bluuebunny/crossref_metadata_2025 huggingface dataset:
Response to divergent selection for early vigour in sunflower (Helianthus annuus L.)
Authors: Agüera F. , Villalobos F. J. , Orgaz F. , Fernandez-Martinez J. M.
Published: August 2004

Early vigour (EV), biomass at the first development stages, may be a positive
trait to improve sunflower yield in water-limited environments. Field
experiments were carried out from 1992 to 1995 to define an index to quantify
EV in sunflower plants, evaluate the response to divergent selection for this
trait, study EV ×environment interaction, estimate the heritability of
EV, and study the association of EV with other traits. A sunflower population
with a broad genetic base and 10 sunflower lines derived from it were used.
Stem volume calculated from stem diameter and height measured approximately
425 degree-days after emergence was correlated with above-ground plant biomass
at the same date. In 1992, divergent selection for high and low stem volume
was carried out on this population and plants from every group were recombined
independently, obtaining 2 new populations. Selection response, using these
and the initial population, was studied in 1993. Ten S2 lines, 5 with high-EV
derived from the high-EV population and 5 with low-EV derived from the low EV
population, were sown in 1995 to study the EV ×environment interaction.
Differences among lines with different EV were significant in all the
environments studied. In 1993, a random sample from the initial population was
selfed and broad sense heritability and heritability by parent-offspring
regression were estimated. Heritability based on variance component estimates
of S1 progeny means was 0·61. Realised
heritability (± s.e.) from a divergent selection for high and low stem
volume were 0·40±0·10 and 0·52±0·15,
respectively. Heritability by parent-offspring regression was 0·
40± 0·10. These values and the high variability of stem volume
observed in the new populations indicate that additional gain from selection
should be possible.
The source of mineral nitrogen for cereals in south-eastern Australia
Authors: Angus J. F. , van Herwaarden A. F. , Heenan D. P. , Fischer R. A. , Howe G. N.
Published: August 2004

The relative importance of soil mineral nitrogen (N) available at the time of
sowing ormineralised during the growing season was investigated for 6 crops of
dryland wheat. The soil mineral N in the root-zone was sampled at sowing and
maturity and the rate of net mineralisation in the top 10 cm was estimated by
sequential sampling throughout the growing season, using an in situ method.
Mineralisation during crop growth was modelled in relation to total soil N,
ambient temperature, andsoil water content.
Mineral N accumulated before sowing varied by a factor of 3 between the sites
(from 67 to 195 kgN/ha), while the net mineralisation during crop growth
varied by a factor of 2 (from 43 to 99 kgN/ha). The model indicated that
0·092% of total N was mineralised per day when temperature and
water were not limiting, with rates decreasing for lower temperatures and soil
water contents. When tested with independent data, the model predicted the
mineralisation rate of soil growing continuous wheat crops but underestimated
mineralisation of soil in a clover-wheat rotation. For crops yielding <3
t/ha, the supply of N was mostly from mineralisation during crop growth
and the contribution from mineral N accumulated before sowing was relatively
small. For crops yielding >4 t/ha, thesupply of N was mostly from N
present in the soil at the time of sowing. The implication is that for crops
to achieve their water-limited yield, they must be supplied with an amount of
N greater than can be expected from mineralisation during the growing season,
either from fertiliser or from mineral N accumulated earlier.
Wool growth and fibre diameter changes in young Merino sheep genetically different in staple strength and fed different levels of nutrition
Authors: Thompson A. N. , Hynd P. I.
Published: August 2004

The wool growth response to nutrition by Merino weaners (liveweight 33·
2±0·58 kg) bred for high or low staple strength (SS) and fed to
produce changes in liveweight was examined. The hypothesis tested was that
genetic differences in SS are associated with differences in along-fibre
variation in diameter. Sheep fed to maintain liveweight produced wool at a
more constant rate with smaller and less rapid changes in fibre diameter than
that produced by sheep which lost and then gained liveweight
(P < 0·001). There were significant
(P < 0·05) but relatively small differences in
wool growth rate and fibre diameter between the SS selection flocks, and wool
from sheep selected for high SS had less (P < 0
·001) variation in diameter between individual fibres than wool from
sheep selected for low SS
Minimum fibre diameter was most closely associated with SS, accounting for
66% (P < 0·001) of the total variance
in SS generated by selective breeding and nutrition. An increase in minimum
fibre diameter of 1µm was associated with an increase in SS of about 5
N/ktex. Minimum fibre diameter and the rate of change in fibre diameter to
the point of break along the staple collectively accounted for 72%
(P < 0·001) of the total variance in SS.
Addition of a term for between-fibre variation in diameter measured at the
point of break removed an additional 8% (P <
0·001) of the variance in SS. We conclude that the mechanisms
responsible for nutritionally induced and genetic differences in SS are not
the same. Nutrition influences SS by affecting along-fibre diameter changes,
whereas genetic differences in SS, at least as far as they are represented by
the flocks used here, are largely attributable to between-fibre variations in
diameter. The independence of nutritional and genetic effects on SS means that
they should be exploited concurrently to reduce the incidence of tender wool
production.
Influence of applied nitrogen on vegetative, reproductive, and aerial tiller densities in Lolium perenne L. during the establishment year
Authors: McKenzie F. R.
Published: August 2004

