Hordeum Jubatum Research Articles

Virulence phenotypes of Puccinia striiformis in Alberta from 2009–2011

One hundred and four isolates of Puccinia striiformis were obtained primarily from central Alberta during 2009–2011 from wheat, barley, foxtail barley and triticale. Isolates were identified as P. striiformis f. sp. tritici (Pst) or P. striiformis f. sp. hordei (Psh) based on virulence on differential seedlings. Twenty-five wheat differentials separated 67 Pst isolates into 12 pathotypes, with a single pathotype representing 48% of Pst isolates. Wheat differentials with resistance genes Yr5 and Yr15 were resistant to all 12 pathotypes, while wheat lines with genes Yr1, Yr10, Yr24, Yr28, YrTyee and YrSP were resistant to 80–98% of the isolates. The remainder of the wheat differentials were susceptible to all Pst isolates. Within the 37 Psh isolates, 12 pathotypes were detected based on 12 barley differentials, half of which were previously unreported in Alberta. The two most common Psh pathotypes combined accounted for 46% of the isolates. One half of the Psh isolates may be the result of hybridization between the two formae speciales since they exhibited virulence on a large number of wheat and triticale lines in addition to barley lines. Psh isolates with these virulence factors were more frequently recovered from six-row than two-row barley. For both formae speciales, there was no apparent association between pathotype and location, with pathotypes being widespread and recovered from multiple locations.

Expansion of invasive alien plant species in the republic of Bashkortostan, the Southern Urals: Analysis of causes and ecological consequences

The causes and ecological consequences of alien plant species invasions in the Southern Urals are analyzed. Aggressive invasive species of North American origin—Ambrosia trifida L., A. psylostachya DC., Cyclachaena xanthiifolia (Nutt.) Fresen., Hordeum jubatum L., Oenothera biennis L., Bidens frondosa L., etc.—have invaded synanthropic and natural plant communities and became dominant, with their proportion varying from 10 to 99%. The biomass of these plants may reach 6 kg/m2; density, more than 1000 shoots per square meter; and seed production, up to 30000 seeds per plant, which explains their dominance in communities. The ecological hazard they pose lies in the displacement of native species, overgrowing of disturbed land areas, and allergenicity of their pollen.

Salinity Tolerance of Foxtail Barley (Hordeum jubatum) and Desirable Pasture Grasses

Greenhouse studies were conducted to determine the relative salinity tolerance of foxtail barley and seven desirable pasture grasses. Grass species were reed canarygrass, timothy, altai wildrye, tall fescue, tall wheatgrass, orchardgrass, creeping meadow foxtail, and foxtail barley. Grasses were exposed to increasing electrical conductivity levels of NaCl and CaCl2 salt solution over time. Grass species were compared using a cumulative value of salt exposure (ECdays), which was calculated to account for the electrical conductivity (EC) and the time a plant was exposed at that level of conductivity. Salinity tolerance varied among grass species. Increasing EC significantly reduced plant biomass of all species. All grass species experienced a 50% biomass reduction (GR50) between 271 and 512 ECdays in 2008 and between 297 and 575 ECdays in 2009. Foxtail barley was among the most salt tolerant (GR50 = 512 and 525 ECdays), requiring the highest salt exposure in 2008 and the second-highest exposure in 2009 to reduce biomass 50%. Grass mortality increased with increasing EC levels. Reed canarygrass and timothy were most susceptible to increasing salinity, with 50% mortality (LD50) of both grass species occurring between 983 and 1,186 ECdays. Moderate salinity tolerance was exhibited by orchardgrass, which required 1,977 and 1,844 ECdays; creeping foxtail, which required 1,998 and 2,431 ECdays; and tall fescue, which required 2,501 and > 2,840 ECdays to LD50 in 2008 and 2009, respectively. Foxtail barley, altai wildrye, and tall wheatgrass were most tolerant of salinity and persisted with little mortality occurring at 3,033 and 2,840 ECdays in 2008 and 2009, respectively. All grass species with higher growth rates than foxtail barley and altai wildrye were more susceptible to salinity, with the exception of tall wheatgrass. Growth rates of foxtail barley and altai wildrye were less than they were for other grasses, suggesting that slower growth rates may aid in salinity tolerance.

