Regional Plant Introduction Station Research Articles

Seed germination of four amaranth species (Amaranthus spp.)

Amaranthus (Amaranthus spp.) is a species of great importance that benefits human and animal nutrition; therefore, its reproduction must be based on useful information obtained from rigorous experiments. Consequently, the aim of this work was to determine the germination of 20 accessions from four Amaranthus spp. The work was carried out at the Instituto Tecnológico de Chiná, Campeche, Mexico, using seeds from Africa, Asia, Greece, South America, the US, and Mexico, donated by The North Central Regional Plant Introduction Station (NCRPIS), Iowa State University. After they were weighed and measured, the seeds were placed in Petri dishes and kept in the dark inside a germination chamber, at 27 ºC and with a 54% relative humidity. Germinated seeds were counted and removed every 24 hours. The analyses were carried out using the ANOVA test in order to identify weight, length, and germination differences between accessions. The results showed no statistical differences in seed length, neither between species nor accessions; however, there were statistical differences in the weight, both between species and between accessions. A. hypochondriacus from India recorded the highest weight (0.00093 ± 0.000075 g). Regarding germination, there were statistical differences between the various evaluation periods (24 and 48 hours): the highest germination was recorded by A. hypochondriacus and A cruentus. Therefore, the following conclusion was reached: seed germination is different between species and accessions.

Fifty years of collecting wild Helianthus species for cultivated sunflower improvement

Abstract Wild Helianthus species have been undeniably beneficial in sustaining the sunflower crop by providing plant breeders with a diverse genetic pool of potentially useful traits. Exploration to collect populations of wild sunflowers is one of the more difficult and challenging activities in the conservation and utilization of these valuable genetic resources. The logistics of collecting requires careful planning, locating the target species, obtaining permission to access and collect, and timing the exploration to ensure the availability of mature seed. The US Department of Agriculture, Agricultural Research Service (USDA-ARS) established the wild Helianthus seed collection in 1976 at Bushland, Texas with the goal of collecting and conserving the broadest representative genetic diversity possible and serving as a central repository of germplasm and related information. In 1985 this collection was transferred to UDSA-ARS, North Central Regional Plant Introduction Station, Ames, Iowa. Over the last half century, 37 explorations were undertaken covering 175,000 km to collect the 53 Helianthus species from their distributional ranges in the forty-eight conterminous states in the US, three Canadian Providences (Manitoba, Saskatchewan, and Alberta), Argentina and Australia. The many explorations have created a global crop wild relatives (CWR) genebank collection. The current wild CWR sunflower genebank contains 2562 accessions of 53 species with 1065 wild Helianthus annuus accessions (42 %), 617 accessions representing populations of the 13 other wild annual species (24 %), and 880 accessions representing 39 perennial species (34 %). This collection is the largest and most genetically diverse ex situ sunflower collection in the world and is vital to the conservation of wild sunflower species for the global sunflower community.

Using public databases for genomic prediction of tropical maize lines

AbstractIn this paper, the aims were (a) to test the usefulness of using genomic and phenotypic information from public databases (open access) to predict genetic values for tropical maize inbred lines regarding plant and ear height; (b) to identify how the population structure, the use of optimized training sets (OTSs) and the amount of information originating from public databases affect the predictive ability. Thus, 29 training sets (TSs) were defined considering three diversity panels: the University of São Paulo (USP—validation set (VS)) and the ASSO and USDA North Central Regional Plant Introduction Station (NCRPIS) (external public panels—predictors), which were divided into four scenarios with different TS configurations. We showed that it is possible to use public datasets as a primary TS and that population structure can modify the predictive abilities of GS. In the four scenarios proposed, very large or very small sets did not provide predictive abilities over 0.53 for GS. However, OTSs composed of 250 individuals were sufficient to achieve predictive abilities over this limit.

Is the USDA core collection of common bean representative of genetic diversity of the species, as assessed by SNP diversity?

