Search Results

You are looking at 121 - 130 of 145 items for

  • Author or Editor: John Clark x
Clear All Modify Search

Spinach (Spinacia oleracea L.) is an important vegetable worldwide with high nutritional and health-promoting compounds. Bolting is an important trait to consider to grow spinach in different seasons and regions. Plant height and leaf erectness are important traits for machine harvesting. Breeding slow bolting, taller, and more erect spinach cultivars is needed for improved spinach production. A total of 288 United States Department of Agriculture (USDA) spinach accessions were used as the association panel in this research. Single-nucleotide polymorphisms (SNPs) discovered through genotyping by sequencing (GBS) were used for genotyping. Two structured populations and the admixtures were inferred for the 288 spinach accession panel using STRUCTURE and MEGA. Association mapping was conducted using single-marker regression (SMR) in QGene, and general linear model (GLM) and mixed linear model (MLM) built in TASSEL. Three SNP markers, AYZV02001321_398, AYZV02041012_1060, and AYZV02118171_95 were identified to be associated with bolting. Eight SNP markers, AYZV02014270_540, AYZV02250508_2162, AYZV02091523_19842, AYZV02141794_376, AYZV02077023_64, AYZV02210662_2532, AYZV02153224_2197, and AYZV02003975_248 were found to be associated with plant height. Four SNP markers, AYZV02188832_229, AYZV02219088_79, AYZV02030116_256, and AYZV02129827_197 were associated with erectness. These SNP markers may provide breeders with a tool in spinach molecular breeding to select spinach bolting, plant height, and erectness through marker-assisted selection (MAS).

Free access

Muscadine (Vitis rotundifolia Michx.) vines may be male (M), female (F), or hermaphroditic (H). Male flowers have only filaments and anthers, whereas female and hermaphroditic flowers are morphologically perfect. Female flowers are distinguished from hermaphroditic flowers by their reflexed stamens (as opposed to upright) and nonfunctional pollen. Primers derived from previously identified candidate genes located at the sex locus of Vitis vinifera L. were used to generate amplicons from M, F, and H muscadine cultivars. Sequence analysis of the amplicons revealed insertion/deletion (indel) polymorphisms in a trehalose-6-phosphate phosphatase (TPP) gene (VR006) and a WRKY transcription factor 21 gene (VR009). Primers were designed to create diagnostic markers for each indel polymorphism. Associations between the marker alleles and the plant sex trait were examined in a wide range of muscadine germplasm and in segregating populations derived from F × H, F × M, and H × H crosses. VR006 produced a codominant marker that was able to differentiate the female-associated allele from the male- and hermaphroditic-associated alleles. The marker was able to detect female plants and will be suitable for screening breeding program progenies. VR009 was able to detect the presence of the female allele in most germplasm, but a crossover event appears to have separated the marker from the sex locus in some germplasm. As shown in previous muscadine genetic studies, H × H-derived populations produced male seedlings. Marker analysis of these populations indicates that male flowers only occur in seedlings which are heterozygous for F- and H-associated marker alleles and inheritance of flower type in muscadine remains unclear.

Free access

Fresh-market blackberries (Rubus subgenus Rubus Watson) have a growing global market, with continued release of cultivars to meet demand for consumer-quality fruit. The release of primocane-fruiting blackberry plants that produce crops on both floricanes and primocanes has expanded blackberry production. This study investigated the physiochemical attributes of fresh-market blackberries harvested from two cane types (floricane and primocane) from four primocane genotypes (APF-238, APF-268, ‘Prime-Ark® 45’, and ‘Prime-Ark® Traveler’) grown at the University of Arkansas Fruit Research Station, Clarksville in 2015 and 2016. Year-to-year differences were evident as blackberries harvested in 2016 were smaller (6 g) and less acidic (0.7% titratable acidity) than berries harvested in 2015 (8 g berries with 0.9% titratable acidity); however, soluble solids in each year were similar (≈10.2%). Differences in genotypes were also a factor. ‘Prime-Ark® Traveler’ (2015) and APF-268 (2016) had the highest berry firmness (7.8–8.3 N). In both years, APF-238 had the lowest firmness (5.7–6.0 N), highest isocitric acid (0.8–1.1 g/100 g), and highest total anthocyanins (239–353 mg/100 g). Floricane fruit harvested from ‘Prime-Ark® Traveler’ had the highest berry weights (8.3–10.4 g) in both years. Blackberries harvested from primocanes were wider (21.3–22.9 mm), had higher soluble solids (11.6% to 12.6%), and had lower titratable acidity (0.6%) when compared with floricane fruit in both years. Major year-to-year differences were found for several variables in this study, indicating that environmental effects can be substantial and growers should be aware of this influence on berries harvested from the different cane types. Evaluation of quality properties of floricane and primocane fruit of primocane plants in other locations would be valuable, particularly from areas where commercial blackberry production is established.