Russian wheat aphid (Hemiptera: Aphididae) reproduction and development on five noncultivated grass hosts

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), is a small grains pest of worldwide economic importance. The Russian wheat aphid is polyphagous and may encounter differential selective pressures from noncultivated grass hosts. Aphid biotypic diversity can disrupt the progress of plant breeding programs, leading to a decreased ability to manage this pest. The goal of this research was to quantify Russian wheat aphid biotype 2 (RWA2) reproductive and development rates on five common noncultivated grass hosts to gain information about host quality, potential refuges, and sources of selection pressure. First, RWA2 reproduction was compared on crested wheatgrass (Agropyron cristatum, (L.) Gaertn.), intermediate wheatgrass (Elytrigia intermedia, (Host) Nevski), slender wheatgrass (Elymus trachycaulus, (Link) Gould ex Shinners), western wheatgrass (Pascopyrum smithi, (Rydb.) A. Love), and foxtail barley (Hordeum jubatum, (L.) Tesky) at 18–24°C. Second, RWA2 reproduction was compared on intermediate and crested wheatgrass at three temperature regimes 13–18°C, 18–24°C, and 24–29°C. At moderate temperatures (18–24°C), the intrinsic rate of increase values for all five hosts ranged from 0.141 to 0.199, indicating the possibility for strong population sources on all tested hosts. Aphids feeding on crested and intermediate wheatgrass at the 13–18°C temperature had lower fecundity, less nymph production days, longer generational times, and lower intrinsic rate of increase than aphids feeding at the 18–24°C temperature regime. Aphids feeding at 24–29°C did not survive long enough to reproduce. The positive intrinsic rates of increase in Russian wheat aphid on the wheatgrasses suggest that these grasses can support aphid populations at moderate to low temperatures.

Molecular phylogeny and reticulate origins of several American polyploid Hordeum species

The phylogeny of diploid species in the genus Hordeum has been studied intensively. Although the origin of American polyploid species has been analyzed using multiple-copy internal transcribed spacer sequences, the origins of these species in Hordeum remain unclear. The objectives of our study were to elucidate the origins of American polyploid species and to explore phylogenetic relationships of these polyploids to diploid Hordeum and other diploid species in Triticeae using a single copy of a nuclear gene, disrupted meiotic cDNA1 (DMC1). DMC1 sequences from nine Hordeum polyploid species were analyzed. Sequence comparisons revealed that one copy of sequences from polyploid species Hordeum fuegianum , Hordeum jubatum , and Hordeum tetraploidum showed a 82 bp miniature inverted-repeat terminal element (MITE) (Stowaway) insertion, which was also detected in the Triticeae diploid species Australopyrum species (W genome) and Taeniatherum caput-medusae (Ta genome). Maximum parsimony and Bayesian analysis suggested that diploid Hordeum brachyantherum subsp. californicum is one ancestor of polyploids Hordeum arizonicum , H. brachyantherum subsp. brachyantherum , Hordeum depressum , and Hordeum procerum . The other ancestor of tetraploid H. depressum is probably Hordeum euclaston . Hordeum cordobense was suggested to be one of the genome donors to hexaploid H. procerum. The diploid Hordeum flexuosum and tetraploid H. tetraploidum were suggested as the parents to hexaploid species Hordeum parodii . The result is that one sequence from each of three Hordeum tetrapolyploids, including H. fuegianum, H. jubatum, and H. tetraploidum, and one from Hordeum hexaploid H. arizonicum fall outside the Hordeum clade of the DMC1 phylogenetic tree, therefore representing another example of complex evolutionary history. Our data may shed light on future phylogenetic studies in Triticeae, especially for the polyploids, by broadening the scope of investigations through sampling more genome types in Poaceae, not only from the tribe Triticeae.

Pyroxasulfone with and without Sulfentrazone in Sunflower (Helianthus annuus)

