Many members of the citrus family (Rutaceae) are valued for the aromatic compounds emitted by their flowers. Ptelea species are unusually cold-hardy members of the Rutaceae, but conflicting descriptions of the fragrance of their unisexual flowers may discourage the use of these trees. We analyzed floral volatiles and human response to these chemicals to test the hypothesis that the fragrance of staminate and pistillate flowers of these species differs. Gas chromatography and mass spectrometry showed that most volatile chemicals emitted by flowers of Ptelea trifoliata and Ptelea crenulata are monoterpenes, sesquiterpenes, and esters. Most volatiles were emitted from flowers of both sexes, but ethyl benzoate and estragole were emitted only from pistillate flowers. When concentrations of aromatics differed between sexes, they were higher for pistillate flowers, except for cis-3-hexenyl butanoate and an unidentified terpene. For P. crenulata and P. trifoliata, respectively, 81% and 77% of survey responses were from volunteers who liked the fragrance. Panelists most frequently described the scent of flowers of P. crenulata of both sexes with the words citrus, lime, and sweet. Panelists distinguished between pistillate and staminate flowers of P. trifoliata, describing the odor of pistillate flowers most frequently with the words damp-earthy, spicy, and sweet; staminate flowers were perceived as light, fresh, grassy, and pleasant. This work represents the first analysis of floral volatiles of P. crenulata and resolves conflicting prior reports regarding the floral fragrance of P. trifoliata. We conclude that differences among people rather than the sex of flowers account for conflicting prior reports of floral fragrance. The scents of flowers of P. crenulata and P. trifoliata appeal to most people and are horticultural assets of these trees.
Anna J. Talcott Stewart, Terri Boylston, Lester Wilson, and William R. Graves
Chunxian Chen and William R. Okie
Peach (Prunus persica) cultivars maintained at the U.S. Department of Agriculture program at Byron, GA, have never been characterized with any molecular markers. In this study, 20 microsatellite markers were used to genotype 112 cultivars and the data were analyzed to discern their population structure and phylogenetic relationships. STRUCTURE simulations revealed four K clusters and broad genetic admixture among the cultivars. Principal coordinate analysis (PCoA) showed the cultivar groups from western, northeastern, and southeastern U.S. states were adjacent to each other except cultivars from Michigan (close to most southeastern state groups) and Florida (most distant from the other groups). Principal component analysis (PCA) showed that these cultivars had no obvious PCA partitioning boundaries. The intertwined distribution in both PCoA and PCA partitions suggested many of them were genetically closely related to each other largely because most shared same ancestral parentages. Most pairwise distance means within and between the cultivar groups were relatively low, suggesting close phylogenetic relations among those cultivars, as were demonstrated in the phylogenetic tree. Limiting factors and perspectives relevant to peach breeding are discussed.
Stephanie Rossi and Bingru Huang
Heat stress symptoms in cool-season plants are characterized by loss of chlorophyll (Chl) and membrane stability, as well as oxidative damage. The objectives of this study were to determine whether foliar application of β-sitosterol, a naturally occurring plant metabolite, may promote heat tolerance by suppressing heat-induced leaf senescence as indicated by the maintenance of healthy turf quality (TQ), and Chl and membrane stability; and to determine its roles in regulating antioxidant metabolism in creeping bentgrass (Agrostis stolonifera). ‘Penncross’ plants were exposed to heat stress (35/30 °C day/night) optimal temperature conditions (nonstressed control, 22/17 °C day/night) for a duration of 28 days in environment-controlled growth chambers. Plants were foliar-treated with β-sitosterol (400 µM) or water only (untreated control) before heat stress, and at 7-day intervals through 28 days of heat stress. Plants treated with β-sitosterol had significantly greater TQ and Chl content, and significantly less electrolyte leakage (EL) than untreated controls at 21 and 28 days of heat stress. Application of β-sitosterol reduced malondialdehyde (MDA) content significantly at 21 and 28 days of heat stress, and promoted the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) from 14 through 28 days of heat stress. β-Sitosterol effectively improved heat tolerance through suppression of leaf senescence in creeping bentgrass exposed to heat stress in association with the alleviation of membrane lipid peroxidation and activation of the enzymatic antioxidant system.
