Stan C. Hokanson

• Professor at University of Minnesota

Rosa setigera is the only dioecious rose species and displays cryptic dioecy. There is increased interest to use R. setigera in breeding programs due to its resistance to rose rosette disease. Expanded understanding of the reproductive biology of R. setigera can help breeders more efficiently introgress disease resistance and other desirable traits...

Tree conservation efforts have increasingly focused on intraspecific genetic diversity to help identify trees and populations for conservation. Disjunct populations and populations on the periphery of a species’ range may be useful genetic resources. Eastern hemlock (Tsuga canadensis (L.) Carrière), a common native conifer in the eastern United Sta...

Better identification of adaptive genetic variation across populations of woody species would accelerate breeding efforts by identifying germplasm with a greater likelihood of tolerance to abiotic stresses, minimizing the need for lengthy, initial screenings. For these studies to yield meaningful conclusions, the accurate selection of wild germplas...

Roses are among the most popular flowering landscape shrubs in the world. Rose black spot disease, caused by the pathogen Diplocarpon rosae Wolf, is the most serious disease of outdoor-grown roses worldwide. Both race-specific and horizontal resistances to rose black spot have been documented in Rosa spp. and both resistance forms are valuable to p...

Cryptodiaporthe corni is the causal agent of a destructive disease called golden canker, which affects Cornus alternifolia, known as the pagoda or alternate-leaved dogwood. Due to the association between Cr. corni and pagoda dogwood, we sought to determine whether this fungus was capable of living as an endophyte in pagoda dogwood and causing this...

The genus Rhododendron (Ericaceae), comprising over 1,000 species, has long been valued for its showy ornamental characteristics. Unfortunately, most cultivars lack any tolerance to neutral or high pH soils common in many parts of North America. Genetic variation for pH tolerance among cultivars or wild populations could improve the adaptability of...

Farges filbert (Corylus fargesii (Franch.) C.K. Schneid.) is a large tree (to 130’(39.6 m)) that is native to China where it occurs in mountain valleys in the east/central part of the country. Described by western botanists in the late 19th century, the tree was little known in the west until it was collected under the auspices of the North America...

Cold temperature is a major environmental factor limiting the diversity of woody plants grown in northern landscapes. Consequently, cold hardiness has been the primary selection criterion throughout the 57 year history of the University of Minnesota's Woody Landscape Plant Breeding Program. Specifically, the program focuses on developing woody land...

To reach the goal set by the United States Department of Energy to replace 30% of 2004 gasoline usage with biofuels by 2030, the U.S. will need to consider diverse biomass feedstock sources, such as the plant genus Alnus. This genus contains nitrogen-fixing species that grow in a wide variety of challenging conditions. This study focused on 13 spec...

Golden Canker is a common disease that frequently attacks pagoda dogwood (Cornus alternifolia L.) causing branch dieback, diffuse cankers, and occasionally stem mortality. The causal agent, Cryptodiaporthe corni (Wehm.) Petrak, is commonly found throughout much of the northcentral and eastern United States. An evaluation of 40 asymptomatic stems of...

Use of broad-leaved, evergreen rhododendrons (Rhododendron subg. Hymenanthes) in northern landscapes is primarily limited by their cold hardiness. The University of Helsinki introduced several cultivars derived from R. brachycarpum ssp. tigerstedtii with flower buds cold-hardy to -39°C. When these cultivars are grown at latitudes south of Helsinki,...

The Woody Landscape Plant Breeding project at the University of Minnesota has been in existence since 1954. The project was initiated largely to develop an extended palette of cold-hardy woody landscape plants for northern landscapes. Since its inception, it has been responsible for the release of 49 woody plant cultivars including large stature sh...

Black spot of rose is distributed throughout the world and is the most serious disease of roses (Rosa spp.) in the outdoor landscape. Resistance breeding has been frustrated by the occurrence of races of the causal pathogen Diplocarpon rosae. Races from Germany, North America and the UK have been characterized and maintained in a pathogenic state....

