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The barley grass stripe rust (BGYR) pathogen Puccinia striiformis f. sp. pseudohordei was first detected in Australia in 1997. While studies have established that it is virulent on wild barley grass, and can infect several barley cultivars, the basis of genetic resistance to this pathogen in barley is largely unknown. Understanding the genetic basis of host resistance and ensuring the selection of germplasm with multiple resistance genes are important to mitigate the potential impact of BGYR in barley production. Genetic analysis of seedling resistance to BGYR in two barley doubled haploid populations, Amaji Nijo/WI2585 (AN/WI) and Galleon/Haruna Nijo (GL/HN), indicated that resistance is governed by several genes. Marker regression analysis of the seedling resistance data from the AN/WI population detected a major QTL, BGYR_WI1 (resistance contributed by WI2585 with the closest marker explaining 52 % of the total phenotypic effect) on chromosome 1HS, flanked by the loci Xabg59 and Xabc310b at map positions 0.0 and 6.9 cM, respectively. Similarly, a major QTL, BGYR_HN1, (resistance contributed by Haruna Nijo with the closest marker explaining 70 % of the total phenotypic effect) was detected in the GL/HN population and was mapped to 1HS, flanked by the loci Xbcd135 and XHOR1 at map positions 12.8 and 24.5 cM, respectively. In addition, several minor loci that provided resistance against BGYR were detected in both populations. While defined QTL intervals were large, the analysis nonetheless provides new information on sources of major QTL controlling resistance to BGYR.

Under rising temperature, the rate of any developmental process increased with temperature more rapidly than that of CO2 assimilation. We found that this discrepancy, summarised by the CO2 assimilation rate per unit of plant development, could explain the observed reductions in biomass accumulation in leaves and grain under high temperatures. This simple model describes the effects of night and day temperature equally well, and offers a simple framework for describing the effects of temperature on plant growth, without any supplementary effect of rising night temperatures., There is a growing consensus in the literature that rising temperatures influence the rates of biomass accumulation by shortening the development of plant organs and the whole plant and by altering the rates of respiration and photosynthesis. A model describing the net effects of these processes on biomass would be useful, but would need to reconcile reported differences in the effects of night and day temperature on plant productivity. In this study, the working hypothesis was that the temperature responses of CO2 assimilation and plant development rates were divergent, and that their net effects could explain observed differences in biomass accumulation. In wheat (Triticum aestivum) plants, we followed the temperature responses of photosynthesis, respiration and leaf elongation, and confirmed that their responses diverged. We measured the amount of carbon assimilated per ‘unit of plant development’ in each scenario and compared it to the biomass that accumulated in growing leaves and grains. Our results suggested that, up to a temperature optimum, the rate of any developmental process increased with temperature more rapidly than that of CO2 assimilation and that this discrepancy, summarised by the CO2 assimilation rate per unit of plant development, could explain the observed reductions in biomass accumulation in plant organs under high temperatures. The model described the effects of night and day temperature equally well, and offers a simple framework for describing the effects of temperature on plant growth.

Velvet tobacco mottle virus (VTMoV) is a naturally occurring mirid-transmitted sobemovirus of native velvet tobacco (Nicotiana velutina) plants in the Australian arid zone. We have sequenced the coding region of a typical field isolate of VTMoV (isolate I-17-04, satellite-plus) and show that it differed by nine polymorphisms from the previously sequenced atypical ‘satellite-minus’ variant VTMoV-K1 (represented here as L-K1-04), while retaining the same genomic and amino acid sequence motifs. We also report that although L-K1-04 was confirmed to be free of detectable satellite RNA by gel electrophoretic assay, the satellite sequence was detected in it by RT-PCR assay. Nucleotide sequence variation among the RNA-dependent RNA polymerase open reading frames of 15 field and laboratory isolates identified four phylogenetic groups, but these did not show a pattern related to site or time of sampling. This result would be consistent with nucleotide sequence variants of VTMoV being dispersed widely by migrating adult mirid vectors.

Barley yellow dwarf disease (BYD) is transmitted by aphids and is caused by different strains of Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV). Economically it is one of the most important diseases of cereals worldwide. Besides chemical control of the vector, growing of tolerant/resistant cultivars is an effective way of protecting crops against BYD. The Ryd3 gene in barley (Hordeum vulgare L.) confers tolerance to BYDV-PAV and BYDV-MAV and the locus was previously mapped on the short arm of barley chromosome 6H near the centromere. We applied a strategy for high-resolution mapping and marker saturation at the Ryd3 locus by exploiting recent genomic tools available in barley. In a population of 3,210 F2 plants, 14 tightly linked markers were identified, including 10 that co-segregated with Ryd3. The centromeric region where Ryd3 is located suffers suppressed recombination or reduced recombination rate, suggesting potential problems in achieving (1) map-based cloning of Ryd3 and (2) marker selection of the resistance in breeding programmes without the introduction of undesirable traits via linkage drag.

Within the cereal grasses, variation in inflorescence architecture results in a conspicuous morphological diversity that in crop species influences the yield of cereal grains. Although significant progress has been made in identifying some of the genes underlying this variation in maize and rice, in the temperate cereals, a group that includes wheat, barley, and rye, only the dosage-dependent and highly pleiotropic Q locus in hexaploid wheat has been molecularly characterized. Here we show that the characteristic variation in the density of grains along the inflorescence, or spike, of modern cultivated barley (Hordeum vulgare) is largely the consequence of a perturbed interaction between microRNA172 and its corresponding binding site in the mRNA of an APELATA2 (AP2)-like transcription factor, HvAP2. We used genome-wide association and biparental mapping to identify HvAP2. By comparing inflorescence development and HvAP2 transcript abundance in an extreme dense-spike mutant and its nearly isogenic WT line, we show that HvAP2 turnover driven by microRNA 172 regulates the length of a critical developmental window that is required for elongation of the inflorescence internodes. Our data indicate that this heterochronic change, an altered timing of developmental events caused by specific temporal variation in the efficiency of HvAP2 turnover, leads to the striking differences in the size and shape of the barley spike.

