unoccupied sites. The region supports a total of 193 species, four of which are nationally threatened and seven which are threatened in New South Wales. The richness of the bird community in the region is partly because it retains a higher proportion of native vegetation cover (43%) than many other parts of rural Australia. Protection and rehabilitation of box-ironbark woodland and riparian gallery forest is of high priority in a regional conservation plan. However, all habitats in the Bundarra-Barraba region should be protected from clearing and degradation, because they are also used at times by Regent Honeyeaters and support a wide range of bird species. Wise management should retain many sensitive bird species that have disappeared from or declined in other regions of southeastern Australia.

Increased Soil Salinity Causes Elevated Cadmium Concentrations in Field-Grown Potato Tubers.

Elevated Cd concentrations have been observed in potato (Solatium tuberosum L.) tubers from commercial crops in certain regions of southern Australia. Reasons for enhanced Cd uptake by tubers were investigated by a survey of commercial crops and associated soils. Eighty-nine sites were selected and paired tuber and soil samples taken. Concentration of Cd in tubers was compared to potato variety, tuber elemental composition, and chemical-physical characteristics of topsoil (0-150) and subsoil (150-300 mm). Tuber Cd concentrations were positively related to soil electrical conductivity (EC) and extractable Cl (R2 = 0.62, P < 0.001) in the topsoil, with extractable Cl accounting for more variation than EC. Tuber Cd concentrations were not strongly related (R2 = 0.23, P < 0.05) to potato variety alone. However, inclusion of variety and EDTA-extractable Zn with water-extractable Cl in a multivariate model resulted in a small but significant improvement in the variance accounted for by the model (R2 =0.73, P < 0.001). Tuber Cd was unrelated to tuber concentrations of P or S, but was positively related to concentrations of major cations in the tuber, particularly Na. Soil pH, total C, EDTA-extractable Cd, or particle-size distribution were not correlated to tuber Cd concentrations, either singly or after inclusion in a multivariate model with soil Cl concentrations. As Cl is known to mobilize soil Cd and increase its phytoavailability, elevated Cd concentrations in potato tubers in southern Australia appear to be largely a result of the use of saline irrigation waters.

Distribution in Australia and host plant specificity of Phomopsis emicis, a stem blight pathogen of Emex australis

The stem blight pathogen, Phomopsis emicis, is widespread on Emex australis throughout those regions of southern Australia with a Mediterranean climate. Host specificity tests showed that P. emicis was able to cause leaf lesions or stem collapse on five closely related species, E. australis, E. spinosa, Rumex alcockii, R. dumosus and R. pulcher, in the Polygonaceae. Two of these species, R. alcockii and R. dumosus, are native to Australia and the others are introduced weeds. P. emicis was able to colonize the wounded or senescent tissue of several other plant species, thereby demonstrating its facultative saprophytic ability. There was evidence that P. emicis was able to survive as an endophyte in Muehlenbeckia adpressa and Polygonum aviculare.

National survey of viruses in pastures of subterranean clover. I. Incidence of four viruses assessed by ELISA

A nationwide survey was made of the time-course incidence of alfalfa mosaic virus (AMV), clover yellow vein virus (CYVV), subterranean clover mottle virus (SCMoV) and subterranean clover red leaf virus (SCRLV) in improved pastures in southern regions of Australia over a 3-year period. Up to 2 500 samples (cvv. Mt Barker or Woogenellup) were collected in winter and spring of 1984, 1985 and 1986 in each of New South Wales, Victoria, South Australia. Western Australia and Tasmania, and assayed by ELISA. Usually, each sample consisted of one or two plants or parts thereof. However, a small number of samples in winter contained parts of up to 10 seedlings. For this reason, incidences are expressed as percentage of infected samples rather than percentages of infected plants. All four viruses occurred in all five states. Averaged over all states, the incidence of infected samples increased progressively from 15.3 to 19.9 to 22.5% from 1984 to 1985 to 1986, respectively, in spring, and from 6.8 to 13.8 to 18.8% respectively in winter. The incidence of samples infected with multiple infections (2-4 viruses) increased from 1.9 to 3.2 to 5.0% from 1984 to 1985 to 1986, respectively, in spring, and from 0.5 to 1.6 to 4.0%, respectively, in winter. Since 1-4 viruses were detected in each infected sample, more individual infections than infected samples were recorded. For example, the incidence of virus infections per paddock increased progressively from 17.5 to 24.1 to 28.6% from 1984 to 1985 to 1986, respectively, in spring. On a state basis, the incidence of infected samples was greatest in W.A., reaching 38.9 and 34.9% in spring of 1985 and 1986, respectively, and in S.A. reaching 30.3% in spring of 1986; these high levels were due largely to SCMoV which reached 97% in one paddock in each of the two states. In N.S.W., Vic. and Tas., the highest incidences of infected samples in either winter or spring were 21.4, 16.2 and 23.1%, respectively. Averaged over all states, the highest mean incidence recorded for samples infected with individual viruses in either winter or spring was 9.4% for AMV, 5.7% for CYW, 10.9% for SCMoV and 7.5% for SCRLV. For AMV and SCRLV, there was an increasing trend from spring 1984 to spring 1986. A similar increasing trend for SCMoV was more evident in winter than in spring. For CYVV, no time-course pattern was evident. These results support the proposition that viruses contribute significantly to 'clover-decline', a well-known problem in pastures of subterranean clover.

National survey of viruses in pastures of subterranean clover. II. Statistical methodology for large scale quantitative ELISA

Statistical methodology was applied to a survey of time-course incidence of four viruses (alfalfa mosaic virus, clover yellow vein virus, subterranean clover mottle virus and subterranean clover red leaf virus) in improved pastures in southern regions of Australia, with samplings in each winter and spring over 3 years. The 100 samples per paddock collected at each time of sampling provided detection probabilities of 0.63 and 0.87 for 1% and 2% infection respectively. A microtitre plate design for ELISA was developed to include 60 field samples, 10 glasshouse-grown healthy control samples and 6 glasshouse-grown samples infected with the virus under examination. This design was used on 816 plates for each of the four viruses tested. The method used for identification of virus in sap of a plant sample from a particular paddock was that the ELISA reading was both significantly greater than healthy control readings, and an outlier in the distribution of readings of all sap samples from that paddock. It is argued that as the identification of uninfected samples as infected was highly unlikely, this double criterion method was superior to the use of each criterion separately. Use of significance above healthy control values as the sole criterion would have increased virus incidences by about 60%; use of outlier identification as the sole criterion would have increased virus incidences by about 30%. A generalized linear model with binomial errors and logit link was used for adjusting the virus incidences reported in the previous paper (Helms et al. 1993) for biases due to paddocks and/or districts not sampled on some occasions. This adjustment slightly increased overall incidences in all but one sampling and confirmed the time-course increase in incidence over the 3 years of the survey. The same model also proved to be the most appropriate for investigating the effects of year, season and district on virus incidence.