AbstractCore collections are envisioned to be a representative subset of larger germplasm collections. They were introduced to facilitate the characterization and use of these germplasm collections. The common bean (Phaseolus vulgaris L.) core collection of the USDA Western Regional Plant Introduction Station was one of the first collections to be established in the early 1990s. Here, we evaluate the representativity of this common bean collection in light of the availability of a single nucleotide polymorphism (SNP) platform and new information about genetic diversity of the species, including phaseolin and seed type data. The SNP diversity was studied with a combination of STRUCTURE, principal coordinate analysis (PCoA), and neighbor‐joining analysis (NJA). STRUCTURE analyses were conducted for K (number of subpopulations) = 3 and K = 7, based on the ad hoc statistic ΔK. The K = 3 analysis recognized the split between Andean and Mesoamerican domesticates and the subdivision of the Mesoamerican domesticates into high‐ (Durango/Jalisco) and low‐altitude (Mesoamerica) ecogeographic races. The K = 7 analysis further subdivided the Andean group identified for K = 3, as well as the high‐altitude group from the Mesoamerican gene pool. It also identified smaller groups consisting of Mesoamerican wild beans. The PCoA and NJA confirmed the STRUCTURE results and highlighted the existence of presumed hybridization among groups. Our results suggest that this core collection should be updated by adding domesticated categories, developing a separate wild common bean core collection, and developing cores for specific purposes.

Conserving Crop Diversity: Connecting Agriculture, Public Gardens, and Science

Conserving Crop Diversity: Connecting Agriculture, Public Gardens, and Science

Registration of Four Winter-Hardy Faba Bean Germplasm Lines for Use in Winter Pulse and Cover Crop Development

Faba bean (Vicia faba L.) is a versatile crop grown for food, feed, vegetable, or cover crop purposes in many countries. In response to the growing demand for winter annual legumes for cover crop development in the United States, we developed four winter-hardy faba bean germplasm lines, WH-1 (Reg. No. GP-3, PI 674326), WH-2 (Reg. No. GP-4, PI 674327), WH-3 (Reg. No. GP-5, PI 674328), and WH-4 (Reg. No. GP-6, PI 674329) at the USDA-ARS, Western Regional Plant Introduction Station, Pullman, WA, after six consecutive seasons of overwintering selection at three farms in two locations; Pullman and Central Ferry, WA. These four accessions were identified after the initial screening of 175 accessions from the USDA faba bean germplasm during the 2008–2009 and 2009–2010 winter seasons. In the following years, these populations were compared with several winter-type cultivars and breeding lines from Europe. During the final testing season, in 2013–2014, selected and original accessions were compared. The average increase in percentage survival was 84% across the four accessions. Furthermore, the winter hardiness of the selected accessions was comparable to European materials. These four lines are potential reservoirs of useful diversity accessible for the development of a winter annual legume cover crop in the U.S. Pacific Northwest and other regions up to USDA plant hardiness zone 6b.

Variability of Resistance to Cletus fuscescens Walker (Coreidae: heteroptera) in Grain Amaranth Germplasm

The level of resistance to insect pests in cultivated amaranth (Amaranthus cruentus L) is low. Twenty-nine accessions of amaranth germplasm, from diverse origins, obtained from the North Central Regional Plant Introduction Station of the United States National Plant Germplasm System were evaluated for 15 qualitative and eight quantitative traits at the National Horticultural Research Institute, Ibadan, Nigeria, to assess variability of tolerance to Cletus fuscescens Walker (Coreidae: Heteroptera). Quantitative traits were analyzed for cluster and principal component (PC) analysis. Variation was observed in the qualitatively inherited traits studied. High variability among accessions occurred in the quantitative traits viability percentage, grain yield/plant, and plant height. Principal component analysis indicated that the first three PCs with eigenvalues >1 explained 80.80% of variability among accessions. The variance explained by PC1 was due to the variation in C. fuscescens infestation and seed viability percentage; that of PC2 was due to 1000 seed weight and grain yield/plant. Cluster analysis grouped the germplasm into three clusters. Cluster I consisted of accessions with highest C. fuscescens infestation, least seed viability percentage, and highest seed yield. Cluster II consisted of accessions with high C. fuscescens, low seed viability percentage, and least seed yield, and cluster III consisted of accessions with least C. fuscescens infestation, highest seed viability percentage, and high seed yield. The clustering pattern indicated a strong association between C. fuscescens infestation and seed viability. The germplasm exhibited variability of resistance to C. fuscescens infestation along with accessions with unique seed viability percentage and seed yield that could be explored to develop high yielding grain amaranth varieties with resistance to C. fuscescens.