The Ror1 gene was fine-mapped to the pericentric region of barley chromosome 1HL. Recessively inherited loss-of-function alleles of the barley (Hordeum vulgare) Mildew resistance locus o (Mlo) gene confer durable broad-spectrum disease resistance against the obligate biotrophic fungal powdery mildew pathogen Blumeria graminis f.sp. hordei. Previous genetic analyses revealed two barley genes, Ror1 and Ror2, that are Required for mlo-specified resistance and basal defence. While Ror2 was cloned and shown to encode a t-SNARE protein (syntaxin), the molecular nature or Ror1 remained elusive. Ror1 was previously mapped to the centromeric region of the long arm of barley chromosome 1H. Here, we narrowed the barley Ror1 interval to 0.18 cM and initiated a chromosome walk using barley yeast artificial chromosome (YAC) clones, next-generation DNA sequencing and fluorescence in situ hybridization. Two non-overlapping YAC contigs containing Ror1 flanking genes were identified. Despite a high degree of synteny observed between barley and the sequenced genomes of the grasses rice (Oryza sativa), Brachypodium distachyon and Sorghum bicolor across the wider chromosomal area, the genes in the YAC contigs showed extensive interspecific rearrangements in orientation and order. Consequently, the position of a Ror1 homolog in these species could not be precisely predicted, nor was a barley gene co-segregating with Ror1 identified. These factors have prevented the molecular identification of the Ror1 gene for the time being.

In cereals, a common salinity tolerance mecha- nism is to limit accumulation of Na ? in the shoot. In a cross between the barley variety Barque-73 (Hordeum vulgare ssp. vulgare) and the accession CPI-71284 of wild barley (H. vulgare ssp. spontaneum), the HvNax3 locus on chro- mosome 7H was found to determine a *10-25 % differ- ence in leaf Na ? accumulation in seedlings grown in saline hydroponics, with the beneficial exclusion trait originating from the wild parent. The Na ? exclusion allele was also associated with a 13-21 % increase in shoot fresh weight. The HvNax3 locus was delimited to a 0.4 cM genetic interval, where it cosegregated with the HVP10 gene for vacuolar H ? -pyrophosphatase (V-PPase). Sequencing revealed that the mapping parents encoded identical HVP10 proteins, but salinity-induced mRNA expression of HVP10 was higher in CPI-71284 than in Barque-73, in both roots and shoots. By contrast, the expression of several other genes predicted by comparative mapping to be located in the HvNax3 interval was similar in the two parent lines. Previ- ous work demonstrated roles for V-PPase in ion transport and salinity tolerance. We therefore considered transcrip- tion levels of HVP10 to be a possible basis for variation in shoot Na ? accumulation and biomass production controlled by the HvNax3 locus under saline conditions. Potential mechanisms linking HVP10 expression patterns to the observed phenotypes are discussed.

Abiotic stresses, including drought, heat, cold, acid soils, salinity, and low nutrient availability, severely reduce wheat yield and are a problem for farmers worldwide. These conditions are unpredictable in their timing and location in the field, hindering effective selection for tolerance. Wheat has a number of adaptations and genes to enable it to grow during periods of stress. Future breeding and transgenic approaches to improve wheat yield rely on the identification, characterization, and selection of these genes. This article will outline the various abiotic stress adaptations of wheat to abiotic stress and the genes encoding them.

Brief heat events (1–3 days, >30 °C) commonly reduce wheat (Triticum aestivum L.) grain size and consequently yield. To identify mechanisms of tolerance to such short heat events, 36 wheat genotypes were treated under day/night temperatures of 37 °C/27 °C for 3-days in a growth chamber, at 10 days after anthesis, and a range of developmental, chlorophyll and yield-related traits monitored. The degree of flag leaf chlorophyll loss during the treatment was the variable that showed the highest correlation to grain weight loss (r = 0.63; p

Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section.

Genomic mutation in plant viruses of cultivated plants is known to be influenced by virus, host and vector, but the factors influencing mutation in viruses of native plants in natural ecosystems are rarely studied. We have tested the effect of mode of transmission on mutation in Velvet tobacco mottle virus (VTMoV), a mirid-vectored sobemovirus associated with Nicotiana velutina, an Australian native xerophyte growing in a region isolated from anthropogenic influences. Two variants of VTMoV (K1 and R17) were passaged monthly in the alternative experimental plant host, N. clevelandii, for 2 years, either by mechanical inoculation or by transmission with the mirid Cyrtopeltis nicotianae. Sequence variations were scored after 24 passages in regions of the genome containing the open reading frames (ORFs) for the P1 and coat protein (CP). The mean mutation rate was 6.83 × 10(-4) nt/site year, but a higher overall rate was observed for the K1 (satellite -) than the R17 (satellite +) variant. The P1 ORF showed a higher frequency of non-synonymous mutations than the CP. No clear association was found between either mutation site or mutation rate and the mode of transmission, indicating that obligatory mirid transmission had not exerted a specific bottle-neck effect on sequence variation during the experimental time frame. Failure to detect any sequence motifs linked to vector transmission suggests that a specific capsid-stylet interaction is not required for transmission by mirids.

Little is known about the ecology of warmwater fish in small coastal embayments ( Lepomis gibbous ) as a model warmwater fish, we compare hatch dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario, in a warmer and cooler year. In 2007, the embayments differed by approximately 2–5 °C until late-July. In that year, temperatures in the cooler embayment delayed hatching times until July 18–August 20, approximately eight weeks later (May 24–August 20) than in the warmer embayment. Almost all offspring in the cooler embayment were likely too small to survive the winter. In 2008 both embayments had similar temperatures. In that year, pumpkinseed started hatching in early-June, and most were likely large enough to survive the winter. The findings from the two intensively sampled embayments were confirmed with a 21-year fish monitoring dataset; adult pumpkinseed were captured in the littoral zone of warm embayments 6–8 weeks earlier than in cooler embayments. Relative to pumpkinseed in the small inland lakes of eastern and central Ontario, spawning is delayed by at least two weeks in coastal embayments. Using water temperatures as a surrogate for growth, we calculated that only 5 of the 17 embayments for which we have temperature records were able to consistently produce successfully overwintering age-0 fish. Nevertheless, we found pumpkinseed age ≥ 1 in embayments too cold to produce age-0 pumpkinseed, suggesting immigration from warmer embayments.

Coastal embayments have been and will continue to be constructed along the northwest shoreline of Lake Ontario to restore and create warmwater fish habitat. However, very little is known about the biological connections among embayments. Using otolith microchemistry on pumpkinseed, largemouth bass and yellow perch collected from three constructed embayments in 2006–2009, we confirm that these three species of fish each exist in a metapopulation. We find that juvenile pumpkinseed, largemouth bass and yellow perch occupy embayments different from their natal habitat after their first winter, and for at least pumpkinseed, continue to move among embayments after their second winter. We hypothesize that these fishes move among embayments after haphazardly dispersing from their overwintering habitat to the littoral zone each spring. Habitat restoration and remediation efforts in coastal Great Lakes habitats should take a system-based management approach that considers the spatial proximity of embayments, and attempts to create or preserve connected networks.