Pyroxasulfone (KIH-485) is a seedling growth-inhibiting herbicide developed by Kumiai America that has the potential to control weeds in sunflower. However, little is known about how this herbicide will interact with various soil types and environments when combined with sulfentrazone. The objective of this research was to evaluate sunflower injury and weed control with pyroxasulfone applied with and without sulfentrazone across the Great Plains sunflower production area. A multisite study was initiated in spring 2007 to evaluate sunflower response to pyroxasulfone applied PRE at 0, 167, 208, or 333 g ai ha−1. In 2008, pyroxasulfone was applied alone and in tank mixture with sulfentrazone. In 2007, no sunflower injury was observed with any rate of pyroxasulfone at any location except Highmore, SD, where sunflower injury was 17%, 4 wk after treatment (WAT) with 333 g ha−1. In 2008, sunflower injury ranged from 0 to 4% for all treatments. Adding sulfentrazone did not increase injury. Sunflower yield was only reduced in treatments in which weeds were not effectively controlled. These treatments included the untreated control and pyroxasulfone at 167 g ha−1. Sunflower yield did not differ among the other treatments of pyroxasulfone or sulfentrazone applied alone or in combination. The addition of sulfentrazone to pyroxasulfone improved control of foxtail barley, prostrate pigweed, wild buckwheat, Palmer amaranth, and marshelder, but not large crabgrass or green foxtail. The combination of pyroxasulfone and sulfentrazone did not reduce control of any of the weeds evaluated.

Characterizing Pathways of Invasive Plant Spread to Alaska: II. Propagules from Imported Hay and Straw

AbstractThe extent and nature of spread of exotic plant species to and within Alaska by shipment of hay and straw was studied. The amounts of hay and straw imported into Alaska and the amounts and types of seed in imported and locally produced hay and straw was determined We purchased alfalfa hay, wheat straw, ryegrass straw, and timothy hay produced in Washington and Oregon (WA–OR) and locally produced straw and hay. The hay and straw were shaken over screens, and the remaining fines were mixed with sterile potting soil and incubated in the greenhouse. Forty-nine plant species were identified from hay and straw, nine of which are ranked as invasive in Alaska, including downy brome, foxtail barley, hare barley, narrowleaf hawksbeard, and quackgrass—a prohibited weed in Alaska. The number of seeds ranged from 0 to 6,205 seeds kg−1, with an average of 585 seeds kg−1, and the number of species ranged from 0 to 12, with an average of 4.2 species per bale. Crop seed comprised a large proportion of the germinated seeds in ryegrass straw, wheat straw, and timothy/brome hay (98, 78, and 62%, respectively), but was less prevalent (ranging from 0 to 38%) in the other three hay and straw crop types. Hay and straw from Alaska contained more total seeds and species than hay and straw from WA-OR, but the difference was not significant when only weed seed was used in the analysis. Alaska-grown timothy/brome hay contained significantly more total seed than alfalfa hay and wheat straw from WA–OR and Alaska-grown barley straw. The grower or distributor of the hay and straw also influenced the number of seeds and species among some crop types. Results of this study document that large numbers of alien plant species are transported by movements of hay and straw into and within Alaska.

Variation in Seed Viability and Dormancy of 17 Weed Species after 24.7 Years of Burial: The Concept of Buried Seed Safe Sites

A 50-yr study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2- and 15-cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, 19.7, and 24.7 yr later. Viability was determined using germination and tetrazolium tests. By 24.7 yr after burial (YAB), no viable seeds were found for common hempnettle, flixweed, foxtail barley, quackgrass, and wild oat. Bluejoint reedgrass, which had no live seed 19.7 YAB, again had viability (1% at 15 cm) 24.7 YAB. Seeds of 11 other species were still viable: American dragonhead (52%), marsh yellowcress (11 and 3.0% at 2 and 15 cm respectively), common lambsquarters (2.8%), prostrate knotweed (2.8% at 15 cm), shepherd's-purse (2.8%), pineapple-weed (2.6%), rough cinquefoil (2.3%), Pennsylvania smartweed (1.1%), common chickweed (0.4%), wild buckwheat (0.3%), and corn spurry (0.1%). Seed dormancy 24.7 YAB was very low (< 10%) for all species except American dragonhead (99%), shepherd's-purse (40%), marsh yellowcress (23% at 2 cm), Pennsylvania smartweed (18%), and rough cinquefoil (14%). At the beginning of the study, declines in seed longevity were uniform between replicates, but variability between replicates increased over time for all species except American dragonhead, suggesting that some soil microsites are more favorable for seed survival and may be seedbank “safe sites.” Results of this study demonstrate that nonrandom seed mortality contributes to the spatial heterogeneity of seed populations in the soil seedbank.