The influence of applied nitrogen (N) (120-720 kg/ha · year) on
Lolium perenne (perennial ryegrass) vegetative,
reproductive, and aerial tiller densities was monitored during the
establishment year under grazing. Total (vegetative, reproductive, and aerial)
tiller densities ranged from 3500 tillers/m2 (at 120
kg N/ha · year) during April 1994 to 17 800
tillers/m2 (at 600 kg N/ha · year) during
August 1994. Increasing levels of N (up to 360 kg N/ha · year)
increased total tiller density. Reproductive tillers were observed in November
and December 1993 and ranged from 6 (at 600 kg N/ha · year) to 27
(at 480 kg N/ha · year) tillers/m2.
Nitrogen levels above 240 kg/ha · year promoted reproductive tiller
development, whereas levels above 600 kg/ha · year depressed
reproductive tiller development. Since the low reproductive tiller densities
resulted from frequent intensive grazing, little practical importance can be
attached to these results. Aerial tiller densities ranged from 12 (at 480 kg
N/ha · year) in January to 487 (at 720 kg N/ha · year)
tillers/m2 in September 1994. Increasing levels of
applied N increased aerial tiller density, whereas at low levels (120 and 240
kg N/ha · year) aerial tillering was negligible.
Genetics and race variability of the lucerne-Colletotrichum trifolii pathosystem in Australia
Authors: Mackie J. M. , Irwin J. A. G.
Published: August 2004

The Australian-bred lucerne cultivars, Trifecta and Sequel, were found to
possess useful levels of resistance to both
Colletotrichum trifolii races 1 and 2. Race 2 has only
been previously observed in the United States and surveys did not reveal its
presence in Australia. Multilocus finger printing using random amplified
polymorphic DNA (RAPDs) analysis revealed low diversity (<10%
dissimilarity) within Australian C. trifolii collections, and between the Australian race 1
isolates and a US race 2 isolate. Studies on the inheritance of resistance to
C. trifolii race 1 in individual
clones from Trifecta and Sequel revealed the presence of 2 different genetic
mechanisms. One inheritance was for resistance as a recessive trait, and the
other indicated that resistance was dominant. The recessive system has never
been previously reported, whereas in the US, 2 completely dominant and
independent tetrasomic genes An1 and
An2 have been reported to condition
C. trifolii resistance. It was not
possible to fit the observed segregations from our studies to a single-gene
model.
In contrast to US studies, clones of cv. Sequel exhibiting the recessive
resistance reacted differently to spray and stem injection with
C. trifolii inoculum, being
resistant to the former and susceptible to the latter, providing additional
evidence for the presence of a different genetic mechanism conditioning
resistance to those previously reported in the US. As C. trifolii is one of the most serious diseases of lucerne
worldwide, the future development of molecular markers closely linked to the
dominant and recessive resistances identified in these studies, and the
relationships between these resistances and An1 and
An2 as determined by genetic mapping, appear to be
useful areas of future study.
Nitrogen and water flows under pasture - wheat and lupin - wheat rotations in deep sands in Western Australia. 2. Drainage and nitrate leaching
Authors: Anderson G. C. , Fillery I. R. P. , Dunin F. X. , Dolling P. J. , Asseng S.
Published: August 2004

Quantification of nitrate (NO-3)
leaching is fundamental to understanding the efficiency with which plants use
soil-derived nitrogen (N). A deep sand located in the northern wheatbelt of
Western Australia was maintained under a lupin
(Lupinus angustifolius)-wheat
(Triticum aestivum) and a subterranean clover
(Trifolium subterraneum) based annual pasture-wheat
rotation from 1994to 1996. Fluxes of water and
NO-3 through, and beyond, the
root-zone were examined. Drainage was calculated on a daily basis from
measurements of rainfall, evapotranspiration, and the change in soil water
content to a depth of 1·5 m. Evapotranspiration was estimated from
Bowen ratio measurements,and soil water content was determined by time domain
reflectrometry. Soil was sampled in layers to1·5 m at the onset of
winter rains and analysed for NO-3
. Ceramic suction cups were installed at 0·25, 0·4, 0·6,
0·8, 1·0, 1·2, and 1·4 m to sample soil solution
from June to mid August. The NO-3
leached from each layer was computed by multiplying the daily drainage through
each layer by the estimated concentration of
NO-3 within the layer. The
estimated concentration of NO-3 in
a layer was calculated by taking into account
NO-3 either entering that layer
through mineralisation and leachingor leaving the layer through plant uptake.
Mineral N was added to the surface 0·2 m in accordance with measured
rates of net N mineralisation, and daily N uptake was calculated from the
measured above-ground plant N derived from soil N. Root sampling was
undertaken to determine root lengthdensity under pastures, lupin, and wheat.
Cumulative drainage below 1·5 m was similar under wheat and lupin, and
accounted for 214 mmfrom 11 May to 15 August 1995 and 114 mm from 2 July to 15
September 1996. The cumulative evapotranspiration (Ea)
over these periods was 169 mm from a wheat crop in 1995, and 178 mm from a
lupin crop in 1996. The amount of
NO-3 in soil at the start of the
growing season was afiected by previous crop, with a lower range following
wheat (31-68 kg N/ha) than following legumes (40-106 kgN/ha). These
large quantities of NO-3 in the
soil at the break of the season contributed substantially to
NO-3 leaching. Leaching of
NO-3 below 1·5 m in wheat
crops accounted for 40-59 kg N/ha where these followed either lupin or
pasture. In contrast, less NO-3
was found to leach below 1·5 m in pastures (17-28 kg N/ha). Greater
N uptake by capeweed (Arctotheca calendula L.) than by either wheat or lupin
was the main reason for the lower amount of
NO-3 leached in pastures.
Variation in yield of narrow-leafed lupin caused by terminal drought
Authors: Dracup Miles , Reader Mark A. , Palta Jairo A.
Published: August 2004