Introduction Germplasm Acquisition Central Asian Collections Maintenance Distribution Characterization and Evalution Utilization Conclusion Literature Cited

Development of the Modern Strawberry Genetic Fingerprinting and Gene Tagging Mapping In Vitro Biology, Genetic Transformation, and Gene Cloning Future Prospects Literature Cited

Forty-one deciduous azalea (Rhododendron subgen. Pentanthera G. Don) cultivars were assessed for powdery mildew (PM) resistance in a two-location, 3-year field trial. Disease severity (percent leaf area affected) on abaxial leaf surfaces was used to rate the level of field resistance. This measure was proportional to (r = 0.83) but higher than esti...

Cross-species transferability of simple sequence repeats (SSRs) is common and allows SSRs isolated from one species to be applied to closely related species, increasing the use of previously isolated SSRs. The genus Cornus consists of 58 species that are ecologically and economically important. SSRs have previously been isolated from C. florida and...

Black spot disease, incited by the fungus Diplocarpon rosae Wolf, is the most important disease of roses (Rosa hybrida L.) in the outdoor landscape. Though partial resistance exists in cultivated germplasm, the genetic basis of this trait has not yet been elucidated. Six diploid and six tetraploid rose cultivars were crossed in two factorial combin...

Black spot disease of rose, incited by the fungus Diplocarpon rosae, is found worldwide and is the most important disease of garden roses. A gene-for-gene interaction in this pathosystem is evidenced by the presence of pathogenic races of D. rosae and the previous discovery of a dominant resistance allele at the Rdr1 locus in the diploid Rosa multi...

Anthracnose crown rot of cultivated strawberry (Fragaria xananassa Duchesne ex Rozier) has been a major disease problem in the strawberry producing regions of the southeastern United States since the early 1970s. Chemical controls are often inadequate, but use of resistant cultivars is seen as a credible option for managing this disease. Only a sma...

The ability to store rose pollen allows for greater flexibility when crossing asynchronously flowering parents. However, storage conditions and duration may lead to gametophytic selection and affect the resulting sporophytic populations. The objective of this study was to compare degradation of rose pollen stored for relatively short (two weeks) an...

Blackspot disease of roses is the most destructive of rose diseases worldwide. Breeding for resistance to blackspot is made difficult by multiple races of the causal fungus, Diplocarpon rosae. In orDer to efficiently and accurately screen roses for resistance, a protocol must be developed or isolating, culturing, and maintaining races in a virulent...

A shrub rose hybridization program with the objective of developing USDA Zone 4 hardy, black spot tolerant, attractive, repeat blooming cultivars was initiated in 1990. Parental germplasm was selected from several taxa, including species roses, Old Garden roses, Shrub roses, Miniature roses, and Polyantha roses. Species roses and hardy cultivars am...

Black spot, incited by the fungus Diplocarpon rosae Wolf, is the most significant disease problem of landscape roses (Rosa hybrida L.) worldwide. The documented presence of pathogenic races necessitates that rose breeders screen germplasm with isolates that represent the range of D. rosae diversity for their target region. The objectives of this st...

Blackspot disease, caused by the fungus Diplocarpon rosae Wolf, is the most serious disease problem of roses worldwide. From a breeding perspective, the documented occurrence of races in the pathosystem necessitates the characterization of the race structure for the pathogen, identification of resistance genes in rose germplasm, and determination o...

Tissue-cultured 'Chandler' strawberry plants were grown in a greenhouse to produce stolons. Plantlet size and position on the stolon affected rooting and quality of transplants. Cold stored plantlets developed fewer roots than plantlets plugged fresh in July or August. In the field, fewer of transplants that were cold stored survived, but those tha...

In the perennial strawberry production system, removal of the harvested crop represents a loss of nitrogen (N) that may be influenced by cultivar. Eight strawberry (Fragaria xananassa Duch.) cultivars and eight numbered selections grown in advanced matted row culture were compared over three seasons for removal of N in the harvested crop. Replicate...

Although simple sequence repeat (SSR) markers have been developed for species in the closely related genera Fragaria L. (strawberry) and Rubus L. (raspberry and blackberry), the number of SSRs available is insufficient for genetic mapping. Our objective was to use and compare multiple approaches for developing additional SSRs for Fragaria and Rubus...