Most experiments on effects of anti-predator behaviours use small enclosures and study behaviour and development of prey in the constant and immediate presence of predators. While useful, such studies are difficult to relate to natural situations where prey and predators are unrestricted. We describe a system designed specifically to estimate the impact of fish on foraging of larval Chironomus tentans under field levels of encounters with fish. The system involves raceways designed to control movement of fish over patches of chironomids so the impact of realistic, short-term encounters between predators and prey could be measured. Fish passes significantly reduced foraging activity, but the reduction was small (median of 1.16 min·fish event-1·larvae-1, or 6.5% of the time normally spent active) and did not depend on larval hunger nor fish size or species. Other laboratory experiments using large wading pools indicated 15 cm was the best estimate of the distance over which larvae respond to fish....

Genes that enable crops to limit Na(+) accumulation in shoot tissues represent potential sources of salinity tolerance for breeding. In barley, the HvNax4 locus lowered shoot Na(+) content by between 12% and 59% (g(-1) DW), or not at all, depending on the growth conditions in hydroponics and a range of soil types, indicating a strong influence of environment on expression. HvNax4 was fine-mapped on the long arm of barley chromosome 1H. Corresponding intervals of ∼200 kb, containing a total of 34 predicted genes, were defined in the sequenced rice and Brachypodium genomes. HvCBL4, a close barley homologue of the SOS3 salinity tolerance gene of Arabidopsis, co-segregated with HvNax4. No difference in HvCBL4 mRNA expression was detected between the mapping parents. However, genomic and cDNA sequences of the HvCBL4 alleles were obtained, revealing a single Ala111Thr amino acid substitution difference in the encoded proteins. The known crystal structure of SOS3 was used as a template to obtain molecular models of the barley proteins, resulting in structures very similar to that of SOS3. The position in SOS3 corresponding to the barley substitution does not participate directly in Ca(2+) binding, post-translational modifications or interaction with the SOS2 signalling partner. However, Thr111 but not Ala111 forms a predicted hydrogen bond with a neighbouring α-helix, which has potential implications for the overall structure and function of the barley protein. HvCBL4 therefore represents a candidate for HvNax4 that warrants further investigation.

To evaluate the importance of non-consumptive effects of predators on prey life histories under natural conditions, an index of predator abundance was developed for naturally occurring populations of a common prey fish, the yellow perch Perca flavescens, and compared to life-history variables and rates of prey energy acquisition and allocation as estimated from mass balance models. The predation index was positively related to maximum size and size at maturity in both male and female P. flavescens, but not with life span or reproductive investment. The predation index was positively related to size-adjusted specific growth rates and growth efficiencies but negatively related to model estimates of size-adjusted specific consumption and activity rates in both vulnerable (small) and invulnerable (large) size classes of P. flavescens. These observations suggest a trade-off between growth and activity rates, mediated by reduced activity in response to increasing predator densities. Lower growth rates and growth efficiencies in populations with fewer predators, despite increased consumption suggests either 1) a reduction in prey resources at lower predator densities or 2) an intrinsic cost of rapid prey growth that makes it unfavourable unless offset by a perceived threat of predation. This study provides evidence of trade-offs between growth and activity rates induced by predation risk in natural prey fish populations and illustrates how behavioural modification induced through predation can shape the life histories of prey fish species.

With 3 figures and 2 tables Abstract Tolerance to soil boron toxicity, salinity and zinc deficiency is required for maintaining adequate yields on many soils, while a high content of zinc in the grain is desirable for human nutrition. To facilitate the identification of genes for these traits in barley, we constructed a bacterial artificial chromosome (BAC) library of the barley-doubled haploid line CS134 derived from a cross between the Australian malting variety ‘Clipper’ and the Algerian landrace Sahara 3771. CS134 contains tolerance alleles from Sahara 3771 at four boron tolerance loci, genes at two loci conferring high zinc content in seeds, and a gene from ‘Clipper’ that limits shoot sodium accumulation. The library contains 221184 clones and has an average insert size of around 120 kb, giving a 4.9-fold coverage of the barley genome. Clones were recovered from the library using probes closely linked to the boron tolerance locus on chromosome 4H. One of the positive BAC clones facilitated isolation and sequencing of the boron tolerance gene (Bot1) at this locus. Therefore, the BAC library represents a useful tool that could be used to isolate several genes of agronomic interest. In the process of constructing this library, we identified several technical modifications that improve the efficiency of BAC library construction.

Previous work identified the wild barley (Hordeum vulgare ssp. spontaneum) accession CPI-71284-48 as being capable of limiting sodium (Na(+)) accumulation in the shoots under saline hydroponic growth conditions. Quantitative trait locus (QTL) analysis using a cross between CPI-71284-48 and a selection of the cultivated barley (H. vulgare ssp. vulgare) cultivar Barque (Barque-73, a moderate Na(+) excluder) attributed the control of the Na(+) exclusion trait from CPI-71284-48 to a single locus on the short arm of chromosome 7H, which was named HvNax3. The locus reduced shoot Na(+) accumulation by 10-25% in plants grown in 150 mM NaCl. Markers generated using colinearity with rice and Brachypodium, together with the analysis of introgression lines and F(2) and F(3) families, enabled HvNax3 to be mapped to a 1.3-cM interval. Genes from the corresponding rice and Brachypodium intervals encode 16 different classes of proteins and include several plausible candidates for HvNax3. The potential of HvNax3 to provide a useful trait contributing to salinity tolerance in cultivated barley is discussed.

Exposure of flowering cereal crops to frost can cause sterility and grain damage, resulting in significant losses. However, efforts to breed for improved low temperature tolerance in reproductive tissues (LTR tolerance) has been hampered by the variable nature of natural frost events and the confounding effects of heading time on frost-induced damage in these tissues. Here, we establish conditions for detection of LTR tolerance in barley under reproducible simulated frost conditions in a custom-built frost chamber. An ice nucleator spray was used to minimize potential effects arising from variation in naturally occurring extrinsic nucleation factors. Barley genotypes differing in their field tolerance could be distinguished. Additionally, an LTR tolerance quantitative trait locus (QTL) on the long arm of barley chromosome 2H could be detected in segregating families. In a recombinant family, the QTL was shown to be separable from the effects of the nearby flowering time locus Flt-2L. At a minimum temperature of -3.5 degrees C for 2 h, detection of the LTR tolerance locus was dependent on the presence of the nucleator spray, suggesting that the tolerance relates to freezing rather than chilling, and that it is not the result of plant-encoded variation in ice-nucleating properties of the tiller surface.