Free access

Primocane-fruiting blackberries (Rubus subgenus Rubus Watson) may offer opportunities for season extension and off-season fruit production, particularly in mild climates with protected culture. In May 2005, plants of ‘Prime-Jan’® were established at the Oregon State University–North Willamette Research and Extension Center, Aurora, OR. Half of the planting was established under a high tunnel and the remainder planted in an adjacent open field. In 2006 to 2007, primocanes were subjected to four treatments to promote branching and/or delay harvest: 1) all primocanes within the plot were cut to the ground when averaging 0.25 m tall, then later emerging canes soft-tipped when reaching 0.5 m tall (C0.25m/T0.5m); 2) all primocanes within the plot were cut to the ground when averaging 0.5 m tall, then later emerging canes soft-tipped when reaching 0.5 m (C0.5m/T0.5m); 3) primocanes double-tipped: all primocanes within the plot were soft-tipped when averaging 0.5 m tall with subsequent lateral branches then soft-tipped when reaching 0.5 m long (T0.5m/Tb0.5m); and 4) primocanes were soft-tipped when averaging 0.5 m tall (T0.5m; control). The tunnel was covered with plastic from 5 Sept. 2006 and 31 Aug. 2007, ≈1 to 2 weeks before harvest until the end of harvest to protect fruit from inclement weather. On average, fruit harvest began on 12 Sept. in the open field and tunnel, but lasted ≈3 weeks longer in the tunnel, ending on 16 Nov., on average. Primocanes that were double-tipped had nearly twice the flowers and fruit than canes that were soft-tipped only once (T0.5m; control). In the tunnel, cumulative yield of double-tipped primocanes averaged 10.7 t·ha−1 in 2006 and 19.3 t·ha−1 in 2007, a 267% and 159% increase compared with the control, respectively. On average, cumulative yield for all treatments was less in the open field than in the tunnel, although cultural systems could not be compared statistically. Harvest was not delayed in the C0.25m/T0.5m treatment in 2006 compared with the control and the double-tipped treatments; however, in 2007, harvest was delayed by 2 weeks in C0.25m/T0.5m. In contrast, harvest was delayed by ≈4 weeks when primocanes were cut to the ground at 0.5 m (C0.5m/T0.5m). Primocanes that were double-tipped produced heavier fruit than other treatments (33% heavier than the control, on average). Double-tipped primocanes did not have more ovules per flower, but had significantly more drupelets set compared with the control. In addition, plants growing under the tunnel tended to produce heavier fruit (32%, on average) than those grown in the open field. Harvest date affected fruit pH in 2006, but not in 2007. In 2006, fruit pH was highest in the early season. All other differences in fruit chemistry were not significant. The pruning and tipping systems used here increased yield and offered options for season extension.

Free access

Muscadine grapes (Vitis rotundifolia Michx.) are native to the southeastern United States and have potential for greater fresh-market sales if postharvest storage can be improved, but limited information is available on postharvest storability. In 2012 and 2013, physiochemical and storability attributes were measured in 17 muscadine genotypes (selections and cultivars) from the muscadine breeding program at the University of Arkansas or commercial cultivars. The postharvest and physiochemical attributes of the muscadines were measured at harvest and during storage for 3 weeks at 2 °C. Nutraceutical compounds were measured initially after harvest. As a result of extreme differences in weather in 2012 and 2013, the data were analyzed by year. Genotypes significantly affected storage attributes [weight loss (%), and unmarketable berries (%)] and physiochemical attributes such as penetration force (force to penetrate berry skin), titratable acidity (TA), pH, soluble solids (%), berry color (L*, chroma, and hue) as well as the nutraceutical compounds. The postharvest attributes of weight loss and unmarketable berries and the physiochemical attribute of penetration force were significantly affected by postharvest storage, but berry composition attributes remained fairly constant during storage. Overall, University of Arkansas selections AM 04, AM 26, AM 28, and the cultivar Southern Jewel had the highest potential for postharvest storage, whereas the genotypes AM 01, AM 15, AM 18, and ‘Nesbitt’ had the least potential. Genotypes AM 03, AM 04, AM 27, and ‘Ison’ had the highest nutraceutical contents [total anthocyanins, total phenolics, total flavonols, resveratrol, and oxygen radical absorbance capacity (ORAC)], whereas AM 18, AM 28, ‘Supreme’, and ‘Tara’ had the lowest contents. Postharvest storage potential, berry composition, berry color, and nutraceutical content were genotype-specific, but commercially viable genotypes were identified that can provide genetic material for breeding programs and postharvest evaluation protocol for commercial use.

