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Matthew D. Clark and Eric Watkins

Prairie junegrass [Koeleria macrantha (Ledeb.) Shultes] is a perennial, short-grass prairie species distributed throughout the Northern Hemisphere that is being evaluated for use as a low-input turf. In June 2007, 300 genotypes representing collection locations derived from Colorado, Nebraska, and Minnesota germplasm were grown and evaluated 3 years for turfgrass performance characteristics in a randomized complete block design with five clonal replications at two locations (St. Paul, MN, and Becker, MN). After establishment, plots received no supplemental irrigation or fertility and were mowed weekly to a height of 6.4 cm. Broad-sense heritability estimates were calculated on a clonal mean (Hc) and single-plant (Hsp) basis for turf quality (Hc = 0.62, Hsp = 0.13), crown density (Hc = 0.55, Hsp = 0.09), mowing quality (Hc = 0.59, Hsp = 0.09), and genetic color (Hc = 0.45, Hsp = 0.06). The heritability estimates indicate that selection for these traits should result in significant gains in germplasm improvement. Differences were observed in the means and variances among clones, collection locations, and/or collection regions for many of the traits evaluated including rust severity (Puccinia spp.), spring green-up, plant height, lateral spread, vertical regrowth, and flowering traits. The positive correlations among some of these traits and those with moderate heritability estimates should allow for multi-trait selection in cultivar development.

Open access

Laise S. Moreira and Matthew D. Clark

Seedlessness is one of the most desirable traits for table and raisin grapes. Stenospermocarpic cultivars are desirable because they have large berries with superior quality. Embryo rescue techniques have been widely used to get progeny seedling populations from crosses using seedless mother plants. Selection of the female parent, sampling time, and the growth medium are the most crucial to the success of this technique. This study investigated the effect of best sampling time and media composition on embryo rescue efficiency in a cold-hardy hybrid grape breeding program. We sampled ovules 5 to 9 weeks after flowering, and we tested four media compositions. The greatest percentages of embryo germination and normal seedlings were obtained when ovules were harvest at 8 weeks after flowering, indicating that it is suitable to harvest ovules at veraison, when the extraction of ovules is easier as a result of softer berry flesh. For the media composition experiment, all ovules were harvested at 8 weeks after flowering. Nitsch & Nitsch culture medium had very low germination, and the resulting seedlings performed the lowest compared with the other treatments. Lloyd & McCown Woody Plant Basal Medium (WPM) increased the number of embryos germinated significantly, and a number of normal seedlings and plantlets developed. Although there was no significant difference among the other three media containing WPM supplemented with different doses of plant regulators, the WPM Plus medium [with cytokinin (6-benzlaminopurine), indole-3-butyric acid, gibberellin, and casein hydrolysate] promoted the greatest percentage of established plants (46.98%). Therefore, the 8-weeks-after-flowering harvest time and the WPM Plus medium were selected for use in the embryo rescue protocol at the University of Minnesota grape breeding program.

Open access

Andrew Sherwood, Lisa W. Alexander, Matthew D. Clark, Steve McNamara, and Stan C. Hokanson