Flowering time represents an important adaptive trait for temperate cereal crops and may also impact on frost damage in cereal reproductive tissues by enabling escape or by influencing accumulation of genuine tolerance. The Flowering time-2L (Flt-2L) quantitative trait locus (QTL) on the distal end of barley chromosome arm 2HL overlaps with QTL for rachis internode length and reproductive frost damage. Flt-2L was also found to be associated with plant height. By combining marker analysis with phenotyping in progeny families of selected Amagi Nijo x WI2585 F(6) recombinants, we were able to map quantitative flowering time, rachis internode length, and plant height effects on 2HL as discrete Mendelian traits. The three developmental characters showed codominant modes of expression and perfectly cosegregated with one another in a 1.3-cM marker interval, indicating control by the same gene or closely linked genes. Twelve genes were identified in the related intervals in the rice and Brachypodium distachyon genomes. The HvAP2 gene cosegregated with Flt-2L and represents a plausible candidate for Flt-2L, since it is highly similar to the wheat domestication gene Q which has similar developmental effects. These data will contribute to isolation of the Flt-2L gene(s) and help establish the basis of the frost damage QTL.

One of the major challenges facing fishery scientists and managers today is determining how fish populations are influenced by habitat conditions. Many approaches have been explored to address this challenge, all of which involve modeling at one level or another. In this paper, we explore a process-oriented model approach whereby the critical population processes of birth and death rates are explicitly linked to habitat conditions. Application of this approach to five species of Great Lakes fishes including: walleye (Sander vitreus), lake trout (Salvelinus namaycush), smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), and rainbow trout (Onchorynchus mykiss), yielded a number of insights into the modeling process. One of the foremost insights is that processes determining movement and transport of fish are critical components of such models since these processes largely determine the habitats fish occupy. Because of the importance of fish location, an individual-based model appears to be a nearly inescapable modeling requirement. There is, however, a paucity of field-based data directly relating birth, death, and movement rates to habitat conditions experienced by individual fish. There is also a paucity of habitat information at a fine temporal and spatial scale for many important habitat variables. Finally, the general occurrence of strong ontogenetic changes in the response of different life stages to habitat conditions emphasizes the need for a modeling approach that considers all life stages in an integrated fashion.

SUMMARY Barley ( Hordeum vulgare L.) leaf stripe is caused by the seed-borne fungus Pyrenophora graminea . We investigated microscopically and molecularly the reaction of barley embryos to leaf stripe inoculation. In the resistant genotype NIL3876- Rdg2a , fungal growth ceased at the scutellar node of the embryo, while in the susceptible near-isogenic line (NIL) Mirco- rdg2a fungal growth continued past the scutellar node and into the embryo. Pathogenchallenged embryos of resistant and susceptible NILs showed different levels of UV autofluorescence and toluidine blue staining, indicating differential accumulation of phenolic compounds. Suppression subtractive hybridization and cDNA amplified fragment-length polymorphism (AFLP) analyses of embryos identified P. graminea -induced and P. graminea -repressed barley genes. In addition, cDNA-AFLP analysis identified six pathogenicityassociated fungal genes expressed during barley infection but at low to undetectable levels during growth on artificial media. Microarrays representing the entire set of differentially expressed cDNA-AFLP fragments and 100 barley homologues of previously described defence-related genes were used to study gene expression changes at 7 and 14 days after inoculation in the resistant and susceptible NILs. A total of 171 significantly modulated barley genes were identified and assigned to four groups based on timing and genotype dependence of expression. Analysis of the changes in gene expression during the barley resistance response to leaf stripe suggests that the Rdg2a -mediated response includes cell-wall reinforcement, signal transduction, generation of reactive oxygen species, cell protection, jasmonate signalling and expression of plant effector genes. The identification of genes showing leaf stripe inoculation or resistance-dependent expression sets the stage for further dissection of the resistance response of barley embryo cells to leaf stripe.

The improvement of crop yield has been possible through the indirect manipulation of quantitative trait loci (QTLs) that control heritable variability of the traits and physiological mechanisms that determine biomass production and its partitioning. This article surveys how QTL-based approaches contribute to a better understanding of the genetic basis of crop performance under environmentally constrained conditions and critically analyzes how this knowledge can assist breeders accelerate the release of cultivars better able to cope with abiotic constraints. Crop performance is the end result of the action of thousands of genes and their interactions with environmental conditions and cultural practices. During the past century, conventional breeding has been very successful in constantly raising the yield potential of crops (Campos et al., 2004Go; Borlaug and Dowswell, 2005Go; Duvick, 2005Go). This was mainly achieved with little or no knowledge of the factors governing the genetic variability exploited by breeders for crop improvement (Blum, 1988Go; Borlaug, 2007Go). However, this approach may now be insufficient, because the pressure to provide improvements at a rapid pace will mount if global climate change increases the frequency and severity of abiotic constraints. Heat stress, drought, water-logging, and salinity will probably become more prevalent in certain areas, while there will be an increased demand for agricultural products and reduced availability of agricultural land and natural resources such as water and fertilizers. Consequently, the genetic dissection of the quantitative traits controlling the adaptive response of crops to abiotic stress is a prerequisite to allow cost-effective applications of genomics-based approaches to breeding programs aimed at improving the sustainability and stability of yield under adverse conditions.

Aluminum toxicity is a major problem in agriculture worldwide. Among the cultivated Triticeae, rye (Secale cereale L.) is one of the most Al tolerant and represents an important potential source of Al tolerance for improvement of wheat. The Alt4 Al-tolerance locus of rye contains a cluster of genes homologous to the single-copy Al-activated malate transporter (TaALMT1) Al-tolerance gene of wheat. Tolerant (M39A-1-6) and intolerant (M77A-1) rye haplotypes contain five and two genes, respectively, of which two (ScALMT1-M39.1 and ScALMT1-M39.2) and one (ScALMT1-M77.1) are highly expressed in the root tip, typically the main site of plant Al tolerance/susceptibility. All three transcripts are upregulated by exposure to Al. High-resolution genetic mapping identified two resistant lines resulting from recombination within the gene cluster. These recombinants exclude all genes flanking the gene cluster as candidates for controlling Alt4 tolerance, including a homolog of the barley HvMATE Al-tolerance gene. In the recombinants, one hybrid gene containing a chimeric open reading frame and the ScALMT1-M39.1 gene each appeared to be sufficient to provide full tolerance. mRNA splice variation was observed for two of the rye ALMT1 genes and in one case, was correlated with a ∼400-bp insertion in an intron.

Both limiting and toxic soil concentrations of the essential micronutrient boron represent major limitations to crop production worldwide. We identified Bot1 , a BOR1 ortholog, as the gene responsible for the superior boron-toxicity tolerance of the Algerian barley landrace Sahara 3771 (Sahara). Bot1 was located at the tolerance locus by high-resolution mapping. Compared to intolerant genotypes, Sahara contains about four times as many Bot1 gene copies, produces substantially more Bot1 transcript, and encodes a Bot1 protein with a higher capacity to provide tolerance in yeast. Bot1 transcript levels identified in barley tissues are consistent with a role in limiting the net entry of boron into the root and in the disposal of boron from leaves via hydathode guttation.

