North American Germplasm Research Articles

Genetic Diversity of New Almond Accessions from Central Asian and Cold-adapted North American Germplasm

We evaluated the genetic diversity of a newly available collection of 94 almond [Prunus dulcis (Mill.) D.A. Webb] accessions from the former Improving Perennial Plants for Food and Bioenergy (IPPFBE) Foundation. Most of the collection (87 accessions) were collected as seeds from trees growing in the central Asian nations of Kyrgyzstan, Tajikistan, and Uzbekistan, and included several examples of Prunus bucharica (Korsh.) Hand.-Mazz, and related wild species. Of the remaining accessions, six were sourced from a nursery in northern Utah in the United States, and one was a seedling of ‘Nonpareil’, a major commercial cultivar. DNA fingerprints were generated from 10 simple sequence repeat markers. To evaluate the comparative diversity of these new accessions, 66 accessions from the US Department of Agriculture, National Plant Germplasm System (NPGS) almond germplasm collection near Davis, CA, USA, were also included. These NPGS accessions were chosen to represent those collected in similar regions of Central Asia and the Caucasus. The fingerprints were analyzed via hierarchical clustering, principal components analysis (PCA), and discriminant analysis of principal components (DAPC). Hierarchical clustering suggested that half of the Utah-sourced accessions are closely related to each other and to the ‘Nonpareil’ seedling. Additional close relationships were detected (including at least one duplication or mislabeling), and two P. bucharica accessions from the IPPFBE collection were separated from the rest of the collection. A plot of the first two principal components clearly separated wild almond relatives (P. bucharica and Prunus fenzliana Fritsch) from the remaining accessions. PCA after removal of the wild species separated the ‘Nonpareil’ seedling, the Utah-sourced accessions, and many of the IPPFBE accessions (mostly from Uzbekistan) from nearly all other individuals. The third principal component identified an additional population structure that separated groups of predominantly IPPFBE or NPGS accessions. DAPC showed a considerable admixture of accessions from Azerbaijan, and a little to no admixture of accessions from Georgia and Tajikistan. These results suggest that central Asian/Caucasian almond germplasm is generally distinct from ‘Nonpareil’ and its relatives, and that although there is overlap between the NPGS and IPPFBE collections from this region, the IPPFBE collection does enhance the diversity of available almond germplasm.

Genetic variation and population structure in China summer maize germplasm

Maize (Zea mays L.) germplasm in China Summer maize ecological region (CSM) or central corn-belt of China is diverse but has not been systematically characterized at molecular level. In this study, genetic variation, genome diversity, linkage disequilibrium patterns, population structure, and characteristics of different heterotic groups were studied using 525,141 SNPs obtained by Genotyping-By-Sequencing (GBS) for 490 inbred lines collected from researchers at CSM region. The SNP density is lower near centromere, but higher near telomere region of maize chromosome, the degree of linkage disequilibrium (r2) vary at different chromosome regions. Majority of the inbred lines (66.05%) show pairwise relative kinship near zero, indicating a large genetic diversity in the CSM breeding germplasm. Using 4849 tagSNPs derived from 3618 haplotype blocks, the 490 inbred lines were delineated into 3 supergroups, 6 groups, and 10 subgroups using ADMIXTURE software. A procedure of assigning inbred lines into heterotic groups using genomic data and tag-SNPs was developed and validated. Genome differentiation among different subgroups measured by Fst, and the genetic diversity within each subgroup measured by GD are both large. The share of heterotic groups that have significant North American germplasm contribution: P, SS, IDT, and X, accounts about 54% of the CSM breeding germplasm collection and has increased significantly in the last two decades. Two predominant types of heterotic pattern in CSM region are: M-Reid group × TSPT group, and X subgroup × Local subgroups.