Additional index words. Fragaria ×ananassa, fruit breeding, Phytophthora fragariae, Colletotrichum, red stele, anthracnose 'Ovation', a June-bearing strawberry (Fragaria ×ananassa Duch. ex Rozier) cultivar, was introduced for propagation to nurseries quality fruits make 'Ovation' a good season extender even in locations and production systems where...

Strawberry ('Chandler') plants were grown in a greenhouse hydroponic culture system from 28 Apr. to 20 July to produce runners (stolons) with several daughter plants. By mid-July, each 'Chandler' plant had developed about 30 daughter plants on 12 runners with 1 to 6 daughter plants on each runner. Daughter plants varied in weight from <0.9 to >10 g...

Tissue-culture derived mother plants were established in a greenhouse suspended-gutter, nutrient-film technique growing system to evaluate runner tip productivity in the system. Effects of cultivar ('Allstar', 'Chandler', 'Latestar', 'Northeaster', and USDA selection B 27) and duration (0, 1, or 2 months) of cold storage at 1 degrees C on tip viabi...

Forty deciduous azalea ( Rhododendron sp. ) cultivars from commercial sources were evaluated for powdery mildew ( Microsphaera sp. ) resistance. Plants were established in two duplicate field plantings in Ohio and Minnesota and evaluated in 2002 and 2003. Plants were scored using a disease symptom rating based on the percent of leaf area infected,...

The etiology of pallidosis, a disease of strawberry identified more than 45 years ago, remains unknown. We report a putative agent of the disease, a virus belonging to the Crinivirus genus of the Closterovirideae family. A sensitive reverse transcription-polymerase chain reaction (RT-PCR) test has been developed. Polyclonal antibodies that can be u...

Soilless greenhouse culture systems were used for winter fruit production and to produce stolon tips for plug plant propagation in the summer. In the first study, 'frigo' transplants were potted in July and August. Rooted plants were transferred to a hydroponic system in early October. Harvest commenced in late October in dayneutral 'Aromas', 'DIAM...

Bacterial angular leafspot disease (Xanthomonas fragariae Kennedy and King) of strawberry (Fragaria species and F. xananassa Duch. cultivars) has become increasingly important to strawberry fruit and plant production. Strawberry cultivars and species vary in susceptibility to infection. However, little is known regarding epidemiology of the disease...

Anticipating the phaseout of methyl bromide, the USDA-ARS small fruit breeding program at Beltsville, Md., discontinued soil fumigation in strawberry breeding and selection trials in the mid 1990s. To address resulting weed and pathogen pests, a modified or advanced matted row system was developed. This system uses matted row-type culture, establis...

Bacterial angular leafspot disease (BALD) of cultivated strawberry, caused by the bacterium Xanthomonas fragariae, has become an increasingly serious disease problem. It is of particular concern because it is readily transmitted through asymptomatic nursery plants. Until now, there have been no sources of resistance to this pathogen identified in e...

An elite group of 38 strawberry accessions representing all subspecies of the beach strawberry [Fragaria chiloensis (L.) Miller] and the scarlet strawberry (F. virginiana Miller) was planted in a replicated design at five locations across the United States, and evaluated for plant vigor, flowering date, runner density, fruit set, fruit appearance,...

A collection of 142 accessions of 23 Malus species, derived hybrids and cultivar accessions from the USDA-ARS Plant Genetic Resources Unit's core collection, which represents an extensive range of Malus species, was screened with a set of previously described SSR (simple sequence repeat) markers. The markers were used to determine genetic identitie...

Nineteen of the major strawberry (Fragaria ananassa Duch.) cultivars grown in the UnitedStates and Canada were examined for AFLP markerpolymorphisms. For the AFLP reactions, the EcoRI-ACC primer was used in combination with fourMseI primers (MseI-CAC, MseI-CAG,MseI-CAT, or MseI-CTT). Each set ofprimers produced 46–66 scorable fragments ranging insi...

Commercial strawberry plantings in the mid-Atlantic region are often quickly infected with one or more aphid-transmitted viruses, resulting in the loss of plant vigor, stunting, lowered yields, etc. To produce virus-free plant material for the strawberry industry and for cultivar development programs, heat therapy and/or meristem tip culture protoc...