Short heat waves during grain filling can reduce grain size and consequently yield in wheat (Triticum aestivum L.). Grain weight responses to heat represent the net outcome of reduced photosynthesis, increased mobilisation of stem reserves (water-soluble carbohydrates, WSC) and accelerated senescence in the grain. To compare their relative roles in grain weight responses under heat, these characteristics were monitored in nine wheat genotypes subjected to a brief heat stress at early grain filling (37°C maximum for 3 days at 10 days after anthesis). Compared with the five tolerant varieties, the four susceptible varieties showed greater heat-triggered reductions in final grain weight, grain filling duration, flag leaf chla and chlb content, stem WSC and PSII functionality (Fv/Fm). Despite the potential for reductions in sugar supply to the developing grains, there was little effect of heat on grain filling rate, suggesting that grain size effects of heat may have instead been driven by premature senescence in the grain. Extreme senescence responses potentially masked stem WSC contributions to grain weight stability. Based on these findings, limiting heat-triggered senescence in the grain may provide an appropriate focus for improving heat tolerance in wheat.

We have developed an age-structured, spatially explicit model to estimate smallmouth bass (Micropterus dolomieu) population dynamics from the readily available habitat data of a lake. Habitat suitability models were used to rank the suitability of different sites throughout a lake for smallmouth bass. Population dynamics were then linked to the habitat suitabilities via a home range mechanism, a density-dependent mechanism and the ideal-free distribution theory. The home ranges are calculated as a function of size, the density-dependent mechanism assumes that habitat suitability will decrease as the density of fish at a site increases and the ideal-free distribution theory assumes fish will seek out more suitable habitats. When all fish are distributed throughout the lake, growth is calculated as a function of temperature and density. This consequently affects the fecundity of the mature females, survival of the young-of-year (YOY) and the number of fish recruited to the population in subsequent years. Sensitivity analyses indicated that the habitat alterations that increased YOY survival (increased temperature and total nesting habitat) had the greatest impact on population dynamics and suggests that conservation or restoration efforts should focus on the nesting (YOY) habitat. When validated, the model described the population indicators, total number of nests and fish, better than the spatial distribution of fish within the study lakes. These findings suggest that in its current state, the model may be successfully used to guide smallmouth bass population and habitat management practices. Future developments of the model are also discussed.

Multivariate analyses on benthic invertebrate methylmercury concentrations ((MeHg)) and water chemistry from 12 Quebec water bodies were used to guide the construction of simple, predictive models of benthic invertebrate (MeHg) in 23 lakes in Ontario and Quebec. Separate predictive models for collector-shredder and predatory benthic invertebrates were constructed using multiple regression and were assessed for their predictive utility by cross- validation. Predatory benthic invertebrate (MeHg) was negatively related to pH and positively related to dissolved organic carbon (DOC) concentration (cross-validation r 2 = 0.31). Collector-shredder (MeHg) was positively related to (DOC) only (cross-validation r 2 = 0.13). Predictive utility of our models is similar to or surpasses that observed in previously published zooplankton MeHg models tested against independently collected data. Significant environmental variables and their contribution to the overall explanatory power of benthic invertebrate MeHg models are similar to those found in zooplankton models, suggesting that in both pelagic and benthic food webs, pH and DOC are important indicators of MeHg bioavailability. Although seasonal patterns in invertebrate (MeHg) were examined, none was detected. These models represent an effective means of identifying water bodies of interest for researchers and for reconstructing past benthic invertebrate (MeHg) patterns using archived water chemistry data. Resume : Des analyses multidimensionnelles des concentrations de methylmercure ((MeHg)) chez les invertebres ben- thiques et de la chimie de l'eau de 12 milieux aquatiques du Quebec nous ont guides dans l'elaboration de modeles simples et predictifs des concentrations de (MeHg) chez les invertebres benthiques de 23 lacs de l'Ontario et du Que- bec. Nous avons construit des modeles distincts pour les invertebres benthiques collecteurs-dechiqueteurs et les preda- teurs a l'aide de regressions multiples et nous avons evalue par validation croisee leur utilite pour la prediction. Il y a une relation negative entre (MeHg) chez les invertebres benthiques predateurs et le pH et une relation positive avec le carbone organique dissous (DOC; r 2 de validation croisee = 0,31). (MeHg) des collecteurs-dechiqueteurs est seulement en correlation positive avec (DOC) (r 2 de validation croisee = 0,13). Les potentiels de prediction de nos modeles sont semblables ou superieurs a ceux des modeles de MeHg du zooplancton tires de la litterature et evalues avec des don- nees recoltees de facon independante. Les variables significatives du milieu et leur contribution au pouvoir explicatif global des modeles de MeHg des invertebres benthiques sont semblables a ceux trouves dans les modeles de zooplanc- ton, ce qui laisse croire que le pH et DOC sont d'importants indicateurs de la biodisponibilite de MeHg, tant dans les reseaux alimentaires pelagiques que benthiques. Bien que nous les ayons recherchees, nous n'avons pas trouve de ten- dances saisonnieres du (MeHg) chez les invertebres. Ces modeles sont des moyens efficaces pour identifier les milieux aquatiques interessants pour les chercheurs et pour reconstituer les patterns de (MeHg) du passe chez les invertebres benthiques a partir de donnees de qualite de l'eau accumulees en archives.

Sex-specific life history variation was examined among 72 populations of yellow perch Perca flavescens from Ontario, Canada. We sought to determine whether relationships could be applied to other populations to predict parameter values when life history data are not available. Each of the measured traits (early growth rate, maturation size and age, reproductive investment, and maximum size) varied two- to threefold among populations. Relationships were developed to predict standard calculations of life history traits from population-specific data for use in poorly sampled lakes. Associations between life history traits and environmental variables can be used in unsampled lakes. Early growth rate was positively related to lake surface area, while relative density was positively related to total dissolved solids. For both sexes, maximum body size was positively related to lake surface area and negatively related to growing degree-days. Additional variation in female maximum size was explained by a ...