Oakleaf hydrangea (Hydrangea quercifolia Bartr.) is an understory shrub native to the southeastern United States. Hydrangeas are popular ornamental landscape plants; however, little is known about the diversity in horticulturally important traits for oakleaf hydrangea. Information regarding the variation in important traits could guide future breeding efforts for the species. Seed was collected from 55 populations throughout the range of the species for the purpose of conducting a horticultural characterization of the species compared with select cultivars. Plant architecture was characterized as plant height, number of nodes, internode length, number of branches, and plant width. Plant architecture was measured for container-grown and field-grown plants in two locations (Minnesota and Tennessee). Tolerance to leaf spot (Xanthomonas campestris L.) was characterized for wild-collected seedlings and cultivars by measuring disease severity under exposure to ambient inoculum. Cold hardiness was characterized during two winters with a controlled freezing experiment. During the first winter, seedlings were tested in January; during the second winter, seedlings and cultivars were tested monthly from October through April. Plant architecture varied by environment, with plants growing larger in Tennessee than in Minnesota. The heights of container-grown and field-grown plants were correlated with the collection site latitude (r = −0.66), with populations from the northeastern extent of the range of the species being the most compact, and populations from Florida being the tallest. Leaf spot severity varied significantly among populations and cultivars and was also correlated with latitude for the seedlings (r = 0.70). Two populations in Florida were identified as sources of high tolerance to leaf spot, whereas ‘Flemygea’ and ‘Alice’ were identified as having moderate tolerance to leaf spot. Cold hardiness varied among populations and cultivars and among months of the winter. The overall maximum cold hardiness was observed in February [mean lethal temperature (LT50) = −33.7 °C], and several populations maintained an extreme level of cold hardiness into late winter. Midwinter cold hardiness also varied by latitude (r = −0.65), with northern populations showing higher levels of cold hardiness. These results indicate that certain wild oakleaf hydrangea populations will be useful for introgressing novel variation into breeding programs.

Free access

Cari A. Schmitz, Matthew D. Clark, James J. Luby, James M. Bradeen, Yingzhu Guan, Katherine Evans, Benjamin Orcheski, Susan Brown, Sujeet Verma, and Cameron Peace

Establishing marker-locus-trait associations to enable marker-assisted breeding depends on having an extensive, reliable database for phenotypic traits of interest in relevant germplasm. A reference germplasm set of 467 apple (Malus ×domestica Borkh.) cultivars, selections, and seedlings (referred to as individuals) was identified as part of the USDA-Specialty Crop Research Initiative (SCRI) project, RosBREED. The germplasm set provides efficient allelic representation of current parents in RosBREED demonstration apple breeding programs at Cornell University, Washington State University, and the University of Minnesota. Phenotyping at the three locations was conducted according to standardized protocols, focusing on fruit traits evaluated at harvest and after 10 and 20 weeks of refrigerated storage. Phenotypic data were collected for the sensory texture traits of firmness, crispness, and juiciness as well as for instrumental texture measures. In 2010 and 2011, fruit from 216 and 330 individuals, respectively, were harvested and a total of 369 individuals were evaluated over the two years. Correlations between sensory and instrumental texture measures were high in some instances. Moderate year-to-year repeatability of trait values was observed. Because each location had a largely unique set of individuals, as well as differing environmental conditions, means, ranges, and phenotypic variances differed greatly among locations for some traits. Loss of firmness and crispness during storage was more readily detected instrumentally than by the sensory evaluation.

Open access

David C. Zlesak, Darcy Ballantyne, Matthew Holen, Andrea Clark, Stan C. Hokanson, Kristen Smith, Jason D. Zurn, Nahla V. Bassil, and James M. Bradeen

The fungal pathogen, Diplocarpon rosae, infects only roses (Rosa spp.) and leads to rose black spot disease. Rose black spot is the most problematic disease of outdoor-grown roses worldwide due to the potential for rapid leaf chlorosis and defoliation. Eleven races of the pathogen were previously characterized from isolates collected in North America and Europe. Isolates of D. rosae obtained from infected leaves of the roses Brite EyesTM (‘RADbrite’; isolate BEP; collected in West Grove, PA) and Oso Easy® Paprika (‘CHEwmaytime’; isolate PAP; collected in Minneapolis, MN) proved to have unique infection patterns using the established host differential with the addition of Lemon FizzTM (‘KORlem’). The new races are designated race 12 (BEP) and race 13 (PAP), respectively, and Lemon FizzTM should be included in the updated host differential because it distinguishes races 7 and 12. Additionally, inconsistent infections and limited sporulation were found in the host differential Knock Out® (‘RADrazz’) for races 7 and 12. Expanding the collection of D. rosae races supports ongoing research efforts, including host resistance gene discovery and breeding new rose cultivars with increased and potentially durable resistance.