Narrow-leafed lupin is a rain-fed crop in southern Australia whose yields are
limited by the amount and distribution of rainfall. Drought terminates the
growing season, and the timing and intensity of development of this
(terminal) drought is a likely cause of much yield
variability. We investigated this yield variability by manipulating terminal
drought with trickle irrigation. Despite comparatively high crop dry mass of
nearly 9 t/ha in the absence of irrigation, seed yield was only 1·2
t/ha with a harvest index of only 14%. Delaying the terminal
drought and thus prolonging the period for crop ripening raised crop dry mass
by 18-42%, with large increases in harvest index and seed yields, which
rose by 45-75% and 95-135%, respectively.
Pod set started 110 days after sowing (DAS) but appreciable pod filling did
not start until 140 DAS, by which time, in the unirrigated treatment, only
about 15% of the plant-available soil water remained, leaf diffusive
conductance had fallen by 75%, and leaf water potential was -1·7
MPa. Leaf senescence and abscission had already begun; in the control
treatment only 25% of the green area remained at 150 DAS, when net
vegetative growth ceased and appreciable seed filling began. During
irrigation, plant-available soil water was maintained at 35-70% of that
at field capacity, with correspondingly better plant water relations. Pod and
seed filling started at the same times as in the unirrigated control, and
vegetative growth ceased at the same time. However, green area declined more
slowly and reproductive growth continued for longer and at a faster rate.
Yields were highly correlated with the number of productive pods (and seeds)
at maturity, which in turn was associated with pod survival rather than pod
set. Irrigation increased the number of surviving pods and seeds, both of
which sometimes aborted at comparatively late stages of filling. Average seed
weights were stable across treatments, except where there was a period of
drought before irrigation, in which case seeds were heavier, compensating for
prior loss of pods.
It is argued that a better ideotype for the Mediterranean environment of
southern Australia would switch to reproductive growth earlier, before severe
water deficit develops, and with less overlap between vegetative and
reproductive growth.
The geographical distribution of the Queensland fruit fly, Bactrocera (Dacus) tryoni, in relation to climate
Authors: Sutherst Robert W. , Yonow Tania
Published: August 2004

CLIMEX is used to analyse the potential distribution of the Queensland fruit
fly in relation to long-term average meteorological data. Different hypotheses
on the mechanisms limiting the distribution of this species are examined. The
analyses indicate that different CLIMEX models discriminate between locations
in different ways. In particular, the models describing the limiting effects
of cold stress yield substantially different estimates of the areas that can
support overwintering populations. With the threshold temperature model of
cold stress, extreme low temperatures exclude flies from high-altitude areas,
but fail to exclude them from areas known not to support overwintering
populations. These areas can only be rendered unfavourable by using the
degree-day model of cold stress, which prevents sufficient thermal
accumulation above the developmental threshold to maintain basic metabolic
processes for long periods. In contrast, 2 models describing different modes
of heat stress accumulation provide similar results and are interchangeable.
Our analyses also indicate the potential for agricultural practices, such as
irrigation, to alter quite dramatically the suitability of an area for
Queensland fruit fly, and impact upon its geographical distribution and the
pattern of activity.
Transpiration effciency and its relationship with carbon isotope discrimination under well-watered and water-stressed conditions in Stylosanthes scabra
Authors: Thumma Bala R. , Naidu Bodapati P. , Cameron Don F. , Bahnisch Len M.
Published: August 2004

Stylosanthes scabra cv. Seca is a widely sown tropical
pasture legume in northern Australia and has a high degree of drought
resistance. Identification of traits contributing to the drought resistance of
Seca may be valuable for use in breeding programs. Transpiration efficiency
(TE) has been suggested as one such trait contributing to drought resistance.
Carbon isotope discrimination (Δ) has been proposed for estimating TE
indirectly in C3 plants. A glasshouse experiment was
conducted using 8 accessions of S. scabra to identify whether Seca differs in
TE from other accessions of S. scabra and to determine the relationship
between TE and Δ under both well-watered and water-stressed treatments.
Seca maintained the highest TE (lowest Δ) under both control and stress
treatments, and leaf Δ was significantly and negatively correlated with
TE under both control and stress conditions. A significant and negative
relationship was found between Δ and dry matter production under stress
treatment. The interaction between accession and watering treatment was not
significant for either TE or Δ. We also found a signirficant agreement
between the performance in the field and in the laboratory for these 8
accessions. These results indicate that TE could be one of the significant
factors contributing to drought resistance of Seca. Furthermore, Δ
and/or specific leaf area may be useful as selection criteria in breeding
programs to identify the lines with high TE.
Effects of a period of high temperature during grain filling on the grain growth characteristics and malting quality of three Australian malting barleys
Authors: Wallwork M. A. B. , Logue S. J. , MacLeod L. C. , Jenner C. F.
Published: August 2004