Target region amplification polymorphism (TRAP) for assessing genetic diversity and marker-trait associations in chickpea (Cicer arietinum L.) germplasm

The effective utilization of crop diversity held in genebanks depends on our knowledge of useful traits and available markers associated with the target traits. Target region amplification polymorphism (TRAP) was used to evaluate the genetic diversity and underlying relationships among 263 accessions of chickpea landraces maintained by the USDA-ARS Western Regional Plant Introduction Station in Pullman, WA, USA. Two-hundred sixty-two TRAP markers were amplified by eight primer combinations. Altogether, 110 (42 %) markers were polymorphic, the other 152 (58 %) displayed no variation. These polymorphic markers revealed important differences among the accessions, with an estimated, mean pair-wise genetic distance of 25.82 %, ranging from 2.8 to 50.0 %. Genetic distance analysis divided the accessions into two major groups, with 113 and 150 accessions each, and substantial association between molecular diversity and geographic origin was evident. Bayesian analysis of population structure revealed two groups (K = 2) with evidence for six sub-groups. Additionally, the population structure of a subset of 110 lines was determined (K = 3) for testing marker-trait associations (MTAs). Phenotypic traits included the concentrations of protein and nine mineral elements in the seeds. Two MTAs were significant (p < 0.01) for concentrations of Ca and K, and three MTAs were significant for Cu and Ni concentrations. The results indicate that this population is useful for genome-wide association studies on other economic traits given the level of genetic diversity uncovered and the marker-trait associations in seed minerals discovered.

The Genetic Architecture of Maize Stalk Strength

Stalk strength is an important trait in maize (Zea mays L.). Strong stalks reduce lodging and maximize harvestable yield. Studies show rind penetrometer resistance (RPR), or the force required to pierce a stalk rind with a spike, is a valid approximation of strength. We measured RPR across 4,692 recombinant inbreds (RILs) comprising the maize nested association mapping (NAM) panel derived from crosses of diverse inbreds to the inbred, B73. An intermated B73×Mo17 family (IBM) of 196 RILs and a panel of 2,453 diverse inbreds from the North Central Regional Plant Introduction Station (NCRPIS) were also evaluated. We measured RPR in three environments. Family-nested QTL were identified by joint-linkage mapping in the NAM panel. We also performed a genome-wide association study (GWAS) and genomic best linear unbiased prediction (GBLUP) in each panel. Broad sense heritability computed on a line means basis was low for RPR. Only 8 of 26 families had a heritability above 0.20. The NCRPIS diversity panel had a heritability of 0.54. Across NAM and IBM families, 18 family-nested QTL and 141 significant GWAS associations were identified for RPR. Numerous weak associations were also found in the NCRPIS diversity panel. However, few were linked to loci involved in phenylpropanoid and cellulose synthesis or vegetative phase transition. Using an identity-by-state (IBS) relationship matrix estimated from 1.6 million single nucleotide polymorphisms (SNPs) and RPR measures from 20% of the NAM panel, genomic prediction by GBLUP explained 64±2% of variation in the remaining RILs. In the NCRPIS diversity panel, an IBS matrix estimated from 681,257 SNPs and RPR measures from 20% of the panel explained 33±3% of variation in the remaining inbreds. These results indicate the high genetic complexity of stalk strength and the potential for genomic prediction to hasten its improvement.

Mycobiota of &lt;em&gt;Lupinus albus&lt;/em&gt; seeds from a public germplasm collection

Seedborne mycobiota of Lupinus albus was assessed using blotter paper and agar media with Rose Bengal or semi-selective media for Pythium or Fusarium . Samples of 200 seeds were taken from each of 16 inventories, comprising 14 accessions originating from Germany, France, Ukraine, Syria, Hungary or Spain, and increased 1-2 times through propagation by the USDA-ARS Western Regional Plant Introduction Station. A total of 307 fungus isolates were recovered and preserved with over 96% belonging to 10 genera: Penicillium (47%), Cladosporium (32%, including Cladosporium -like Chalastospora ) , Alternaria (4%), Aspergillus (4%), Fusarium (3%), Rhizopus (3%) , Ulocladium (3%), Chaetomium (0.5%) and Arthrinium (&lt; 0.5%). By sub-sampling, fungi were further identified by morpho-cultural characters and/or DNA sequences as Alternaria infectoria , A. alternata, and A. tenuissima species-groups, Arthrinium arundinus , Aspergillus niger , Chalastospora gossypii , Cladosporium herbarum and C. cladosporioides species complexes, Chaetomium sp., Fusarium acuminatum , Rhizopus stolonifer , and Ulocladium atrum group. Penicillia included P. hordei , but most Penicillia could not be assigned species names either by morphological traits or β-tubulin DNA sequence data.