Susceptibility of SEO/‘Harlayne’ type resistant apricot cultivars to PPV-T

Plum pox virus (PPV) is one of the most detrimental diseases of the Prunus species. The use of genetic resistance is the most promising solution for the control of the virus. To date, in apricot the resistance has only been found in the North American germplasm. The American cultivars ‘Stark Early Orange’ (SEO), ‘Goldrich’, ‘Harlayne’, ‘Stella’, and ‘Harcot’ are known as resistant against to PPV-D and M strain, both of which are the most common strains in Europe. These cultivars host a major locus located on the Linkage Group One (LG1) accounting for 70% of PPV resistance. In a previous study, Turkish apricot germplasm was screened for three markers which are known to be linked to the resistance locus on LG1 and five accessions in the Turkish collection were identified to host the markers. Here we report the first two years results of the biological test applied to the same collection. Biological test was commenced in Kayseri in 2012 by graft inoculating the accession with a PPV-T (Turkey) strain. After examinations in two consecutive years, we observed that SEO, ‘Harlayne’, ‘Harcot’ and the five accessions of Turkish apricot germplasm with resistance markers fail to show resistance to PPV-T. However, in the third year of observation the symptom level decreased on the resistant accessions.

Genetic Architecture of Flooding Tolerance in the Dry Bean Middle-American Diversity Panel.

Flooding is a devastating abiotic stress that endangers crop production in the twenty-first century. Because of the severe susceptibility of common bean (Phaseolus vulgaris L.) to flooding, an understanding of the genetic architecture and physiological responses of this crop will set the stage for further improvement. However, challenging phenotyping methods hinder a large-scale genetic study of flooding tolerance in common bean and other economically important crops. A greenhouse phenotyping protocol was developed to evaluate the flooding conditions at early stages. The Middle-American diversity panel (n = 272) of common bean was developed to capture most of the diversity exits in North American germplasm. This panel was evaluated for seven traits under both flooded and non-flooded conditions at two early developmental stages. A subset of contrasting genotypes was further evaluated in the field to assess the relationship between greenhouse and field data under flooding condition. A genome-wide association study using ~150 K SNPs was performed to discover genomic regions associated with multiple physiological responses. The results indicate a significant strong correlation (r > 0.77) between greenhouse and field data, highlighting the reliability of greenhouse phenotyping method. Black and small red beans were the least affected by excess water at germination stage. At the seedling stage, pinto and great northern genotypes were the most tolerant. Root weight reduction due to flooding was greatest in pink and small red cultivars. Flooding reduced the chlorophyll content to the greatest extent in the navy bean cultivars compared with other market classes. Races of Durango/Jalisco and Mesoamerica were separated by both genotypic and phenotypic data indicating the potential effect of eco-geographical variations. Furthermore, several loci were identified that potentially represent the antagonistic pleiotropy. The GWAS analysis revealed peaks at Pv08/1.6 Mb and Pv02/41 Mb that are associated with root weight and germination rate, respectively. These regions are syntenic with two QTL reported in soybean (Glycine max L.) that contribute to flooding tolerance, suggesting a conserved evolutionary pathway involved in flooding tolerance for these related legumes.

Characterization of resistance to the wheat stem sawfly in spring wheat landrace accessions from targeted geographic regions of the world

Plant landraces have long been recognized as potential gene pools for biotic and abiotic stress-related genes. This research used spring wheat landrace accessions to identify new sources of resistance to the wheat stem sawfly (WSS) (Cephus cinctus Norton), an important insect pest of wheat in the northern Great Plains of North America. Screening efforts targeted 1409 accessions from six geographical areas of the world where other species of grain sawflies are endemic or where a high frequency of accessions possesses the resistance characteristic of solid stems. Resistance was observed in approximately 14% of accessions. Half of the lines displayed both antixenosis and antibiosis types of resistance. Among the resistant accessions, 41% had solid or semi-solid stems. Molecular genetic screening for haplotypes at the solid stem QTL, Qss.msub.3BL, showed that 15% of lines shared the haplotype derived from ‘S-615’, the original donor of the solid stem trait to North American germplasm. Other haplotypes associated with solid stems were also observed. Haplotype diversity was greater in the center of origin of wheat. Evaluation of a representative set of resistant landrace accessions in replicated field trials at four locations over a three year period identified accessions with potential genes for reduced WSS infestation, increased WSS mortality, and increased indirect defense via parasitoids. Exploitation of distinct types of plant defense will expand the genetic diversity for WSS resistance currently present in elite breeding lines.