Alternative splicing and genetic diversity of the white collar-1 (wc-1) gene in cereal Phaeosphaeria pathogens

The white collar-1 (wc-1) gene encodes an important light-responsive protein (wc-1) that maintains circadian clocks and controls numerous light-dependent reactions including sporulation in ascomycete fungi. The structure and expression of the wc-1 gene in wheat-biotype Phaeosphaeria nodorum (PN-w) was studied. It was shown that the full-size (3,353 bp in length) wc-1 gene in PN-w contained 4 introns in which introns 1 and 2 were flanked by GC-AG splice borders and were spliced constitutively. However, introns 3 and 4 of the wc-1 gene were alternatively spliced. As the result of alternative splicing (AS), six transcript variants were identified, encoding different lengths of deduced polypeptides (from 1,044 to 1,065aa). Ratios of the wc-1 gene transcript variants in the RNA population were the same in the sporulated and non-sporulated PN-w isolate Sn37-1 and the sporulated PN-w isolate S-79-1, grown under light/dark conditions. The AS of the wc-1 gene may control various light-dependent reactions in PN-w, which leads to diverse morphological, physiological and pathological characters for pathogen infection and spread. Based on the nucleotide and deduced amino acid sequences, the wc-1 gene in cereal Phaeosphaeria pathogens was diverse. It appeared that the deduced wc-1 polypeptide sequences of P. avenaria f. sp. avenaria (Paa), P. avenaria f. sp. triticea (Pat1 and Pat3) and barley biotype P. nodorum (PN-b) were more closely related than PN-w and Phaeosphaeeria sp. (P-rye) from Poland. Based on the wc-1 deduced polypeptide sequences, P. avenaria f. sp. triticea (Pat2) from foxtail barley (Hordeum jubatum L.) was evolutionary well separated from the other cereal Phaeosphaeria pathogens.

Growing season energy and water exchange from an oil sands overburden reclamation soil cover, Fort McMurray, Alberta, Canada

AbstractThe oil sands mining industry in Canada is required to return mining areas to a land capability equivalent to that which existed prior to mining. During the reclamation process, ecosystems are created that bear little similarity to boreal forests that existed prior to mining. Quantifying the water balance of reclaimed ecosystems is critical in establishing whether there is sufficient moisture for vegetation growth and in the fate of salts, which can be toxic when drawn to the surface or leached out of the covers. At Syncrude Canada Ltd's Mildred Lake mine north of Fort McMurray, Alberta, the surface energy balance was measured atop a reclaimed saline‐sodic overburden pile during three growing seasons using eddy covariance. At the onset of the study, the dominant vegetation was foxtail barley, which changed to sweet clover in 2004, and a low‐density species mix in 2005, including some aspen and white spruce seedlings. The 2005 growing season was cooler and wetter than 2003 and 2004, and there were seasonal differences in the delivery of precipitation among years. There were distinct differences in the surface energy balance among the study years related to weather, soil moisture, vegetation and stage of growth. Latent heat was the largest consumer of energy in 2003, and mid‐day fluxes of sensible and latent heat were approximately equal. In 2004, sensible heat became the dominant flux, primarily due to prolonged dry periods, whereas the wet 2005 season had the greatest latent heat flux density of any year. Ground heat flux declined throughout the growing season and ranged between 3 and 17% of net radiation. Total evapotranspiration was 246, 224 and 283 mm for 2003, 2004 and 2005, respectively. A total derivative analysis of the Penman‐Monteith equation reveals the influence of available energy, vapour pressure deficit and surface conductance in controlling evapotranspiration. Copyright © 2008 John Wiley & Sons, Ltd.

Cytogenetics in hybrids of Hordeum jubatum and H. tetraploidum with cultivated barley (H. vulgare L.)

A crossing series between Hordeum vulgare and H. jubatum and H. tetraploidum was carried out. Five genotypes (varieties or lines] of the former species were used as pollen parents together with three accessions of H. jubatum and one accession of H. tetraploidum. There was a large genetic variation in compatibility in crosses among the barley genotypes. Selective chromosome elimination of the whole H. vulgare genome occurred in one hybrid in combination with H. jubatum. Elimination of individual barley chromosomes occurred in three cases. The meiotic pairing in hybrids and haploids agrees well with earlier results, i.e., there is probably no pairing between the H. vulgare chromosomes and those of the wild species. Homoeologous pairing in H. jubatum was generally low. except in two plants, whereas the homoeologous pairing among the H. tetraploidum chromosomes was considerably higher.