Short periods of high temperatures (up to 35°C) during mid grain filling
appear to reduce yield and quality in barley. Plants of 3 malting barley
varieties, Schooner, Arapiles, and Sloop (a new South Australian malting
variety), were grown under constant environment conditions from germination to
maturity and exposed to 5 days of high temperatures (up to 35°C) during
mid grain filling. Schooner and Sloop showed similar patterns of accumulation
of dry matter under control conditions (21°C/16°C, day/night
temperature) and in response to high temperatures. In all varieties, the
reduction in starch accumulation represented the most significant detrimental
effect of high temperature and made the greatest contribution to the reduction
in final grain weight. The reduction in absolute grain nitrogen (N) in
heat-treated Arapiles grains represents a potentially important response under
high temperature conditions.
In this study, water loss did not have a decisive role in the termination of
grain filling. Continued accumulation of endosperm dry matter at low moisture
levels suggested that water distribution and/or components of water
potential may be more important than overall water content in the cessation of
grain filling.
Final grain composition depended not only on the amount of endosperm storage
component present in the grain but also on the contribution of the
non-endosperm components (including the embryo and husk) to final grain dry
weight. In some cases, changes in the contribution made by the non-endosperm
components of the grain to final grain weight masked important high
temperature effects on key endosperm storage components.
Hot water extract (HWE) values were similar within treatments and ranged from
73% to 78%. High temperature exposure reduced HWE for all
varieties. Malt b-glucan was lower in heat-treated grains than in control
grains. Despite relatively high malt protein levels in all varieties, higher
free amino N levels in heat-treated grains indicated a higher protein
modification than in control grains.
Effect of on-farm and pre-slaughter handling of pigs on meat quality
Authors: D'Souza D. N. , Leury B. J. , Dunshea F. R. , Warner R. D.
Published: August 2004

Thirty-six crossbred (Large White × Landrace) boars were used to
investigate the effect of positive and negative handling of pigs on-farm over
a period of 5 weeks, and the effect of minimal and negative handling just
prior to slaughter at the abattoir on the level of stress and meat quality of
the carcass. There was no significant difference in adrenal gland weight and
plasma cortisol concentration measured at slaughter between pigs negatively
and positively handled on-farm. Pigs negatively handled on-farm had lower
muscle glycogen 5 min and 40 min post slaughter in the
Longissimus thoracis (LT) but muscle paleness and
percentage drip loss of the LT were similar compared with pigs positively
handled on-farm. Pigs negatively handled at the abattoir had lower muscle
glycogen 5 min post slaughter in the LT; however, muscle paleness, percentage
drip loss, ultimate pH, and incidence of pale, soft, exudative meat were
similar compared with pigs that were minimally handled at the abattoir. This
study has shown how the interaction between pigs and humans on-farm can
influence the pig’s ‘stress’ response to pre-slaughter
handling and, potentially, meat quality.
Sorghum hybrid differences in grain yield and nitrogen concentration under low soil nitrogen availability. I. Hybrids with similar phenology
Authors: Kamoshita A. , Muchow R. C. , Cooper M. , Fukai S.
Published: August 2004

In Australia, grain sorghum [Sorghum bicolor (L.)
Moench] hybrids are often grown under conditions of low soil nitrogen (N)
availability with suboptimal levels of N fertiliser supplied. However, little
is known about the traits that contribute to sorghum hybrid performance in
environments with low available N. We examined plant traits that may
contribute to adaptation of sorghum to low soil N conditions, and the
influence of genotype × N environment interactions on yield and grain N
concentration. Two experiments were conducted using 3–6 hybrids with
similar phenology. Three N fertiliser application rates (0, 60, and 240
kg/ha) were used in Expt 1, and 2 application rates (0 and 60 kg/ha)
were used in Expt 2. Hybrid yield was associated with plant N content at
maturity. The ability of a hybrid to take up N continuously during grain
filling, under N limiting conditions, was identified as an important component
contributing to high yield. In the non-fertilised treatment of Expt 2, where
plants suffered the most severe N limitation before anthesis (e.g. total plant
N content at anthesis <3 g/m2), hybrid yield was
associated with biomass production and duration of effective grain filling.
The dependence of the expression of the higher N uptake trait on N
availability and other environmental factors resulted in genotype ×
environment interactions for yield. Differences among hybrids in leaf
senescence and grain growth rate had little effect on yield.
Genotypic variation for grain N concentration was consistent across
experiments for hybrids with and without the staygreen attribute. In Expt 2
the magnitude of leaf senescence and amount of N mobilised from leaf to grain
were greater at 60 kg N/ha than in the non-fertilised treatment. In
addition, the staygreen hybrid 72389–1-1–3/QL36 had a slower
rate of leaf senescence, took up larger amounts of N after anthesis, and had
higher grain N concentration (1·07%) than the senescent hybrids
ATx623/RTx430 (0·95%) and QL41/69264–2-2–2
(0·90%).
Segregation of glutenins in wheat × maize-derived doubled haploid wheat populations
Authors: Kammholz Stephen J. , Grams Raechelle A. , Banks Phillip M. , Sutherland Mark W.
Published: August 2004