Susceptibility of Hop Cultivars to Downy Mildew: Associations with Chemical Characteristics and Region of Origin

Hop downy mildew (caused by Pseudoperonospora humuli) is a yield-limiting disease in many hop-production regions of the world. In this research, 110 cultivars that are or were widely grown in the United States, Europe, or Australasia were evaluated in western Oregon over three years for their reaction to the shoot infection phase of downy mildew and vigor. There was a large range of downy mildew susceptibility and vigor amongst commercial cultivars, with some cultivars possessing a very high level of resistance. Overall, however, disease resistance and vigor were significantly greater in cultivars originating from Europe than those originating from the United States, Japan, and Australia/New Zealand. Amongst a subset of 79 cultivars, vigor was negatively correlated with levels, in cones, of cohumulone, a chemical constitute of bittering acids typically found in germplasm derived from North America. The generally poor vigor observed in cultivars derived outside of Europe likely is indicative of a lack of tolerance to the crown infection phase of the disease. Thus, the best sources of downy mildew resistance seems to be found in cultivars from the United Kingdom and continental Europe, and such cultivars are typically lower yielding and lack distinctive aroma and flavor characteristics presently desired by craft brewers. Introgression of downy mildew resistance into North American germplasm with high yield and desirable brewing characteristics is needed. Accepted for publication 3 March 2016. Published 7 March 2016.

Study on Essential Derivation in Maize: III. Selection and Evaluation of a Panel of Single Nucleotide Polymorphism Loci for Use in European and North American Germplasm

ABSTRACTPairwise distance data for maize (Zea mays L.) inbred lines generated using sets of single nucleotide polymorphisms (SNPs) selected from a 50k Infinium array were compared with pairwise distances generated using a set of 163 simple sequence repeat (SSR) loci previously identified to help determine essentially derived variety (EDV) status (UPOV, 1991). Final comparisons were made using 26,874 SNPs after discarding SNPs with insufficient data quality or vulnerability to ascertainment bias. Inbred lines developed in the United States or in western Europe that had been previously published to establish SSR‐based thresholds provided the means to determine equivalent SNP‐based protocols. Use of 3072 SNPs selected to provide even genomic coverage according to genetic and physical maps provided robust, precise, high discrimination among inbred lines with consistent zonal classification with up to 20% missing data. Comparisons of intercepts and slopes for SSR and SNP inbred pairwise distance data translated the 82% SSR green‐orange similarity threshold to 91% using SNPs and the 90% SSR orange‐red threshold to 95% using SNPs. Information required to conduct analyses using these 3072 SNPS is presented.

Genetic Variability for Biofuel Traits in a Circumglobal Reed Canarygrass Collection

ABSTRACTReed canarygrass (Phalaris arundinacea L.), a cool‐season perennial forage crop that grows well in cool, wet climates, has potential value as an energy crop. Nevertheless, little breeding effort has gone into its development as an energy crop. We evaluated 94 reed canarygrass accessions for agronomic and quality traits at Ames, IA, and Arlington, WI, in 1999 and 2000. Variation among accessions was observed for all variables. Biomass yield was not correlated with acid detergent fiber (cellulose plus lignin) or with acid detergent lignin, indicating good potential for developing favorable feedstocks for co‐firing or for fermentation. Analysis of regional geographic variation as well as principal component analysis showed that phenotypes varied considerably among geographic regions, with much of the variation attributable to differences between Europe and Asia. Except for North American germplasm, European germplasm tended to have higher biomass yield than other germplasm, suggesting that it may be better suited for use in direct breeding programs in the north central United States. Overall, sufficient variation exists among wild and cultivated germplasm to warrant further breeding of reed canarygrass as a biofuel feedstock.