Screening for Resistance to Verticillium Wilt in Spinach and Isolation of Verticillium dahliae from Seed of Spinach Accessions

Verticillium dahliae is a pathogen of spinach (Spinacia oleracea) during spinach seed crop production but not in vegetative leafy spinach crops, because plants remain asymptomatic until bolting has been initiated (conversion from vegetative to reproductive growth). The objectives of this research were to evaluate a set of USDA spinach germplasm accessions for resistance to Verticillium wilt and to determine the range in incidence of natural seed infection/infestation in a subset of the USDA spinach accessions screened for resistance. A total of 120 Spinacia spp. accessions from the USDA North Central Regional Plant Introduction Station spinach germplasm collection and 10 commercial S. oleracea hybrids were screened for resistance to V. dahliae in Trials 1, 2, and 3 in 2006, 2007, and 2008, respectively, in greenhouse evaluations. Each accession was grown in either V. dahliae-infested or non-infested potting mix and rated weekly on a seven-step scale from 1 week before bolting to 4 weeks after bolting. A wide range of disease severity ratings was observed among the accessions evaluated. Most of the accessions were highly susceptible. There was no evidence of qualitative resistance but some showed greater levels of quantitative resistance than others. Plants in soil infested with V. dahliae senesced faster and had significantly reduced biomass compared with plants in non-infested soil of the same accession. In addition, in Trial 2 (2007), 34% (20 of 59) of the seed samples assayed of the accessions were infested or infected with V. dahliae; and in Trial 3, (2008) 16% (21 of 130) of the seed samples of the USDA accessions evaluated were infested or infected with V. dahliae, V. tricorpus, or Gibellulopsis nigrescens (formerly known as V. nigrescens). These results are valuable for characterizing potential genetic variability within spinach germplasm for resistance to V. dahliae.

Effects of chemically characterized fractions from aerial parts of Echinacea purpurea and E. angustifolia on myelopoiesis in rats.

Echinacea species are used for beneficial effects on immune function, and various prevalent phytochemicals have immunomodulatory effects. Using a commercial E. purpurea (L.) Moench product, we have evaluated the myelopoietic effect on bone marrow of rats treated with various extracts and correlated this with their chemical class composition. Granulocyte/macrophage-colony forming cells (GM-CFCs) from femurs of female Sprague-Dawley rats were assessed at 24 h after 7 daily oral treatments. A 75% ethanolic extract at 50 mg dried weight (derived from 227 mg aerial parts) per kg body weight increased GM-CFCs by 70% but at 100 mg/kg was without effect. Ethanolic extracts from aerial parts of E. angustifolia DC. var. angustifolia and E. purpurea from the USDA North Central Regional Plant Introduction Station increased GM-CFCs by 3- and 2-fold, respectively, at 200 mg/kg (~1400 mg/kg plant material). Extract from another USDA E. angustifolia was inactive. Proton and APT NMR, MS, and TLC indicated alkylamides and caffeic-acid derivatives (CADs) present in ethanolic extracts of both the commercial and USDA-derived material. Cichoric and caftaric acids were prominent in both E. purpurea ethanolic extracts but absent in E. angustifolia. Aqueous extract of the commercial material exhibited polysaccharide and CAD signatures and was without effect on GM-CFCs. A methanol-CHCl3 fraction of commercial source, also inactive, was almost exclusively 1:4 nonanoic: decanoic acids, which were also abundant in commercial ethanolic extract but absent from USDA material. In conclusion, we have demonstrated an ethanolextractable myelostimulatory activity in Echinacea aerial parts that, when obtained from commercial herbal supplements, may be antagonized by medium-chain fatty acids presumably derived from a non-plant additive.