Using lake trout ( Salvelinus namaycush ) and walleye ( Sander vitreus ) we examined the extent of error that is created when non-population-specific or non-sex-specific data are used to develop fishery sustainability models. To put biases in perspective we first compared relative differences in sustainable harvest rate estimates of fast and slow growing populations to the mean difference between species. Few estimates of early mortality exist for either species, and a sensitivity analysis indicated that sustainable harvest rate estimates varied by more than 90% with those available. To evaluate biases created by predicting life history traits we estimated maturation age from asymptotic length in populations whose life history parameters had been measured directly. Incorporating species-specific information produced maturation ages that were closer to those measured (mean difference 22%) than did the estimates from inter-specific relationships (mean difference 42%). This resulted in sustainability estimates from species-specific predictions being closer to those estimated using actual maturation data. In evaluating problems associated with using non-sex-specific data we found that estimates of maximum sustainable harvest rates increased when female-specific life history data were used (could only be done for walleye) instead of combined-sex data (mean change in the two populations was 7%). Analyses indicate that it is desirable to collect life history data on specific populations of lake trout and walleye. If this is not possible, estimates of maximum sustainable harvest rates are most influenced by variation in estimates of early mortality, followed by the taxonomic resolution used to estimate co-variation among life history traits, and finally the use of combined-sex versus female-specific data.

Life history variation among 60 Ontario populations of lake trout (Salvelinus namaycush), walleye (Sander vitreus), cisco (Coregonus artedii), and yellow perch (Perca flavescens) is presented and interpreted using a biphasic model of individual growth that specifically accounts for the significant shift in energy allocation that accompanies sexual maturity. We show that the constraints imposed on life history variation by the character of the biphasic growth model are such that optimal life histories will exhibit associations among growth parameters, reproductive investment, and mortality that are largely consistent with associations evident in both our data set and earlier empirical studies; the von Bertalanffy growth parameter k varies with reproductive investment, and both k and investment vary with adult mortality. Our analysis suggests that within a food web, life history parameters will shift in a predictable fashion with the decreases in mortality expected as one moves from primary consumers up toward top predators. This expectation is supported by the differences in life history parameters that we observe between the two top predators in our data set (lake trout and walleye) and the two mid-trophic level consumers (cisco and yellow perch). Resume : Nous presentons les variations dans les cycles biologiques de 60 populations ontariennes de touladis (Salve- linus namaycush), de dores (Sander vitreus), de ciscos de lac (Coregonus artedii) et de perchaudes (Perca flavescens) et les interpretons a l'aide d'un modele biphasique de croissance individuelle qui tient compte specifiquement du changement significatif d'allocation de l'energie qui accompagne la maturite sexuelle. Nous demontrons que les contraintes imposees a la variation du cycle biologique par les caracteristiques du modele de croissance biphasique sont telles que les cycles biologiques optimaux montrent des associations entre les parametres de croissance, l'investissement reproductif et la mortalite qui sont en grande partie compatibles avec les associations presentes dans nos donnees et celles d'etudes empiriques anterieures: le parametre de croissance de von Bertalanffy k varie en fonc- tion de l'investissement reproductif et tant k que l'investissement varient en fonction de la mortalite des adultes. Notre analyse indique qu'a l'interieur d'un reseau alimentaire, les parametres demographiques vont se deplacer dans un sens previsible en fonction du declin de la mortalite attendu lorsqu'on passe des consommateurs primaires aux predateurs superieurs. Cette prediction se realise dans les differences observees dans les parametres demographiques entre, d'une part, les deux predateurs superieurs (touladis, dores) et, d'autre part, les deux consommateurs de niveau intermediaire (ciscos, perchaudes). (Traduit par la Redaction) Shuter et al. 746

Activity costs can account for a major proportion of fish energy budgets and may trade off against observed growth rates in wild fish populations. Recent approaches to estimating activity costs in situ have used a contaminant–bioenergetic mass balance modelling approach, allowing for a broader examination of activity costs among populations compared with time-consuming alternative approaches. We report the results of this contaminant–bioenergetic modelling approach to estimating in situ activity costs compared with two alternative independent methods of assessing in situ activity costs. Comparisons were made between a fast- and slow-growing yellow perch (Perca flavescens) population. Contaminant–bioenergetic estimates of activity costs in the fast-growing population were 39% lower than those in the slow-growing population. Activity estimated from recorded swimming behaviours was 37% lower in the fast-growing population and 22%–29% lower in the fast-growing population based on published relationships between activity costs and axial white muscle glycolytic enzyme capacities. Consumption rates were actually 32% lower in the fast-growing population, implying that lower activity costs more than compensated for lower food intake. The agreement among the three independent measures of activity costs strongly support the idea that activity costs, rather than food intake, are a major determinant of growth differences in these two wild fish populations.

Covariations of growth, age and size at maturity, and adult natural mortality rates are described for 22 Great Lakes stocks and 28 inland lake populations of lake whitefish ( Coregonus clupeaformis ). An understanding of these covariations could be used to modify the expectations of sustainable yields. Age at maturity was inversely related to pre-reproductive growth rates (ω = L ∝ k). Size at age 1 was significantly correlated with pre-reproductive growth rates, indicating that ωis a reali stic index of early growth. Age, but not length at maturity was inversely correlated with pre-reproductive growth rates. Asymptotic sizes (L ∝ ) were not correlated with age at maturity, however the time required to achieve asymptotic size was positively correlated with age at maturity. Pre-reproductive growth rates and asymptotic sizes were larger for Great Lakes whitefish than for inland lake whitefish. Great Lakes stocks matured at a younger age apparently due to higher pre-reproductive growth rates. Natural mortality rates were inversely related to age at maturity. These intraspecific covariations of growth and maturity are consistent with life history theory developed from interspecific analyses. Life history theory derived from interspecific analyses can, therefore, be applied to intraspecific variations in life history traits.

Sexual size dimorphism of walleye (Stizostedion vitreum vitreum) is achieved by females having higher growth rates than males before and after maturation, resulting in females with greater asymptotic sizes. Mercury (Hg) concentrations in epaxial muscle by age and weight for 31 populations of walleye were used to evaluate the relative importance of differences in consumption and activity in generating sexual size dimorphism. Growth efficiency by sex, age, and maturity is estimated by a ratio of annual increments in weight (g) to annual increments of Hg (mg), using the pooled changes in weight and Hg loadings of males and females from all lakes. The higher growth rates of females arise from greater consumption and higher growth efficiency. Growth efficiency of both sexes is similar before maturity, but the growth efficiency of mature males is substantially lower than that of either immature males or mature females. We propose that the inferior growth efficiency of males is a function of the greater activity of males, particularly during the spawning season when scramble competition for fertilization is likely to produce substantial increases in male fitness as a result of increased efforts to find and spawn with females.