Free access

Cowpea is a leguminous and versatile crop which provides nutritional food for human consumption. However, salinity unfavorably reduces cowpea seed germination, thus significantly decreasing cowpea production. Little has been done for evaluating and developing salt-tolerant cowpea genotypes at germination stage. The objectives of this research were to evaluate the response of cowpea genotypes to salinity stress through seed germination rate and to select salt-tolerant cowpea genotypes. The seed germination rates under nonsalt condition and salinity stress (150 mm NaCl) were evaluated in 151 cowpea genotypes. Four parameters, absolute decrease (AD), the inhibition index (II), the relative salt tolerance (RST), and the salt tolerance index (STI) were used to measure salt tolerance in cowpea. The results showed that there were significant differences among the 151 cowpea genotypes for all parameters (P values <0.0001). The AD in germination rate was 5.8% to 94.2%; the II varied from 7.7% to 100%; the RST ranged from 0 to 0.92; and STI varied from 0 to 0.92. A high broad sense heritability (H2) was observed for all four parameters. High correlation coefficients (r) were estimated among the four parameters. PI582422, 09–529, PI293584, and PI582570 were highly salt tolerant at germination stage. In addition, genotypes from the Caribbean and Southern Asia exhibited better tolerance to salinity, whereas those from Europe and North America were the most salt-susceptible.

Free access

Breeding and release of new fresh-market blackberries (Rubus subgenus Rubus Watson) is vital for competitive markets to address evolving changes and production challenges. Physical, composition, and sensory attributes of six University of Arkansas (UA) System Division of Agriculture blackberry cultivars (Caddo, Natchez, Osage, Ouachita, Ponca, and Prime-Ark® Traveler) were evaluated to identify marketable attributes. The consumer sensory study (n = 81) had two elements: a visual evaluation of displayed blackberries and an appearance, tasting, and firmness evaluation of the six cultivars using a 9-point verbal hedonic liking scale and a 5-point just about right (JAR) scale. Consumers preferred large blackberries when presented with individual berries of varying sizes and clamshells filled with equal weights of small or large blackberries. The largest of the six cultivars, Natchez and Caddo, were scored favorably for size and shape. Consumers also preferred clamshells with little to no red drupelet reversion, a postharvest disorder where black drupelets on the blackberry turn red during or after cold storage. Consumers did not detect differences in the appearance or firmness of the cultivars and rated the firmness of all cultivars favorably on the JAR scale. The physical and composition attributes of the six cultivars were within commercially acceptable ranges (soluble solids = 9% to 10%, pH = 3.1–3.8, titratable acidity = 0.6% to 1.4%, and berry weight = 6–10 g). ‘Ponca’, ‘Osage’, ‘Caddo’, and ‘Natchez’ were all rated highly for sweetness, sourness, overall flavor, and overall impression. ‘Ponca’ was rated high for sweetness, overall flavor, and overall impression and had 10.4% soluble solids, 0.82% titratable acidity, and a 12.8 soluble solids/titratable acidity ratio. The identification of these marketability attributes of fresh-market blackberries will provide information to advance breeding efforts for fruit with commercial potential.

Open Access

A major limiting factor in fresh-market muscadine grape (Vitis rotundifolia Michx.) commercialization is fruit deterioration during storage. Research on table grapes has shown that field fungicide applications increase storability, but little is known of their effect on muscadines. The effect of field applications of fungicides on physicochemical attributes during postharvest storage and nutraceutical content at date of harvest was evaluated on five muscadine cultivars (Nesbitt, Southern Jewel, Summit, Supreme, and Tara) and four breeding selections from the University of Arkansas Fruit Breeding Program in 2012 and 2013. There were two field treatments (no fungicide and fungicide). For the fungicide treatment, alternating applications of two fungicides were applied to the vine at 14-day intervals during berry maturation. Fruit was harvested and physicochemical attributes including berry volume, titratable acidity (TA), pH, soluble solids (%), color (L, chroma, and hue), firmness (force to penetrate berry skins and flesh), storage weight loss (%), and unmarketable fruit (%) were evaluated every 7 days for 3 weeks. Whole muscadine berries were analyzed for nutraceutical content only for the date of harvest. As a result of less decay, less weight loss, and greater firmness during storage, AM 27, ‘Southern Jewel’, and ‘Supreme’ had the highest potential for postharvest storage, whereas AM 01, AM 15, and ‘Tara’ had the least potential. Nutraceutical content varied by genotypes; overall AM 27 had the highest nutraceutical content [sum of anthocyanins, total phenolics, flavonols, resveratrol, and oxygen radical absorbane capacity (ORAC)], whereas ‘Supreme’ and AM 28 had the lowest. Total anthocyanins were only found in the black genotypes and total phenolics and resveratrol were unaffected by fungicide treatment. Total ellagitannins varied among the fungicide treatments. Total flavonols were generally greater in the no fungicide treatments, whereas ORAC was generally greater with fungicide treatments. Year of study and genotype were determined to be major contributors as sources of variation. Although field fungicide applications did not affect all postharvest attributes and nutraceutical components, differences among genotypes and fungicide treatments did occur.

Free access