Single nucleotide polymorphism discovery in elite north american potato germplasm

BackgroundCurrent breeding approaches in potato rely almost entirely on phenotypic evaluations; molecular markers, with the exception of a few linked to disease resistance traits, are not widely used. Large-scale sequence datasets generated primarily through Sanger Expressed Sequence Tag projects are available from a limited number of potato cultivars and access to next generation sequencing technologies permits rapid generation of sequence data for additional cultivars. When coupled with the advent of high throughput genotyping methods, an opportunity now exists for potato breeders to incorporate considerably more genotypic data into their decision-making.ResultsTo identify a large number of Single Nucleotide Polymorphisms (SNPs) in elite potato germplasm, we sequenced normalized cDNA prepared from three commercial potato cultivars: 'Atlantic', 'Premier Russet' and 'Snowden'. For each cultivar, we generated 2 Gb of sequence which was assembled into a representative transcriptome of ~28-29 Mb for each cultivar. Using the Maq SNP filter that filters read depth, density, and quality, 575,340 SNPs were identified within these three cultivars. In parallel, 2,358 SNPs were identified within existing Sanger sequences for three additional cultivars, 'Bintje', 'Kennebec', and 'Shepody'. Using a stringent set of filters in conjunction with the potato reference genome, we identified 69,011 high confidence SNPs from these six cultivars for use in genotyping with the Infinium platform. Ninety-six of these SNPs were used with a BeadXpress assay to assess allelic diversity in a germplasm panel of 248 lines; 82 of the SNPs proved sufficiently informative for subsequent analyses. Within diverse North American germplasm, the chip processing market class was most distinct, clearly separated from all other market classes. The round white and russet market classes both include fresh market and processing cultivars. Nevertheless, the russet and round white market classes are more distant from each other than processing are from fresh market types within these two groups.ConclusionsThe genotype data generated in this study, albeit limited in number, has revealed distinct relationships among the market classes of potato. The SNPs identified in this study will enable high-throughput genotyping of germplasm and populations, which in turn will enable more efficient marker-assisted breeding efforts in potato.

ADVANCES IN LOW-CHILLING PEACH BREEDING AT INSTITUTO AGRONÔMICO, SÃO PAULO STATE, BRAZIL

Peach (Prunus persica L. Batsch), a typically temperate fruit tree, was introduced in Brazil through Portuguese colonization in the 1530s. Peach trees established at low latitude regions require climatic adaptation to subtropical-temperate conditions of low-chilling. The first Brazilian peach breeding program was initiated by O. Rigitano in the late 1940s at the Instituto Agronomico (IAC). Research continued at IAC, aiming at full adaptation of selections to different climates of Sao Paulo State and other similar ecosystems. Pioneering peach crosses involved local and North American germplasm material of medium chilling requirement. Various low-chill and productive cultivars with high quality fruits were released. In the last decades, the best IAC cultivars (F 1 and F 2 hybrids) were intercrossed with peach and nectarine selections from the University of Florida. Fifty eight cultivars were released for areas with 0-200 chilling hours (below 7.2°C). The main fruit traits are: epidermis - green ('Talisma', 'Nectar', 'Cristal'), yellow ('Canario'), pink ('Joia-1 and 2'), red ('Centenario'); flesh - yellow ('Petisco-2', 'Dourado-1'), white ('Natal', 'Delicioso Precoce', 'Joia-4'); texture - firm, non-melting ('Aurora-1'), soft ('Tutu', 'Catita', 'Joia-3'); stone - cling ('Colibri', 'Brasao'), free ('Dourado-2', 'Joia-5'); flavor - sweet ('Supermel', 'Ouromel-2'), sweet-acid ('Petisco', 'Arlequim'), canning ('Regis', 'Biuti'); maturation - early ('Tropical-1 and 2'), medium ('Aurora-2', 'Docura-2'), late ('Bolao', 'Momo'); extra-large size ('Douradao'), and others, as shape - globose, oblong, round, with or without tip; pubescence - high, medium, low; dual purpose (fresh-canning). About 46% of 58 cultivars has yellow flesh, 54% white flesh, 47% rose and red skin, 53% green and yellow skin, 65% are freestone and 35% clingstone, being 10% canning. IAC peach harvest occurs from August to February, about 80-180 days after full bloom. These cultivars, and other genotypes with better pomological characteristics, have been widely accepted by fruit growers and consumers, due to the adequate evolution of peach cultivation in subtropical areas.