The segregation of both high and low molecular weight glutenin subunits across
7 F1 wheat (Triticum aestivum L.)
× maize (Zea mays L.) derived doubled haploid
populations was examined. The F1 wheats used in each
population were produced from parents of interest to Australian wheat breeding
programs. The parents varied by up to 5 glutenin subunit loci. Examination of
subunits individually within each population using a chi-square analysis
revealed that all but 2 of the 26 pairs of alleles analysed fitted the
expected 1 : 1 segregation ratio. Glutenin profiles were examined for each
cross individually and all but one (Sonalika/Hartog) fitted the expected
Mendelian segregation pattern. The analysis of allele distribution of the 6
glutenin loci across all 7 crosses showed all falling well within expected
segregation ratios. Closer examination of parental lines and populations
revealed irregularities which conflict with original assumptions and provide a
valid explanation for the few segregation distortions observed. It is
concluded that wheat × maize-derived doubled haploid populations
represent a unbiased assortment of parental gametes on both arms of Group 1
chromosomes.
The taxonomy of Colletotrichum isolates associated with lupin anthracnose
Authors: Yang H. A. , Sweetingham M. W.
Published: August 2004

Forty-three Colletotrichum isolates fromLupinus species worldwide are delineated into 3 groups:vegetative compatibility group (VCG)-1 (4 isolates), VCG-2 (37 isolates), andCOL-3 (2 isolates). The 3 groups are readily distinguishable by randomamplified polymorphic DNA (RAPD) profiles. All Australian lupin isolates areVCG-2. VCG-1 and VCG-2 isolates produce predominantly cylindrical conidia, hadregular colony margins, and were grey to brown, lacking pinkish pigmentationon potato dextrose agar (PDA) consistent with the taxonomic criteria forColletotrichum gloeosporioides. COL-3 isolates producepredominantly fusiform conidia, and had an irregular colony margin and apinkish pigmentation on PDA consistent with C. acutatum.COL-3 isolates are possibly strawberry pathogens which can cross-infectlupins. An examination of reference cultures ofC. gloeosporioides and C. acutatumfound that published ‘species specific primer’ polymerase chainreaction (PCR) tests based on ITS sequence homology produced results contraryto the traditional taxonomy based on morphology. RAPD analysis appears todetect greater genetic variation in Colletotrichumisolates than previously published ITS1 sequence homology data, which does notsupport moving lupin anthracnose pathogens VCG-1 and VCG-2 fromC. gloeosporioides intoC. acutatum.Additional key words: Colletotrichum gloeosporioides,Colletotrichum acutatum, Lupinus,vegetative compatibility, RAPD analysis.
The Influence of the Ca2+/K+ Balance and Light Energy on Alkaloid Content and Parttioning in Datura stramonium
Authors: Demeyer K. , Dejaegere R.
Published: August 2004

The influence of a varying
Ca2+/K+ balance on alkaloid
production and accumulation in
Datura stramonium var. tatula L. Torr. (thorn-apple) was
examined. Plants were grown in culture on two different mineral media, that
varied only in the proportions of the two cations. In addition, plants were
cultured under two different light regimes to investigate a possible
interaction between different ecophysiological parameters. When plants were
grown under a higher light energy regime, more alkaloids accumulated in the
plants during a certain stage of development, but also a higher proportion was
found in fruits and seeds. This was associated with a lower alkaloid content
in leaves and stems. The observed effect of the
Ca2+/K+ balance on alkaloid
content in the leaves, was affected by the different light regimes. An
interpretation, including the possible influence on glutamine content, is put
forward.
Distribution of Armillaria luteobubalina and its Impact on Community Diversity and Structure in Eucalyptus wandoo Woodland of Southern Western Australia
Authors: Shearer B. L. , Byrne A. , Dillon M. , Buehrig R.
Published: August 2004

Armillaria luteobubalina Watling & Kile is causinghigh mortality in Eucalyptus wandoo Blakely woodland that receives low annual rainfall of 500–700 mm, and it is a significantdisturbance agent affecting community structure. Discrete disease centresranged from 0.01 ha to 8 ha in size (mean 1.2 ± s.e. 0.3 ha) and had adiscontinuous distribution within the woodland. For 38 disease centres, thetotal area infested was 46.25 ha. Infection caused death of overstorey polesand veterans creating disease centres of greatly reduced biomass. Thisreduction was reflected by a negative correlation between the mortality ofoverstorey and basal area and diameter at breast height over bark (DBH). Theaverage mortality of E. wandoo trees was 47% indisease centres of intermediate impact, compared with 66% for highimpact areas. Regeneration of the host species increased following diseaseexpression, as evidenced by: significantly greater understocking oflignotubers and saplings in disease centres than in non-infested woodland,less bare ground in disease centres than in non-infested woodland, and apositive correlation between the mortality of overstorey and live understorey.By contrast, plant species richness and diversity did not differ significantlybetween infested and non-infested woodland. The severity ofA. luteobubalina infection was not strongly related tosite factors. The rate of disease extension varied considerably between yearsduring the period 1986–1994 and averaged 2.04 ± s.e. 1.05 myr-1. Of the 26 host species recorded, 23% werefrom the Proteaceae followed by a smaller percentage from the Myrtaceae andPapilionaceae (15% each). The high impact ofA. luteobubalina in E. wandoowoodland reflects the high susceptibility of the dominant host to infectionand survival strategies of the pathogen population in the harsh woodlandenvironment.
Seasonal Variation in Water Relations of Trees of Differing Leaf Phenology in a Wet - Dry Tropical Savanna near Darwin, Northern Australia
Authors: Myers Bronwyn A. , Duff G. A. , Eamus D. , Fordyce I. R. , O'Grady A. , Williams R. J.
Published: August 2004