Genetic Diversity of a Maize Association Population with Restricted Phenology

Association analysis to identify genes and alleles underlying quantitative genetic variation is growing in value as the density of genotypic data increases. Association panels are often chosen to maximize molecular and phenotypic diversity, but traits measured at harvest require restricted phenology to obtain data on plants that mature within a comparable interval. The objective of this study was to characterize a set of inbred lines that will mature reliably in the upper midwestern United States for the purpose of assessing traits relevant to grain and stover yield as well as stover quality. A total of 1411 lines from the North Central Regional Plant Introduction Station, our program, and contributed by collaborators were grown in observation plots. A set of 627 lines were chosen based on flowering within the desired interval, production of viable seed, agronomic suitability, uniformity, and pedigree information. Flowering time ranged from 944 to 1645 growing degree days (GDD). Genotypic data for the 627 lines was obtained using a 1536 Illumina GoldenGate assay. The panel offers deep replication of most Midwest dent alleles. There is a lesser representation of tropical alleles relative to other association panels but includes some Germplasm Enhancement of Maize (GEM)‐derived lines and early flowering lines of tropical origin. The information described in this manuscript is anticipated to facilitate the use of this material for association genetic studies.

Germplasm resources for increasing the genetic diversity of global cultivated sunflower

Genebanks are a rich source of genetic diversity that can be readily exploited for crop improvement. The USDA-ARS established a cultivated sunflower germplasm collection at the National Plant Germplasm System, North Central Regional Plant Introduction Station at Ames, Iowa in1948. A wild Helianthus germplasm collection was established at the USDA-ARS Bushland, Texas station in 1976. Presently, both collections are maintained and managed at Ames, Iowa. The genus Helianthus consists of 52 species and 19 subspecies, with 14 annual and 38 perennial species. Over 30 explorations in the past 35 years have resulted in the assemblage of a wild sunflower collection that is the most complete in the world. Currently, the sunflower collections contain 4087 accessions: 1886 cultivated H. annuus accessions and 2201 wild accessions of which 1359 accessions are annual and 842 are perennial species. This germplasm is an important current and future genetic resource to combat emerging pests and environmental challenges, helping to maintain sunflower as a viable major global oilseed crop and preserve it for future generations.

Hypericum in infection: Identification of anti-viral and anti-inflammatory constituents

The Iowa Center for Research on Botanical Dietary Supplements seeks to optimize Echinacea, Hypericum, and Prunella botanical supplements for human-health benefit, emphasizing anti-viral, anti-inflammatory, and anti-pain activities. This mini-review reports on ongoing studies on Hypericum. The Center uses the genetically diverse, well-documented Hypericum populations collected and maintained at the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), and the strength of research in synthetic chemistry at Iowa State University to tap natural diversity, to help discover key constituents and interactions among constituents that impact bioactivity and toxicity. The NCRPIS has acquired more than 180 distinct populations of Hypericum, with a focus on Hypericum perforatum L. (Hypericaceae), representing about 13% of currently recognized taxa. Center chemists have developed novel synthetic pathways for key flavones, acyl phloroglucinols, hyperolactones, and a tetralin that have been found in Hypericum, and these compounds are used as standards and for bioactivity studies. Both light-dependent and light-independent anti-viral activities have been identified by using bioactivity-guided fractionation of H. perforatum and a HIV-1 infection test system. Our Center has focused on light-independent activity, potentially due to novel chemicals, and polar fractions are undergoing further fractionation. Anti-inflammatory activity has been found to be light-independent, and fractionation of a flavonoid-rich extract revealed four compounds (amentoflavone, chlorogenic acid, pseudohypericin, and quercetin) that interacted in the light to inhibit lipopolysaccharide-induced prostaglandin E2 activity. The Center continues to explore novel populations of H. perforatum and related species to identify constituents and interactions of constituents that contribute to potential health benefits related to infection.