A model of the genetic differences in malting quality between European and North American barley cultivars based on a QTL study of the cross Triumph × Morex

With 2 figures and 2 tables AbstractTo study the genetic control of malting quality, in North American and European barley varieties, over five contrasting environments, 106 doubled haploid (DH) lines, from the cross ‘Triumph’ × ‘Morex’, were grown at Pullman (Washington State, USA) in 2002, Dundee (Scotland) in 2003 and 2005 and Lleida and Valladolid (Northern Spain) in 2006. The vrs locus, associated with two‐row vs. six‐row ear type, had a significant effect, as two‐row lines had higher grain protein content at all sites. This had variable effects on other malting parameters, but hot water extract (EXT) was not significantly affected at the two Spanish sites. Quantitative trait loci associated with malting characters were distributed across all seven chromosomes, but the most influential, with effects on EXT and alcohol yield, at more than one site, were on 1H, with ‘Morex’ providing the increasing allele and 5H, with the increasing allele from ‘Triumph’. Transgressive segregation, in both directions, occurred at all sites. It was concluded that crosses between European and North American germplasm could enhance quality attributes in barley cultivated across diverse environments.

A native QTL for Fusarium head blight resistance in North American barley (Hordeum vulgareL.) independent of height, maturity, and spike type loci

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein.) Petch), is one of the major diseases of barley (Hordeum vulgare L.) in eastern China, the Upper Midwest of the USA, and the eastern Prairie Provinces of Canada. To identify quantitative trait loci (QTL) controlling FHB resistance, a recombinant inbred line population (F6:7) was developed from the cross Zhenongda 7/PI 643302. The population was phenotyped for resistance to FHB in two experiments in China and four experiments in North Dakota. Accumulation of the mycotoxin deoxynivalenol was determined in one experiment in China and two in North Dakota. Simplified composite interval mapping was performed on the whole genome level using the software MQTL. The QTL FHB-2 from PI 643302 for FHB resistance was found on the distal portion of chromosome 2HL in all six FHB screening environments. This QTL accounted for 14% of phenotypic variation over six environments and was not associated with heading date or plant height. The FHB resistance QTL FHB-2 detected near the end of chromosome 2HL is in a different location from those found previously and is therefore probably unique. Because the QTL was not contributed by the Chinese cultivar Zhenongda 7, it is likely a native QTL present in North American barley. The QTL FHB-2 represents the first reported QTL for native FHB resistance in North American germ plasm and has been given the provisional name Qrgz-2H-14. This QTL should be considered for pyramiding with other FHB QTL previously mapped.

DNA Polymorphisms Reveal Geographic Races of Reed Canarygrass

ABSTRACTReed canarygrass (Phalaris arundinacea L.) is a cool‐season perennial with a circumglobal distribution in the northern hemisphere, native to Europe, Asia, and North America. Repeated introductions of European germplasm into North America have created confusion over the origins of reed canarygrass germplasm found in wetlands, pastures, and breeding programs. The objectives of this study were to identify sources of DNA marker variation among reed canarygrass cultivars from Europe and North America and between landraces and improved cultivars from North America. Analysis of 205 reed canarygrass plants from 15 cultivars based on 102 amplified fragment length polymorphic (AFLP) DNA markers revealed two groups of cultivars. One group consisted of three closely related but geographically diverse North American landraces that were completely separated from all other plants in only two dimensions of the AFLP incidence matrix. The complete discrimination of these plants from all European plants suggests their possible origin from native North American germplasm. These results were supported by chloroplast DNA sequence analysis, which additionally revealed separation of a potential Scandinavian cytoplasmic race from the continental European cytoplasmic race. This is the strongest evidence to date suggesting that native North American reed canarygrass germplasm has been preserved within cultivars of this species.