The seasonal variation in leaf xylem pressure potential at dawn
(ψdawn), leaf tissue water characteristics and daily
maximum leaf conductance was measured in eight woody species in a
wet–dry tropical savanna near Darwin, northern Australia, between
October 1992 and October 1993. The species were
Eucalyptus miniata, E. tetrodonta,
E. clavigera,
Xanthostemon paradoxus,
Erythrophleum chlorostachys,
Planchonia careya,
Terminalia ferdinandiana and
Cochlospermum fraseri. The species represented the major
leaf phenological types, evergreen, semi-deciduous and fully deciduous. The
climate of the region is characterised by annual drought during the winter
months, when virtually no rain falls and vapour pressure deficit (VPD) in the
afternoon reaches 3 kPa for 5 consecutive months each year. Despite this
drought, ψdawn remained high (–1.3 to
–1.5 MPa in evergreen species and –0.5 to –1.5 MPa in
deciduous species) relative to those trees that experience summer drought in
temperate and arid Australia. There was a tendency for evergreen and
semi-deciduous species to maintain positive turgor to lower xylem pressure
potentials (mean osmotic potential at incipient plasmolysis,
π0 = –2.15 MPa) than the fully
deciduous species (π0 = –2.03 MPa). For
all species, the daily maximum leaf conductance
(gmax) was maximal in the wet and
decreased during the dry season. Diurnally,
(gmax occurred near midday in the
wet season, but at about 0800–1000 hours during the dry season and the
‘buildup’, the transitional period between the dry and wet
seasons. There was substantial decrease in
(gmax (from 650–1000 mmol
m-2 s-1 in March to 200 mmol
m-2 s-1 in May) early in the dry
season in two of the three fully deciduous species
(Planchonia careya and
Cochlospermum fraseri). The dominant evergreen species
Eucalyptus miniata, by contrast, had high
gmax (> 400 mmol
m-2 s-1) throughout the dry
season, suggesting it had access to groundwater. For each species,
gmax declined with decreasing dawn
water potential in a log-linear manner; the slope of this relationship tended
to increase with increasing degree of deciduousness.
The Water Relations of Allosyncarpia ternata (Myrtaceae) at Contrasting Sites in the Monsoonal Tropics of Northern Australia
Authors: Fordyce I. R. , Duff G. A. , Eamus D.
Published: August 2004

Allosyncarpia ternata S.T.Blake (Myrtaceae) is an
evergreen tree, restricted largely to rocky habitats on the Arnhem Land
Plateau in the wet–dry tropics of northern Australia.
Allosyncarpia ternata grows in a wide range of habitats,
including sites near permanent springs, where it forms a distinctive
closed-canopy forest with an understorey of rainforest plants, and sites on
exposed cliffs and hilltops, where it occurs in open forest and woodland. Leaf
water relations differ markedly between these contrasting sites. During the
dry season, trees at open sites show strong diurnal hysteresis in stomatal
conductance (gs); afternoon
depressions in gs coincide with
regular afternoon increases in vapour pressure deficit. Pressure–volume
analyses indicate that A. ternata maintains turgor down
to leaf water potential values of about –2.8 MPa, close to the minimum
experienced by hilltop leaves late in the dry season. By contrast, trees on
the ravine floor, with year-round access to water, exhibit much smaller
diurnal and seasonal variation in stomatal conductance and little seasonal
variation in leaf water potential. It is concluded that this flexible response
in leaf water relations to seasonally dry conditions is partly responsible for
the ability of A. ternata to occupy and dominate the
vegetation in such a wide variety of habitats. The near confinement of the
species to the Arnhem Land Plateau is in part due to the water-holding
capacity of the bedrock.
Seasonal and Diurnal Patterns of Carbon Assimilation, Stomatal Conductance and Leaf Water Potential in Eucalyptus tetrodonta Saplings in a Wet - Dry Savanna in Northern Australia
Authors: Prior L. D. , Eamus D. , Duff G. A.
Published: August 2004

Seasonal and diurnal trends in carbon assimilation, stomatal conductance and
leaf water potential were studied using 1–3 m tall saplings of
Eucalyptus tetrodonta (F.Muell.). The study site was in
an unburnt savanna near Darwin, where rainfall is strongly seasonal. Mean
daily maximum assimilation rates ranged from 14.5 µmol
m-2 s-1 in May to 4.8 µmol
m-2 s-1 in October. There was a
linear relationship between daily maximum assimilation rates and pre-dawn leaf
water potential (r = 0.62,
n = 508) and a log–log linear relationship
between daily maximum stomatal conductance and pre-dawn leaf water potential
(r = 0.68, n = 508).
Assimilation rates and stomatal conductance were always higher in the morning
than in the afternoon, irrespective of season. Stomatal conductance responded
more strongly to leaf-to-air vapour pressure difference when pre-dawn leaf
water potentials were moderately low (–0.5 to –1.5 MPa) than when
they were very low (< –1.5 MPa) or high (> –0.5 MPa).
Assimilation decreased sharply when temperature exceeded 35˚C. Seasonal
trends in assimilation rate could be attributed primarily to stomatal closure,
but diurnal trends could not. High leaf temperatures were a major cause of
lower assimilation rates in the afternoon. Approximately 90% of leaves
were lost by the end of the dry season, and above-ground growth was very slow.
It is hypothesised that E. tetrodonta saplings allocate
most photosynthate to root and lignotuber growth in order to tolerate seasonal
drought and the high frequency of fire in northern Australian savannas.
Seasonal Patterns in Soil Moisture, Vapour Pressure Deficit, Tree Canopy Cover and Pre-dawn Water Potential in a Northern Australian Savanna
Authors: Duff G. A. , Myers B. A. , Williams R. J. , Eamus D. , O'Grady A. , Fordyce I. R.
Published: August 2004