The majority of verified plant disease resistance genes isolated to date are of the NBS-LRR class, encoding proteins with a predicted nucleotide binding site (NBS) and a leucine-rich repeat (LRR) region. We took advantage of the sequence conservation in the NBS motif to clone, by PCR, gene fragments from barley representing putative disease resistance genes of this class. Over 30 different resistance gene analogs (RGAs) were isolated from the barley cultivar Regatta. These were grouped into 13 classes based on DNA sequence similarity. Actively transcribed genes were identified from all classes but one, and cDNA clones were isolated to derive the complete NBS-LRR protein sequences. Some of the NBS-LRR genes exhibited variation with respect to whether and where particular introns were spliced, as well as frequent premature polyadenylation. DNA sequences related to the majority of the barley RGAs were identified in the recently expanded public rice genomic sequence database, indicating that the rice sequence can be used to extract a large proportion of the RGAs from barley and other cereals. Using a combination of RFLP and PCR marker techniques, representatives of all barley RGA gene classes were mapped in the barley genome, to all chromosomes except 4H. A number of the RGA loci map in the vicinity of known disease resistance loci, and the association between RGA S-120 and the nematode resistance locus Ha2 on chromosome 2H was further tested by co-segregation analysis. Most of the RGA sequences reported here have not been described previously, and represent a useful resource as candidates or molecular markers for disease resistance genes in barley and other cereals.

Lack of the barley (Hordeum vulgare) seven-transmembrane domain MLO protein confers resistance against the fungal pathogen Blumeria graminis f. sp.hordei (Bgh). To broaden the basis for MLO structure/function studies, we sequenced additionalmlo resistance alleles, two of which confer only partial resistance. Wild-type MLO dampens the cell wall-restricted hydrogen peroxide burst at points of attempted fungal penetration of the epidermal cell wall, and in subtending mesophyll cells, it suppresses a second oxidative burst and cell death. Although theBgh-induced cell death in mlo plants is spatially and temporally separated from resistance, we show that the two processes are linked. Uninoculated mutant mlo plants exhibit spontaneous mesophyll cell death that appears to be part of accelerated leaf senescence. Mlo transcript abundance increases in response to Bgh, rice (Oryza sativa) blast, wounding, paraquat treatment, a wheat powdery mildew-derived carbohydrate elicitor, and during leaf senescence. This suggests a broad involvement of Mlo in cell death protection and in responses to biotic and abiotic stresses.

Plants are under continuous threat of infection by pathogens endowed with diverse strategies to colonize their host. Comprehensive biochemical and genetic approaches are now starting to reveal the complex signaling pathways that mediate plant disease resistance. Initiation of defense signaling often involves specific recognition of invading pathogens by the products of specialized host resistance (R) genes. Potential resistance signaling components have been identified by mutational analyses to be required for specific resistance in the model Arabidopsis and some crop species. Strikingly, many of the components share similarity to that of innate immune systems in animals. Evidence is also accumulating that plant pathogens have a number of ways to evade host defenses during the early stages of infection, similar to animal pathogens. These strategies are becoming much better understood in a number of plant-pathogen interactions. In this review, we focus on the current knowledge of host factors that control plant resistance and susceptibility to fungal pathogens. The knowledge accumulated in these studies will serve a fundamental basis for combating diseases in strategic molecular agriculture.

Regions of amino acid conservation in the NBS domain of NBS-LRR resistance proteins facilitated the PCR isolation of eight resistance gene analog (RGA) sequences from genomic DNA of rice, barley, and Aegilops tauschii. These clones and other RGAs previously isolated from maize, rice, and wheat were assigned to 13 classes by DNA-sequence comparison and by their patterns of hybridisation to restricted barley DNA. Using a doubled-haploid mapping population, probes from 12 RGA classes were used to map 17 loci in the barley genome. Many of these probes have been used for mapping in wheat, and the collective data indicate that the positions of orthologous RGAs are conserved between barley and wheat. RGA loci were identified in the vicinity of barley leaf rust resistance loci Rph4, Rph7, and Rph10. Recombinants were identified between RGA loci and Rph7 and Rph10, while a cluster of RGA sequences detected by probe 5.2 cosegregated with Rph4 in 55 F2lines.Key words: barley, Hordeum vulgare, rust, Puccinia, resistance gene analog, RGA, resistance.

Rp1 is a complex rust resistance locus of maize. The HRp1-D haplotype is composed of Rp1-D and eight paralogues, seven of which also code for predicted nucleotide binding site-leucine rich repeat (NBS-LRR) proteins similar to the Rp1-D gene. The paralogues are polymorphic (DNA identities 91-97%), especially in the C-terminal LRR domain. The remaining family member encodes a truncated protein that has no LRR domain. Seven of the nine family members, including the truncated gene, are transcribed. Sequence comparisons between paralogues provide evidence for past recombination events between paralogues and diversifying selection, particularly in the C-terminal half of the LRR domain. Variants selected for complete or partial loss of Rp1-D resistance can be explained by unequal crossing over that occurred mostly within coding regions. The Rp1-D gene is altered or lost in all variants, the recombination breakpoints occur throughout the genes, and most recombinant events (9/14 examined) involved the same untranscribed paralogue with the Rp1-D gene. One recombinant with a complete LRR from Rp1-D, but the aminoterminal portion from another homologue, conferred the Rp1-D specificity but with a reduced level of resistance.

We describe the development of polymerase chain reaction-based, sequence-tagged site (STS) markers for fine mapping of the barley (Hordeum vulgare) Ror1 gene required for broad-spectrum resistance to powdery mildew (Blumeria graminis f. sp. hordei). After locatingRor1 to the centromeric region of barley chromosome 1H using a combined amplified fragment length polymorphism/restriction fragment-length polymorphism (RFLP) approach, sequences of RFLP probes from this chromosome region of barley and corresponding genome regions from the related grass species oat (Avena spp.), wheat, and Triticum monococcum were used to develop STS markers. Primers based on the RFLP probe sequences were used to polymerase chain reaction-amplify and directly sequence homologous DNA stretches from each of four parents that were used for mapping. Over 28,000 bp from 22 markers were compared. In addition to one insertion/deletion of at least 2.0 kb, 79 small unique sequence polymorphisms were observed, including 65 single nucleotide substitutions, two dinucleotide substitutions, 11 insertion/deletions, and one 5-bp/10-bp exchange. The frequency of polymorphism between any two barley lines ranged from 0.9 to 3.0 kb, and was greatest for comparisons involving an Ethiopian landrace. Haplotype structure was observed in the marker sequences over distances of several hundred basepairs. Polymorphisms in 16 STSs were used to generate genetic markers, scored by restriction enzyme digestion or by direct sequencing. Over 2,300 segregants from three populations were used in Ror1 linkage analysis, mappingRor1 to a 0.2- to 0.5-cM marker interval. We discuss the implications of sequence haplotypes and STS markers for the generation of high-density maps in cereals.