EFFECTS OF PRESCRIBED FALL BURNING ON A WETLAND PLANT COMMUNITY, WITH IMPLICATIONS FOR MANAGEMENT OF PLANTS AND HERBIVORES

An important contemporary challenge for adaptive resource management is assessing both the direct and indirect effects of management activities by designing appropriate monitoring programs and sound analysis meth- ods. Here we evaluate the effects of prescribed fall burning on a wetland plant community that is managed primarily for spring-migrating geese. During late fall in 2 consecutive years, we burned vegetation in 4 replicate blocks (2.3 ha each) that traversed a natural moisture and associated vegetation gradient. We used ordination, gradient analysis, and contin- gency table analysis to evaluate how annual changes in relative abundance of plants were affected by burning as well as other important ecological factors. Burning increased species diversity of plants, especially in the 2 wetter vegetation zones, but had no effect on species richness or on the proportion of native plant species. Wetland plant species responded to prescribed burning independently, and their response often differed by vegetation zone and with annual variation in flooding. Burning enhanced the abundance of native foxtail barley (Hordeum jubatum) and reduced the abundance of introduced swamp timothy (Crypsis shoenoides). Saltgrass (Distichlis spicata), a native plant species, was usually less abundant following burning, although the level of response was different for each of the 3 vegetation zones. Two other introduced plant species, quackgrass (Elytrigia repens) and reed canarygrass (Phalaris arundinaceae), were less abundant after fall burning, especially when spring flooding was more extensive. Wild geese using the experimental blocks for feeding clearly preferred burned sites, suggesting that fall burning can enhance wetland use by geese during spring. Given that simple manipulations such as burning and flooding of a wetland system may often produce complex results, we suggest that on-going management schemes be regularly evaluated with field experiments such as those con- ducted in this study.

Seed viability and dormancy of 17 weed species after 19.7 years of burial in Alaska

A study at Fairbanks, AK, was started in 1984 to determine soil seed longevity of 17 weed species. Seeds were buried in mesh bags 2 and 15 cm deep and were recovered 0.7, 1.7, 2.7, 3.7, 4.7, 6.7, 9.7, and 19.7 yr later. Viability was determined by germination and tetrazolium tests. Seed viability data were fit to an exponential model, separately for each depth, and the likelihood-ratio test was used to determine whether seed-viability decline was affected by burial depth. Depth of burial had a significant effect on viability decline of prostrate knotweed, marsh yellowcress, bluejoint reedgrass, and wild oat. By 19.7 years after burial (YAB), all seeds of common hempnettle, quackgrass, wild oat, foxtail barley, and bluejoint reedgrass were dead. Seeds of 12 other species were still viable: corn spurry (0.1%), prostrate knotweed (0.3% at 2 cm, 0.8% at 15 cm), flixweed (0.5%), pineapple-weed (0.6%), shepherd's-purse (1.3%), wild buckwheat (1.5%), common chickweed (1.6%), rough cinquefoil (1.8%), common lambsquarters (3.0%), Pennsylvania smartweed (3.3%), marsh yellowcress (8.5% at 2 cm, 0.3% at 15 cm), and American dragonhead (62.2%). Seed dormancy at 19.7 YAB was very low for all species (< 4%) except for American dragonhead, common lambsquarters, Pennsylvania smartweed, and shepherd's-purse, which had seed dormancies of 100, 27, 25, and 38%, respectively. Seed longevity was not increased by cold, subarctic temperatures.

Weed seed bank affected by tillage intensity for barley in Alaska

The weed seed bank of a long-term tillage study in subarctic Alaska was studied at the end of 10 years of continuous spring barley ( Hordeum vulgare L.). Tillage treatments were: no-till, disked once (spring), disked twice (spring and fall), and chisel plow (fall). Soil cores were obtained from each tillage treatment and seeds were manually separated from soil after washing through sieves. Tillage treatment had a significant effect on seed density of shepherds purse ( Capsella bursa-pastoris (L.) Medic.), cinquefoil ( Potentilla norvegica L.), foxtail barley ( Hordeum jubatum L.), and on total seed density. Seed density was higher for these species and total seed density was greater under no-till than under other tillage treatments. Seed density was higher near the soil surface under no-till and chisel plow treatments than under disked treatments, which helps explain the greater difficulty of controlling weeds under reduced tillage.