The wet–dry tropics of northern Australia are characterised by extreme
seasonal variation in rainfall and atmospheric vapour pressure deficit,
although temperatures are relatively constant throughout the year.This
seasonal variation is associated with marked changes in tree canopy cover,
although the exact determinants of these changes are complex. This paper
reports variation in microclimate (temperature, vapour pressure deficit
(VPD)), rainfall, soil moisture, understorey light environment (total daily
irradiance), and pre-dawn leaf water potential of eight dominant tree species
in an area of savanna near Darwin, Northern Territory, Australia. Patterns of
canopy cover are strongly influenced by both soil moisture and VPD. Increases
in canopy cover coincide with decreases in VPD, and occur prior to increases
in soil moisture that occur with the onset of wet season rains. Decreases in
canopy cover coincide with decreases in soil moisture following the cessation
of wet season rains and associated increases in VPD. Patterns of pre-dawn
water potential vary significantly between species and between leaf
phenological guilds. Pre-dawn water potential increases with decreasing VPD
towards the end of the dry season prior to any increases in soil moisture.
Decline in pre-dawn water potential coincides with both decreasing soil
moisture and increasing VPD at the end of the dry season. This study
emphasises the importance of the annual transition between the dry season and
the wet season, a period of 1–2 months of relatively low VPD but little
or no effective rainfall, preceded by a 4–6 month dry season of no
rainfall and high VPD. This period is accompanied by markedly increased canopy
cover, and significant increases in pre-dawn water potential, which are
demonstrably independent of rainfall. This finding emphasises the importance
of VPD as a determinant of physiological and phenological processes in
Australian savannas.
Grass-mediated Capture of Resource Flows and the Maintenance of Banded Mulga in a Semi-arid Woodland
Authors: Anderson Val Jo , Hodgkinson Ken C.
Published: August 2004

It has been proposed for semi-arid and arid regions that the scarce resources
of water and nutrients normally limiting plant growth are distributed patchily
in the landscape in order to maintain both stability and productivity (Tongway
1990). ‘Fertile patches’ are maintained by the concentration of
resources during flows and when resource control is weakened their persistence
is threatened. This proposition was tested by comparing water relations of
perennial life-forms in the nutrient and water rich ‘island-bands’
of mulga (Acacia aneura F.Muell. ex Benth.) shrubs, with
and without perennial grasses. Dawn xylem water potential (dawn
ψx) and stable hydrogen isotope composition data
showed that A. aneura and companion grasses competed for
soil water, whereas the poplar box (Eucalyptus populnea
F.Muell.) trees accessed additional sub-soil water. During a drying cycle,
dawn ψx of A. aneura on the
upslope portion of ‘island-bands’ was –2 MPa where grass was
abundant, and –4.8 MPa where grasses were killed by heavy grazing. On
the downslope portions, dawn ψx of
A. aneura was similar at –4.2 MPa. Recruitment of
A. aneura was occurring in the upslope portion, but was less where there were
no grasses. There were more dead A. aneura shrubs on the
downslope portion and in grass-free ‘island-bands’. The results
suggest that removal of perennial grasses by grazing shortens the period of
water supply to A. aneura shrubs in ‘island-bands’ and they
prematurely die during low rainfall periods. Furthermore, continued grazing
pressure from domestic and non-domestic herbivores will prevent restoration of
landscape processes necessary for the survival of these shrubs and associated
flora.
Xylem Embolism in Seedlings and Resprouts of Adenostoma fasciculatum after Fire
Authors: Williams Jann E. , Davis Stephen D. , Portwood Kim
Published: August 2004