Compounds of essential oils as markers of hop resistance (Humulus lupulus) to powdery mildew (Podosphaera macularis)

Field assessments of resistance to powdery mildew of 103 hop cultivars, analyses of hop essential oil and correlation between the score for powdery mildew and the relative percentage of essential oil compounds were performed over three years. Seven susceptibility markers (peaks 29 (methyl-5-methyl-hexanoate), 30 (myrcene), 34 (iso-amyl-iso-butyrate), 38 (1-8-cineole), 56 (methyl-octanoate), 88 (methyl decanoate) and 122 (undetermined peak)) and seven resistance markers (peaks 112 (santalene), 114 (germacrene-D), 118 (alpha-selinene), 138 (cariophylene epoxide), 26, 135 and 158 (undetermined peaks)) were selected from peaks with a positive or negative correlation between powdery mildew scores and their presence in the essential oil of extremely susceptible or resistance cultivars. The number and value of resistance/susceptibility markers decreased with an increase in the level of cultivar susceptibility/resistance. Susceptible cultivars mainly appeared to contain North American germplasm, while more resistant cultivars belong to European hops. Analysis of the presence/absence of the selected markers showed that the absence of susceptibility markers, particularly 30, 34 and 38, can be of practical value in resistance hop breeding.

Mapping quantitative trait loci for preharvest sprouting resistance in white wheat

The premature germination of seeds before harvest, known as preharvest sprouting (PHS), is a serious problem in all wheat growing regions of the world. In order to determine genetic control of PHS resistance in white wheat from the relatively uncharacterized North American germplasm, a doubled haploid population consisting of 209 lines from a cross between the PHS resistant variety Cayuga and the PHS susceptible variety Caledonia was used for QTL mapping. A total of 16 environments were used to detect 15 different PHS QTL including a major QTL, QPhs.cnl-2B.1, that was significant in all environments tested and explained from 5 to 31% of the trait variation in a given environment. Three other QTL QPhs.cnl-2D.1, QPhs.cnl-3D.1, and QPhs.cnl-6D.1 were detected in six, four, and ten environments, respectively. The potentially related traits of heading date (HD), plant height (HT), seed dormancy (DOR), and rate of germination (ROG) were also recorded in a limited number of environments. HD was found to be significantly negatively correlated with PHS score in most environments, likely due to a major HD QTL, QHd.cnl-2B.1, found to be tightly linked to the PHS QTL QPhs.cnl-2B.1. Using greenhouse grown material no overlap was found between seed dormancy and the four most consistent PHS QTL, suggesting that greenhouse environments are not representative of field environments. This study provides valuable information for marker-assisted breeding for PHS resistance, future haplotyping studies, and research into seed dormancy.

QTL in mega-environments: I. Universal and specific seed yield QTL detected in a population derived from a cross of high-yielding adapted × high-yielding exotic soybean lines

Modern soybean [(Glycine max (L.) Merrill] breeding programs rely primarily on the use of elite x elite line crosses to develop high-yielding cultivars. Favorable alleles for traits of interest have been found in exotic germplasm but the successful introduction of such alleles has been hampered by the lack of adaptation of the exotic parent to local mega-environment and difficulties in identifying superior progeny from elite x exotic crosses. The objective of this study was to use a population derived from a cross between an adapted and an exotic elite line to understand the genetic causes underlying adaptation to two mega-environments (China and Canada). A cross between a high-yielding Canadian cultivar 'OAC Millennium' and an elite Chinese cultivar 'Heinong 38' was performed to develop a recombinant inbred line (RIL) population. The RIL population was evaluated in China and Canada in multiple environments from 2004 to 2006. Significant variation for seed yield was observed among the RILs in both the Chinese and Canadian environment. Individual RILs performed differently between the Chinese and Canadian environments suggesting differential adaptation to intercontinental mega-environments. Seven seed yield quantitative trait loci (QTL) were identified of which five were mega-environment universal QTL (linked to markers Satt100, Satt162, Satt277, Sat_126, and the interval of Satt139-Sat_042) and two were mega-environment-specific QTL (at marker intervals, Satt194-SOYGPA and Satt259-Satt576). Seed yield QTL located near Satt277 has been confirmed and new QTL have been identified explaining between 9 and 37% of the phenotypic variation in seed yield. The QTL located near Satt100 explained the greatest amount of variation ranging from 18 to 37% per environment. Broad sense heritability ranged from 89 to 64% among environments. Epistatic effects have been identified in both mega-environments with pairs of markers explaining between 9 and 14% of the phenotypic variation in seed yield. An improved understanding of the type of QTL action as either universal or mega-environment-specific QTL as well as their interaction may facilitate the development of strategies to introgress specific high-yielding alleles from Chinese to North American germplasm and vice versa to sustain efforts in breeding of high-yielding soybean cultivars.