Presence of β-glucosidase (bgl1) gene in Phaeosphaeria nodorum and Phaeosphaeria avenaria f.sp. triticea

Phaeosphaeria avenaria f.sp. avenaria (Paa), the causal agent of stagonospora leaf blotch in oats, produces a glycosyl hydrolase family 3 enzyme, β-glucosidase, which is responsible for detoxification of steroidal avenacosides in oat leaves, but is not essential for pathogenicity. For a comparative genetic relatedness study, a Paa-like β-glucosidase gene (bgl1) was PCR-amplified from Phaeosphaeria nodorum and P. avenaria f.sp. triticea, and Phaeosphaeria spp. from dallis grass (Paspalum dilatatum) (isolate S-93-48) and rye (Secale cereale) (isolate Sn48-1). Different sizes of bgl1 gene coding sequences ranging from 3018 to 3023 bp were determined. The bgl1 gene structure in these Phaeosphaeria species was identical to that of Paa and contained four exons and three introns. Nucleotide variations occurring in introns 1 and 2 of the bgl1 gene divided wheat-biotype P. nodorum into four groups. Two 12-bp-long direct sequence repeats (5'-TCA/G ACT GGT TT/CA/G) were found in the promoter region of the bgl1 gene in Phaeosphaeria species; only one repeat was present in the two P. avenaria f.sp. triticea isolates ATCC26370 and ATCC26377 (Pat2) from foxtail barley (Hordeum jubatum) and some homothallic P. avenaria f.sp. triticea isolates (Pat1). With sequence similarities in the noncoding internal transcribed spacer region of nuclear rDNA, the partial gpd gene fragment containing the intron 4, and the full-length bgl1 gene, five Phaeosphaeria isolates (5413, 1919WRS, 1920WRS, 1921WRS, Sa37-2) from oat (Avena sativa) were molecularly determined to be Paa. Two oat isolates (Sa38-1 and Sa39-2) from Poland appeared to be Pat1. The results suggest that classification of two Phaeosphaeria avenaria formae speciales based on host specificity should be re-evaluated.Key words: wheat, oat, Phaeosphaeria, β-glucosidase gene.

Sequence diversity of β-tubulin ( tubA) gene in Phaeosphaeria nodorum and P. avenaria

Full-length coding sequences of the β-tubulin gene ( tubA) were PCR-amplified and sequenced from 42 Phaeosphaeria isolates, including 16 P. nodorum and 23 P. avenaria species from cereals, two Polish isolates from rye ( Secale cereale L.), and one isolate from dallis grass ( Paspalum dilatatum Poir). A tubA gene of size 1556 bp was identified in wheat- and barley-biotype P. nodorum (PN-w and PN-b), P. avenaria f. sp. avenaria (Paa), homothallic P. avenaria f. sp. triticea ( P. a. t.) (Pat1) and the P. a. t. isolate (Pat3) from the State of Washington. The tubA gene length polymorphisms were detected in two P. a. t. isolates (Pat2) from foxtail barley ( Hordeum jubatum L.), one from dallis grass and two Polish isolates from rye. These size differences were due to the variation of intron lengths among these three Phaeosphaeria species. All Phaeosphaeria isolates have identical 1344 bp exons that can be translated into a 447 amino acid β-tubulin. Like glyceraldehyde-3-phosphate dehydrogenase, the β-tubulin amino acid sequence was identical in all Phaeosphaeria species used in this study, with the exception of the two Pat2 isolates. Six amino acid differences were evident in the β-tubulin of these Pat2 isolates.

Seed germination of common weed species as affected by oxygen concentration, light, and osmotic potential

Laboratory experiments were conducted to determine the effects of oxygen concentration (21, 10, 5, and 2.5%), exposure to light, and osmotic potential on the germination of wheat, canola, and various weed species. Germination of most species increased as osmotic potential was increased. Seed germination for some species like barnyardgrass was inhibited by the combination of exposure to normoxic (21% oxygen) conditions and light. This combination of conditions may function as a signal to prevent soil surface germination. Wild mustard germination increased with increasing oxygen concentration when seeds were not exposed to light, whereas green foxtail germination was relatively insensitive to oxygen concentration. Wild oat germination increased with increasing osmotic potential, and osmotic potential had a greater influence when the seeds were exposed to light. Dandelion, foxtail barley, curly dock, and perennial sowthistle germination was affected more by osmotic potential and light exposure than by oxygen concentration. A better understanding of the mechanisms of depth detection for specific species will lead to a better understanding of their recruitment biology. This information may help model the potential for invasion and proliferation of each species as well as devise improved management strategies.