Evaluation of USDA Lupinus sp. collection for seed-borne potyviruses

Plant viruses pose a threat to the acquisition, maintenance and distribution of lupin germplasm (genusLupinus, familyFabaceae). The availability of sufficient quantities of healthy and virus-free seeds from maintained lupin collections is mandatory for conducting lupin research. The objective of this research was to determine which lupin species were potentially infected with potyviruses (presumably seed-borne) upon germination in the greenhouse. The procedure for screening lupin seedlings in the greenhouse for potyviruses incorporated enzyme-linked immunosorbent assay followed by elimination or segregation of infected seedlings from the population before transplantation into the field plots for regeneration and accession characterization. None of the accessions in this evaluation had been tested previously for virus. From 2002 to 2005, 15 perennial (30 accessions) and 6 annual lupin species (213 accessions) were evaluated on site at the Western Regional Plant Introduction Station in Pullman, WA, USA. While none of the greenhouse perennial seedlings tested positive for potyvirus, seedlings in three annual species (Lupinus albus,Lupinus angustifoliusandLupinus luteus) were infected by potyviruses, presumably by seed transmission. Future testing may focus on the annual species, thus saving limited germplasm maintenance resources.

First Report of Bean yellow mosaic virus from Diseased Lupinus luteus in Eastern Washington.

Lupine accessions from the Cool Season Food Legume Seed Collection are grown for seed regenerations in Pullman, WA by the Agricultural Research Service, Western Regional Plant Introduction Station. Selected seed was germinated in the greenhouse and assayed by indirect ELISA using antiserum for potyvirus group detection (Agdia, Inc., Elkhart, IN). Healthy transplants were grown for seed collection on outside plots. In July of 2005, more than 90% of 307 Lupinus luteus L. transplants developed severe yellowing, necrosis, and stunting with an estimated 5% plant death. Plants were heavily infested with aphids and leaf sap was serologically positive for potyvirus. Partially purified virus preparations from infected plants contained filamentous particles and a 35-kDa protein that reacted with universal potyvirus antiserum on western blots. Reverse transcription (RT)-PCR using potyvirus universal primers (2) and cDNA derived from virion RNA generated a ~1.7-kbp product that was cloned and sequenced. The sequenced portion of the genomic RNA contained 1,610 nucleotides (nt) on its 3'-terminus (GenBank Accession No. EU144223) that included a partial nuclear inclusion protein, NIb, (1 to 637 nt) with the conserved amino acid (aa) replicase motif GDD (131 to 139 nt), the coat protein (CP) gene of 821 nt (638 to 1,459 nt), and a 171-nt untranslated region (1,460 to 1,630 nt) attached to a poly(A)tail. The CP sequence contained a NAG motif instead of the DAG motif commonly associated with aphid transmission. Searches in the NCBI GenBank database revealed that the CP aa and nt sequences contained conserved domains with isolates of Bean yellow mosaic virus (BYMV). A pairwise alignment (ClustalX) (4) of the CP aa from 20 BYMV isolates with the BYMV-Pullman isolate revealed identities from 96% (BYMV-S, U47033) to 88% (BYMV-MI [X81124)] -MI-NAT [AF434661]). This meets the species demarcation criteria of more than ~80% identity for inclusion with BYMV (1). Virion mechanical inoculations resulted in local lesions on Chenopodium amaranticolor Coste et Reyn and C. quinoa Willd., necrotic blotches on Phaseolus vulgaris L., and yellow spots and systemic movement in L. succulentus Douglas ex. K. Koch, L. texensis 'Bluebonnet', and L. texensis 'Maroon'; BYMV was confirmed by western blots and ELISA. The experimental inoculations represent the first documented report of BYMV in the annual L. succulentus and biennial L. texensis species. Since BYMV is seedborne and transmitted by many aphid species (3), it is possible that several lupine transplants escaped potyvirus detection, and secondary transmission of BYMV to plants occurred by aphids. During the 1950s, BYMV was confirmed in several annual lupines grown as crops in the southeastern United States (3). To our knowledge, this is the first report of BYMV occurring naturally in a lupine species in Washington. BYMV is a destructive virus to lupine species worldwide and has a wide host range in Fabaceae. This research directly contributes toward the maintenance of virus-free lupine seed for distribution to scientists focusing on lupine research.