In a 1998 virus survey (2) conducted on 23 commercial strawberry (Fragaria × ananassa Duchesne) production farms in the state of Maryland, leaf samples from 1,100 randomly sampled plants were sent to the U.S. Department of Agriculture laboratory in Corvallis, OR, for testing by enzyme-linked immunosorbant assays (ELISA). The viruses identified were...

Strawberry (Fragaria x ananassa Duch.) cultivars used by commercial producers in North America often change rapidly due to several factors including modified cultural practices, processing and marketing practices, the desire for new cultivars with larger and higher quality berries, resistant insect and disease pests, loss of traditional chemical co...

Bacterial angular leafspot disease (BALD) of strawberry, caused by Xanthomonas fragariae Kennedy & King, has dramatically affected commercial fruit and plant production throughout the world. Leaf lesions may kill leaves, while lesions on sepals make fruit unmarketable. The bacterium can kill stolon-tip plantlets that are being rooted for transplant...

Malus sieversii, the main progenitor of the cultivated apple exhibits its maximum diversity in mountainous areas in southeast Kazakhstan. To represent this species better in the USDA-ARS germplasm collection, maintained in Geneva, NY, a co-operative project was initiated with the Republic of Kazakhstan to assess and collect that country's wild popu...

Larvae of several insects injure and kill strawberry (Fragaria xananassa Duchesne) plants by burrowing into and hollowing out plant crowns. Occasionally, these infestations are serious enough to cause heavy economic losses to fruit producers and nursery plant growers. In 1997 in Beltsville, Md., we observed wilting and dying mature plants and unroo...

 A collection of 66 Malus×domestica Borkh. accessions from the USDA-ARS Plant Genetic Resources Unit’s core collection was screened with a set of eight SSR (simple sequence repeat) primers developed at the PGRU in order to determine genetic identities, estimate genetic diversity, and to identify genetic relationships among these accessions. All eig...

Despite the commercial approval of twenty-five transgenic crops in the U.S. as of mid-1996, concern is still being expressed regarding the potential risks associated with genetically engineered crops. One recurring issue is the possibility of pollen-mediated escape of engineered genes into populations of crop wild relatives. To address this concern...

One of the concerns associated with the field testing and agronomic-scale release of transgenic crops is the potential for the pollen-mediated escape of engineered genes into naturally occurring populations of wild relatives. While border rows have been used frequently to restrict the pollen-mediated escape of engineered genes from field trials, th...

One of the primary progenitors of the cultivated apple is Malus sieversii L., a species native to the forested regions of central Asia. Despite the horticultural importance of M. sieversii, little is known about genetic variation in this species. In this study, allozyme diversity at 18 loci was determined for 259 seedlings belonging to 31 sib famil...

A further characterization of the cucumber ( Cucumis sativus L.) mutant `Wisconsin SMR-18' bla (blunt leaf apex) revealed a new character associated with the previously described leaf phenotype. The attachment of the blade to the petiole of bla plants is flat across, as opposed to the cordate or indented attachment in the wild-type `Wisconsin SMR-1...

The Apostle Islands in Lake Superior are populated by trees that are clearly related to Quercus rubra L. However, several islands have trees with morphological characteristics suggestive of hybridization with Q. ellipsoidalis Hill. Leaf specimens were collected from trees in five locations: the outermost island, an intermediate island, the nearest-...

Isozyme variability was examined in populations representing the red oak complex (Quercus subg. Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A concomitant study of morphometric variation described in the companion manuscript, revealed a continuum in leaf morphology extending from an in...

Additional index words. Abstract. Fragaria × ananassa, CO 2 assimilation, partitioning patterns Twenty-one western and 13 eastern strawberry [Fragaria × ananassa (Duch.)] cultivars were grown in a polyethylene-covered greenhouse (polyhouse) in deep beds at either 10 × 10 or 25 × 25 cm spacing. Runners were removed weekly from the closest-spaced pla...

Rose is one of the most economically important ornamental crops worldwide. Rosa sp. is well suited genus to become a model for woody ornamentals for a number of reasons: (i) its relative small genome size (500 Mb), (ii) its well documented genetic history with ploïdy events, (iii) its short life for a woody plant, and (iv) availability of different...

Thesis (M.S.)--Michigan State University. Dept. of Horticulture, 1991. Includes bibliographical references (leaves 39-43). Microfilm.