Mediterranean-type ecosystems experience prolonged summer drought. By the timeof the first summer after a wildfire the root systems of seedlings aregenerally not developed enough to tap deep moisture resources, so seedlingsoften surpass their limits of tolerance to water stress, and mortality ishigh. Selective pressures therefore are possibly greater during the firstsummer drought after wildfire than at any other stage. Seedlings ofAdenostoma fasciculatum Hook. & Arn. (chamise), oneof the most common types of chaparral shrubs in southern California, whichestablished after a wildfire in November 1993, had water potentials as low as–10 MPa at the end of summer 1994. Such low water potentials in woodyplants are known to cause air emboli formation in xylem vessels and tracheids,potentially blocking water transport. By contrast, water potentials of theresprouts of chamise did not fall below –4.5 MPa. A comparative study ofchamise seedlings and resprouts was initiated to ascertain whether the degreeof xylem embolism was correlated with observed differences in minimum waterpotential and differential mortality (seedlings 79%, resprouts <1%) of these two life stages. A newly developed technique was used thatallows measurement of individuals with low levels of hydraulic conductance.Embolism (calculated as percentage loss in hydraulic conductance due to airemboli) was measured on whole shoots of seedlings and similar-sized branchletsof resprouts collected at a field site in the Santa Monica Mountains.Seedlings with extremely low water potentials (–9.8 ± 1.7 MPa,s.e., n = 10) were highly embolised (embolism= 82.8 ± 2.0%). Resprouts, with an average waterpotential of –3.8 ± 1.8 MPa, exhibited quite moderate levels ofembolism (26.0 ± 4.6%). These values suggest that xylem embolismmay have contributed to the high seedling mortality rate. Seedlings known tohave very low water potentials showed a significant decrease in levels ofembolism (63.2 ± 6.1%, s.e., n = 4)after a rainfall event of 31 mm. Investigations suggested that this was due topositive stem pressures in seedlings during or soon after the rainfall eventcausing refilling. The timing of post-fire rainfall events may be a criticalfactor in the survival and establishment of chamise seedlings.
Grossplots: a Method for Estimating the Temperature State of the Earth and of Australia, Cretaceous to Middle Miocene
Authors: Frakes L. A.
Published: August 2004

Grossplots are compilations of globally distributed palaeotemperature data
onto latitude versus age plots, which are then contoured. The results
specifically show the distribution of temperature over the globe and its
variations over the Cretaceous to Middle Miocene interval. Data for continents
and oceans are plotted separately in this investigation, and each such
grossplot is in accord with the known climate changes of this time. The
general scarcity of quantitative palaeotemperature information for Australia
can be rectified by deriving, from the global continental grossplot, the
relationship between mean annual temperature and latitude. When these are
applied to the latitude band progressively occupied by Australia, the
following observations can be made: (1) during the Early Cretaceous, the
south-east of the continent was subjected to freezing wintertime temperatures;
(2) peak warming of northern Australia was attained in the
Turonian–Santonian, but this was followed by cooling later in the
Cretaceous; (3) Early Tertiary warming until the Late Eocene particularly
affected the northern half of the continent, but this region then underwent
the most severe cooling in the Early Oligocene; (4) subsequently, the whole of
the continent cooled uniformly from conditions only slightly warmer than at
present. Despite Australia’s equatorward march, the Late Cretaceous to
Palaeocene climates of the continent have been influenced more effectively by
changes in the global climate state. However, global cooling since the Eocene
has been less effective than drift in controlling the warming climate of
Australia. The time–space distribution of precipitation over Australia
is estimated from the global relationship between terrestrial temperature and
rainfall. The Eocene experienced the heaviest rainfall (> 1560 mm
year-1, in the north only), and the Eocene to Middle
Miocene experienced moderately high rates (> 500 mm
year-1 in the northern three-quarters of the continent).
Tertiary brown coals in southern regions were formed in proximity to areas of
high rainfall. Continentwide low rates (< 500 mm
year-1; semi-arid) are suggested for the Cretaceous,
except for wet conditions in the north during the Albian–Santonian and
the Late Maastrichtian. Estimates of precipitation are subject to factors such
as continentality and location of moisture sources, which cannot be evaluated
at present.
The Development of a Diatom Database for Inferring Lake Salinity, Western Victoria, Australia: Towards a Quantitative Approach for Reconstructing Past Climates
Authors: Gell Peter A.
Published: August 2004

The development of a modern data set of 156 diatom samples from salt lakes has
provided evidence of the tolerance of a large number of taxa to the salinity
of lake waters. Thirty taxa have been recorded from 30 or more samples and so
have been well characterised. A further 42 taxa have been recorded from 10 or
more samples. The lakes sampled range in salinity from the
freshwater–oligosaline boundary to well into the hypersaline range, so
the upper and lower salinity tolerance limits of many species were
investigated. Canonical correspondence analysis of the data set showed that
salinity was the most important of the tested parameters influencing the
diatom assemblages in the samples. Randomisation tests have provided
correlation values between measured and predicted salinity comparable with
those gained from other major salt lake diatom data sets, suggesting that this
set is a good predictor of lake salinity.
Effects of Host Age on Development of Cavity Spot Disease of Carrots Caused by Pythium coloratum in Western Australia Khaled
Authors: El-Tarabily A. , Hardy Giles E. St J. , Sivasithamparam Krishnapillai
Published: August 2004

Three experiments were conducted with Pythium coloratum
Vaartaja, a causal agent of cavity spot disease of carrots in Western
Australia, to study the relationships between host age, time of infection and
development of cavity spot lesions. Pythium coloratum
was isolated frequently from 3-6-week-old asymptomatic roots of carrots grown
in soils infested naturally or artificially with the pathogen. Carrots grown
in containers of soil artificially infested with
P. coloratum, but not those in naturally infested field
soil, developed cavity spot lesions after 6 weeks. Early infection of carrot
seedlings at or before 3 weeks by P. coloratum in
artificially infested soils followed by their transfer to pathogen-free soil
was sufficient to cause cavity spot disease at the time of harvest (16 weeks).
The disease levels in this treatment were not different from those transferred
to P. coloratum-infested soil. There was no significant
(P > 0.05) association between carrot age and the
ability of P. coloratum to infect the roots and to cause
cavity spot lesions at harvest.