Resistance of peas to Sclerotinia sclerotiorum in the Pisum core collection

In this study, 497 pea accessions from the Pisum core collection located at the USDA‐ARS, Western Regional Plant Introduction Station (WRPIS), Pullman, WA and seven woody‐stem pea lines from a private collection in the UK, were screened for resistance to Sclerotinia sclerotiorum, the cause of white mould. All of the Pisum genotypes screened were susceptible to infection, and 237 of the 504 genotypes were highly susceptible since these did not survive 2 weeks post‐inoculation. However, 22 pea accessions and one woody‐stem line were identified with quantitative partial resistance to white mould. Pea accessions 103709, 166084, 169603, 240515 and 270536 from the core collection demonstrated the greatest quantitative partial resistance to S. sclerotiorum based on nodal resistance and plant survival in replicated greenhouse and laboratory tests. Only five of the 504 genotypes screened had a mean lesion length of between 0 and 1 cm when assessed 3 days post‐inoculation. Pea stem diameter was significantly (P ≤ 0·03) negatively correlated with stem lesion length in replicated greenhouse and laboratory experiments, and was determined to be the best predictor of quantitative partial resistance to S. sclerotiorum based on lesion length.

Neotyphodium endophytes in tall fescue seed: viability after seed production and prolonged cold storage

This research quantified frequencies of Neotyphodium-infected (E+) tillers and mature seed from E+ plants of two wild tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire (= Festuca arundinacea Schreb.) accessions from the Mediterranean basin that were stored in the seed bank at the USDA, ARS Western Regional Plant Introduction (PI) Station, Pullman, Washington USA. Tiller-infection levels were high in glasshouse (>97%) and field (100%) plants of each accession and over 99% of the seed from E+ plants of both accessions harbored viable Neotyphodium endophyte. Seed germination was either slightly improved (Morocco accession) or not affected (Italy) by endophyte infection. High levels of viable E+ seed were produced by E+ field plants grown under a wide range of ambient temperatures (-27° to 37°C). These collective results suggest that viable endophyte is retained with current seed-regeneration practices at the Pullman PI Station. This study also documented viable Neotyphodium infection frequencies (16-100%) in plants grown from seed of 20 additional Mediterranean tall fescue accessions stored for four to ten years in the Pullman seed bank. For some of these accessions, low post-storage infection frequencies, in comparison with their high initial viability levels, suggested a decline in endophyte viability during seed storage. Additional evidence for diminishing endophyte viability levels in some accessions was provided by Polymerase Chain Reaction (PCR), immunoblot, and microscopic seed assays.

Carrot Seed Germination at High Temperature: Effect of Genotype and Association with Ethylene Production

Carrot (Daucus carota L.) seed germination may be erratic or reduced under high temperatures (above 35 °C). Even in tropical genotypes (tolerant to high temperatures during crop development), the negative effects of high temperatures on carrot stand establishment have been observed, especially during summer. The objectives of this study were to characterize commercial carrot cultivars and accession lines for their ability to germinate at high temperature and determine the ethylene production during imbibition at high temperature. Seeds from 34 commercial cultivars and 125 carrot accessions from the North Central Regional Plant Introduction Station were germinated at 25 °C (optimal) and 35 ± 0.5 °C (high) in constant light. Ethylene production during seed imbibition at high temperature was evaluated in some genotypes. Many of the commercial cultivars had reduced germination at 35 °C. ‘XPC-3617’, ‘Alvorada’, ‘Brasilia’, and ‘Esplanada’ had the greatest germination at 35 °C. A greater number of accessions germinated at 35 °C than did the commercial genotypes. The accession PI 319858 germinated 95% at both temperatures and was considered thermotolerant. Six accessions (Ames 7665, Ames 7698, Ames 25031, PI 167082, PI 294637, and PI 319858) germinated above 80% at 35 °C and were also identified as potential sources of thermotolerance. Fifteen other accessions (Ames 7694, Ames 25031, Ames 25036, Ames 25049, Ames 25705, PI 167082, PI 179687, PI 180834, PI 261782, PI 269486, PI 273658, PI 277710, PI 288242, PI 294637, and PI 319858) had thermotolerance ratios of T35/T25 0.85 or greater (where T35 = germination at 35 °C and T25 = germination at 25 °C) and were identified for further testing. The identified thermotolerant genotypes might be useful for carrot seed germination mechanism studies as well as for breeding programs. Ethylene production during seed germination at high temperature was greater in thermotolerant genotypes than in thermosensitive genotypes. High correlations were observed between first germination count at 35 °C and ethylene production, total germination at 35 °C and ethylene production, and thermotolerance ratio and ethylene production.