Compounds of essential oils as markers of hop resistance (Humulus lupulus) to powdery mildew (Podosphaera macularis)

Field assessments of resistance to powdery mildew of 103 hop cultivars, analyses of hop essential oil and correlation between the score for powdery mildew and the relative percentage of essential oil compounds were performed over three years. Seven susceptibility markers (peaks 29 (methyl-5-methyl-hexanoate), 30 (myrcene), 34 (iso-amyl-iso-butyrate), 38 (1-8-cineole), 56 (methyl-octanoate), 88 (methyl decanoate) and 122 (undetermined peak)) and seven resistance markers (peaks 112 (santalene), 114 (germacrene-D), 118 (alpha-selinene), 138 (cariophylene epoxide), 26, 135 and 158 (undetermined peaks)) were selected from peaks with a positive or negative correlation between powdery mildew scores and their presence in the essential oil of extremely susceptible or resistance cultivars. The number and value of resistance/susceptibility markers decreased with an increase in the level of cultivar susceptibility/resistance. Susceptible cultivars mainly appeared to contain North American germplasm, while more resistant cultivars belong to European hops. Analysis of the presence/absence of the selected markers showed that the absence of susceptibility markers, particularly 30, 34 and 38, can be of practical value in resistance hop breeding.

Genetic analysis infers Dt loci underlie resistance to Fusarium solani f. sp. glycines in indeterminate soybeans

Improved resistant cultivars are being developed to better withstand the sudden death syndrome (SDS) of soybean (Glycine max L. Merr.) caused by Fusarium solani (Mart.) Sacc. f. sp. glycines (Fsg) (renamed F. virguliforme). Field trials to identify and select SDS-resistant cultivars take several years and are expensive. Selection of seedlings in the greenhouse and marker assisted selection are faster and cheaper. Selection for loci contributing SDS is well established for southern US germplasm sources (Forrest, Pyramid) but untested in northern germplasm. The aim was to find DNA markers associated with loci contributing seedling resistance to F. solani in the northern germplasm cultivars Minsoy and Noir. The greenhouse assay used plants grown for 3 wk in F.solani inoculated soil. Disease severity (DS) was recorded for 2000 recombinant inbred lines (RIL) from Minsoy × Noir1 (M×N) after F. solani infestation and compared to the DS of non-infested controls. Minsoy was partially resistant and Noir1 was relatively susceptible to F. solani. The heritability of DS was 48%. Comparison of alleles at 247 loci with the DS trait identified three regions associated with DS. Two regions within a 16 cM region of linkage group L (U14) were identified by markers SAT99 (P = 0.0006, R2 = 7%) and SATT6 (P = 0.0013, R2 = 5%). One region on linkage group C1 (U10b_ was identified by A063_1 (P = 0.0011, R2 = 5%). Interacting loci explained an additional 12% (A280 and SAT99) and 10% (R28 and SATT6) of the variability in DS, mainly by increasing resistance in susceptible class at each quantitative trait loci (QTL). These loci jointly explain the major portion (34%) of heritable resistance to F.solani. The QTL did not correspond with the known loci that condition resistance in the field in southern US germplasm. The QTL were in regions of the genome that were previously determined to alter determinacy, plant morphology, leaf shape, stem thickness, plant height, maturity and water use. Here Minsoy was taller, had thicker stems, produced more root mass and more shoot mass than Noir 1 during Fsg infestati on. Height (r = 0.15, P = 0.03), root weight (r = 0.3, P = 0.0002) and shoot weight r = 0.4, P = 0.0001) were significantly negatively correlated with resistance to SDS. Therefore, we conclude the SDS resistance is a pleiotropic effect of shoot and root characters in Minsoy and Noir that may confound selection for resistance to SDS in North American germplasm. Key words: Determinacy, genetic map, soil borne disease, Fusarium solani f. sp. glycines, soybean, Fusarium virguliforme