Physiologic specialization of Puccinia graminis on wheat, barley, and oat in Canada in 2000

Stem rust is a devastating disease of cereal crops that is currently controlled, in Canada, primarily through the use of resistant cultivars. Annual surveys are conducted throughout Canada to monitor rust severity and obtain rust collections that are used to determine the virulence spectrum of each pathogen population. This is necessary for the detection of novel races that may express high virulence to currently grown cereal cultivars and to identify changes in virulence in the pathogen population. No stem rust was observed on cultivated spring wheat in 2000. Stem rust severity was light (<5%) on barley and oat in Manitoba, eastern Saskatchewan, and Ontario in 2000 and stem rust was not detected in other regions. Stem rust samples were collected from Hordeum jubatum, Avena fatua, and trap-plot nurseries and commercial fields of wheat, barley, and oat in Manitoba, eastern Saskatchewan, and Ontario from June to September 2000. Eight races of Puccinia graminis f. sp. tritici were found in collections from wheat, 11 from cultivated barley, and 2 from wild barley, with RCRSK as the dominant race on all three hosts. However, a cluster of races (QCCJ_, RCCJ_, and RMCJ_) with virulence to cultivated barley composed 69.2% of the population in Manitoba and Saskatchewan and poses a threat to barley production in this region. Five races of P. graminis f. sp. avenae were found in collections from cultivated oat and six from wild oat. Races NA67 and NA29 were the most common on cultivated (52.2 and 30.4%, respectively) and wild (18.6 and 55.0%, respectively) oat, while NA76 increased in frequency (9.6%) in Manitoba and Saskatchewan in 2000. Races NA67 and NA76 are virulent to Pg2, Pg9, and Pg13, which are the resistance genes likely present in most currently grown Canadian oat cultivars, and threaten commercial oat production in this region.

Differential effects of salinity on leaf elongation kinetics of three grass species

This study focuses on the inhibitory effect of salinity on the leaf extension of three different grass species: Hordeum jubatum L., Hordeum vulgare L. and Zea mays L. Leaf elongation rates (LER) were measured on the third leaf of the plants. NaCl was added to the hydroponic solution (0, 40, 80 and 120 mM) and changes in LER were measured over time with a displacement transducer. Salinity inhibited LER immediately in all three species, and a new, but lower steady-state LER was reached within 5 h. The decrease in LER was proportional to the salinity level. Differences in salt tolerance (% of control LER) were evident between genotypes within 5 h after salinization, but the relative salt tolerance of the plant at this stage was not necessarily indicative of the long-term salt tolerance of the species. In general, H. jubatum was more tolerant than maize, which was more tolerant than barley to these short-term salinity stresses. In contrast, barley is more salt tolerant than maize over the long term. The mechanisms of inhibition of LER by salinity, as tested by the applied-tension technique, varied with the species examined, affecting either the apparent yield threshold, the hydraulic conductance of the whole plant or both. The cell wall extensibility was not significantly affected by salinity in the three species tested in this study.

Molecular phylogeny of the genus Hordeum using three chloroplast DNA sequences.

The genus Hordeum consists of three cytotypes (2x, 4x, and 6x). Its reproductive isolation has been incomplete between closely related species and hence the genetic relationship is reticulate and complex. We used 32 taxa of Hordeum and three chloroplast DNA sequences, matK, atpB-rbcL, and trnL-trnF in the current study. Molecular phylogenetic analysis based on sequence data of the three chloroplast DNA regions clearly demonstrated genetic relationships among taxa and origin of polypoids. The formation of H. secalinum likely involved hybridization between Hordeum marinum subsp. marinum and a Eurasian diploid possessing the H genome. The formation of hexaploid Hordeum brachyantherum involved hybridization between tetraploid H. brachyantherum and diploid H. marinum subsp. gussoneanum. The formation of three tetraploids, H. brachyantherum, Hordeum jubatum, and Hordeum guatemalense, probably involved hybridization between H. brachyantherum subsp. californicum and an altered H genome diploid. The formation of Hordeum arizonicum involved the two taxa Hordeum pusillum and H. jubatum.