Growth (length, weight) of yellow perch Perca flavescens in western and west-central Lake Erie began between June and July, possibly reaching asymptotic size by early winter. Energy density (kJ g−1) of somatic tissue increased markedly from June to September, then declined to low levels by the following spring. Consequently, energy mass (kJ) of somatic tissue increased to September and then declined slowly until March. Ovarian growth began in October, and the size of the ovaries was maximal in April, just before spawning in May. The energy density of ovaries, however, increased to a peak in December, and then declined. The increase in ovary size in the winter, therefore, resulted largely from an allocation of tissue of low energy density. Fecundity and gonad size were correlated with somatic and gonadal energy density. A bioenergetics model was used to describe the monthly allocations of energy to respiration, growth, excretion, and reproduction. Most direct reproductive costs (80%) were incurred from September to December, corresponding to the cycle in the activity of the liver. Energy acquired in the early summer may be critical for determining maturation, fecundity, and egg quality. From 1978 to 1990

A number of agronomically important grasses (sorghum, wheat, panicum, sugar cane, oats, rice and barley) are shown to contain sequences homologous to rp1, a maize gene that confers race-specific resistance to the rust fungus Puccinia sorghi. Mapping of rp1-related sequences in barley identified three unlinked loci on chromosomes 1HL, 3HL and 7HS. The locus located on chromosome 7HS comprises a small gene family of at least four members, two of which were isolated and are predicted to encode nucleotide binding site-leucine-rich repeat (NBS-LRR) proteins that are respectively 58% and 60% identical to the maize rp1 protein. Evidence of positive selection for sequence diversification acting upon these two barley genes was observed; however, diversifying selection was restricted to the carboxy terminal half of the LRR domain. One of these rp1 homologous genes cosegregated with the barley Rpg1 stem rust resistance gene amongst 148 members of the Steptoe × Morex double haploid mapping family. Three other unrelated resistance gene-like sequences, potentially encoding NBS-LRR proteins, are also shown to be linked to the Rpg1 locus but not cosegregating with the gene.

Habitat conditions may determine locations of patchily distributed small- mouth bass nests in lakes, since young smallmouth bass are fragile and are therefore vulnerable to suboptimal physical characteristics in their typically variable nesting area, the littoral zone. Knowing which habitat conditions are important to nest locations would ultimately be useful in protecting optimal nesting areas from anthropogenic disturbances in lakes. To evaluate factors related to the nest distributions of a smallmouth bass (Mi- cropterus dolomieui) population, physical habitat conditions were measured at 36 1-km- long and 31 100-m-long sites in Lake Opeongo (Ontario, Canada). Both tree regression analysis (a recently devised and unique statistical tool) and standard multiple regression were used to determine the relationships between nest density and four habitat variables. Tree regression analysis does not require assumptions of linearity or homoscedasticity of variances, and it automatically identifies interactions among variables. Furthermore tree regression results were more accurate and more precise than standard multiple-regression results. Mechanisms underlying the significant relationships between nest densities and both littoral zone temperatures and shoreline reticulation in 1-km-long sites and the non- significant results at the 100-m-long scale, are discussed. Cross-validation results quantify the difficulty in extrapolating sample findings to whole populations in ecological research.

Many of the plant disease resistance genes that have been isolated encode proteins with a putative nucleotide binding site and leucine-rich repeats (NBS-LRR resistance genes). Oligonucleotide primers based on conserved motifs in and around the NBS of known NBS-LRR resistance proteins were used to amplify sequences from maize genomic DNA by polymerase chain reaction (PCR). Eleven classes of non-cross-hybridizing sequences were obtained that had predicted products with high levels of amino acid identity to NBS-LRR resistance proteins. These maize resistance gene analogs (RGAs) and one RGA clone obtained previously from wheat were used as probes to map 20 restriction fragment length polymorphism (RFLP) loci in maize. Some RFLPs were shown to map to genomic regions containing virus and fungus resistance genes. Perfect co-segregation was observed between RGA loci and the rust resistance loci rp1 and rp3. The RGA probe associated with rp1 also detected deletion events in several rp1 mutants. These data strongly suggest that some of the RGA clones may hybridize to resistance genes.

The Yd2 gene in barley provides protection against barley yellow dwarf luteovirus (BYDV), the most economically devastating virus of cereals worldwide. Because resistance assays to identify Yd2-containing individuals from breeding populations are often difficult, we have developed a closely linked, codominant PCR-based marker for Yd2 using AFLP marker technology. The marker, designated YLM, can be amplified from barley genomic DNA prepared using a rapid and simple extraction procedure and, in a survey of more than 100 barley genotypes, was found to be polymorphic between most Yd2 and non-Yd2 lines. The YLM therefore shows excellent potential as a tool for selecting Yd2-carrying segregants in barley breeding programmes.

Smallmouth bass (Micropterus dolomieu) nests were patchily distributed within the littoral zone of Lake Opeongo at two spatial scales (1 km and 100 m shoreline segments). Nest locations were recorded by snorkelling along 155 and 6.3 km of littoral zone over 4 and 11 years, respectively. The degree of patchiness was greater and occurred more consistently at the 1-km than at the 100-m spatial scale. However, the degree of patchiness was not significantly affected by 200% differences in spawning population size, implying that competitive interactions did not strongly influence nest locations over the study period. High-density nesting areas remained stationary between years at the 1-km and 100-m scales. This suggests that habitat variables having stationary spatial characteristics, influence nest site choice. Since the locations of nest patches are less stationary and less consistent among 100-m than among 1-km scale sites, influential habitat variables at the 100-m scale are either less important to the locations of nests or less stationary from year-to-year in their effects on nest distributions. If stationary nest patches are typical of spawning smallmouth bass in lakes, permanent protection of known patch locations could enhance their reproductive success.

Barley yellow dwarf luteovirus (BYDV) causes serious yield losses in all cereals worldwide. The Yd2 gene from a number of Ethiopian barleys (Hordeum vulgare L.) has been the most effective means of providing resistance against BYDV in cultivated barley. Isolation of the Yd2 gene will enable characterisation of the molecular basis of the Yd2-BYDV interaction. This paper describes the first stage in a project to isolate the gene: the construction of a detailed linkage map of the Yd2 region. The map encompasses 27.6 centiMorgans (cM) of chromosome 3 and contains 19 RFLPs, 2 morphological marker loci, the centromere and Yd2. In the mapping population of 106 F2 individuals, Yd2 perfectly cosegregated with the RFLP loci Xwg889 and XYlp, which were located on the long arm, 0.5 cM from the centromere. The two morphological marker loci, uzu dwarfand white stripe j, both mapped distal to Yd2. The protein product of the gene at the XYlp locus will provide a convenient assay for the selection of Yd2 during the breeding of BYDV-resistant barley varieties.