Genetic progress from 40 years of orchardgrass breeding in North America measured under management-intensive rotational grazing

There has been considerable activity in breeding orchardgrass (Dactylis glomerata L.) cultivars in North America during the latter half of the 20th century. The objective of this study was to determine if genetic improvements in the North American orchardgrass germplasm pool have been realized or can be detected under management intensive grazing. Forty-three orchardgrass cultivars, in three maturity groups, representing adapted North American germplasm and potentially unadapted European germplasm, were evaluated under management-intensive rotational grazing at two locations in the northern USA. Cultivar means varied for apparent preference and this variation was largely due to herbage availability at State College, PA, where grazing pressure was relatively high, but to other factors at Arlington, WI, where grazing pressure was relatively low. North American cultivars tended to have higher net herbage accumulation than European cultivars, corresponding well to differences in forage yield of hay plots. Orchardgrass cultivars that were significantly higher in hay yield than their predecessors showed mixed results with respect to net herbage accumulation under grazing: some increases, some decreases, and some with no change. These results indicate that an individual orchardgrass cultivar can be well adapted to both management systems, only one of the two systems, or neither system. Genetic increases in net herbage accumulation may occur serendipitously, but directed selection for specific traits that confer productivity under grazing, or net herbage accumulation per se, will probably ensure a higher probability of success for an orchardgrass breeding program directed to pastures. Key words: Dactylis glomerata, cultivar evaluation, breeding, selection, grazing

Isozyme Variation within and among Accessions of Annual Phalaris Species in North American Germplasm Collections

Accessions of annual Phalaris species in germplasm collections lack adequate genetic characterization for utilization. The objective of this study was to assess the level of isozyme variability of five annual Phalaris species, including 49 annual canarygrass (P. canariensis L.; 2n = 2x = 12), 24 P. brachystachys Link. (2n = 2x = 12), 48 P. minor Retz. (2n = 4x = 28), 19 P. paradoxa L. (2n = 2x = 14), and P. angusta Nees ex Tris (2n = 2x = 14) accessions from North American germplasm collections. Eight enzymes were used to detect polymorphism within and among accessions by scoring the presence or absence of 62 bands. Polymorphism was detected in 6 of 19 bands in P. canariensis, 12 of 22 bands in P. brachystachys, 34 of 40 bands in P. minor, 19 of 29 bands in P. paradoxa, and 6 of 21 bands in P. angusta. Polymorphism was detected in 23 accessions (47%) P. canariensis, 15 accessions (63%) of P. brachystachys, 35 accessions (73%) of P. minor, four accessions (19%) of P. paradoxa and three accessions of P. angusta (100%). Within‐accession polymorphic indices ranged from 0 to 0.03 in P. canariensis, 0 to 0.02 in P. brachystachys, 0 to 0.06 in P. minor, 0 to 0.04 in P. paradoxa, and 0.01 to 0.04 in P. angusta. Jaccard's similarity coefficients ranged from 0.83 to 1.0 in P. canariensis, 0.78 to 1.0 in P. brachystachys, 0.47 to 1.0 in P. minor, 0.44 to 1.0 in P. paradoxa, and 0.81 to 0.86 in P. angusta. Little isozyme variation existed either within or among accessions of the four diploid species. Phalaris minor, an autotetraploid, possessed greater variation among accessions rather than within accessions. In summary, limited variation was detected by means of isozymes in these five annual Phalaris species obtained from North American germplasm collections.