Ying Yang, Xian-Ge Hu, Bingsong Zheng, Yue Li, Tongli Wang, Anket Sharma, Huwei Yuan, and Jian-Feng Mao
MicroRNAs (miRNAs) are short noncoding RNAs (20–25 nucleotides) that regulate gene expression posttranscriptionally. However, identification and characterization of miRNAs remain limited for conifer species. In this study, we applied transcriptome-wide miRNAs sequencing to a conifer species Platycladus orientalis, which is highly adaptable to a wide range of environmental adversities, including drought, barren soil, and mild salinity. A total of 17,181,542 raw reads were obtained from the Illumina sequencing platform; 31 conserved and 91 novel miRNAs were identified, and their unique characteristics were further analyzed. Ten randomly selected miRNAs were validated by quantificational real-time polymerase chain reaction. Through miRNA target predictions based on psRNATarget, 2331 unique mRNAs were predicted to be targets of P. orientalis miRNAs that involved in 187 metabolic pathways in KEGG database. These targets included not only important transcription factors (e.g., class III homeodomain leucine zipper targeted by por-miR166d) but also indispensable nontranscriptional factor proteins (i.e., por-miR482a-3p regulated nucleotide-binding site leucine-rich repeat protein). Interestingly, six miRNAs (por-miR16, -miR44, -miR60-5p, -miR69–3p, -miR166b-5p, and -miR395c) were found in adaptation-related pathways (e.g., drought), indicating their possible involved in this species’ stress-tolerance characteristics. The present study provided essential information for understanding the regulatory role of miRNAs in P. orientalis and sheds light on their possible use in tree improvement for stress tolerance.
Ryan J. Hill, David R. King, Richard Zollinger, and Marcelo L. Moretti
Three 2-year field studies were conducted to evaluate 1-naphthaleneacetic acid (NAA) as a suppressant of suckers in European hazelnut (Corylus avellana L.). Treatments were basal-directed applications of NAA at 5, 10, and 20 g·L−1 a.i. applied once per season, and two sequential applications of NAA 10 g·L−1 a.i., 28 days apart, compared with 2,4-D (3.8 g·L−1 acid equivalent), and a nontreated control. Treatments were applied early in spring and repeated the following year. Both NAA and 2,4-D delayed sucker growth by 1.2- to 3.0-fold compared with the nontreated control, and response varied with experimental site and year. Sequential treatments of NAA significantly reduced sucker height and fresh weight 120 days after treatment. NAA applied in sequential treatments increased tree trunk cross-sectional area and canopy volume in two of the three experimental sites. Yield of hazelnuts increased when suckers were removed with NAA or 2,4-D compared with nontreated. Results indicate that NAA is an effective option to control suckers in hazelnuts and can help reduce herbicide and labor in sucker control.
Eric T. Stafne, Jenny B. Ryals, and Barbara J. Smith
White drupelet disorder (WDD) in blackberry (Rubus subgenus Rubus) is an abiotic condition resulting from a cultivar and environment interaction. Although high temperatures and light intensities have been implicated, little is known why this disorder manifests. Other factors, such as overall plant stress, may be contributing influences. In this study, three treatments were applied to examine whether the addition of nitrogen (N) can reduce WDD on ‘Sweetie Pie’ erect blackberry over three seasons. An initial 50 lb/acre (56.0 kg⋅ha–1) N was applied to all plots at budbreak. Two additional N application treatments of 100 kg⋅ha–1 were applied at one time (1×) or five, 20-kg⋅ha–1 applications (5×), spaced 1 week apart for 5 weeks starting at bloom. One control treatment of no additional N (0×) was also included. Berries were harvested and weighed as a total, then berries with white drupelets were separated out and weighed. The two values were divided to create a proportion and were then multiplied by 100 to determine the percentage. Nitrogen application decreased the percentage of white drupelet berries from 13.0% (control) to 10.0% (one additional application) and 9.1% (five additional applications). WDD for the 0× treatment correlated negatively to maximum high daytime temperatures during May (r = –0.58, P = 0.03) over the three seasons. Occurrence of white drupelets by treatments 0×, 1×, and 5× correlated significantly with the cumulative number of rainfall events (r = 0.49, 0.47, and 0.46, respectively). Leaf chlorophyll index and photosynthesis measurements were unaffected by treatment. Although it is likely that multiple factors are involved in the development of white drupelets, additional N may reduce the problem.
Lisa Wasko DeVetter, Suzette Galinato, Troy Kortus, and Jonathan Maberry
Floricane red raspberry (Rubus idaeus) produces biennial canes that are traditionally managed by annual selective removal of previously fruited floricanes and training of primocanes that will bear fruit in the next growing season. This process of pruning and training is labor intensive and costly, and growers would benefit from more economical methods of pruning and training. This 6-year project evaluated the economic viability of alternate-year (AY) production in a commercial floricane red raspberry field in northwest Washington and compared it to traditional, every-year (EY) production to assess whether the former could save costs. Despite savings from reduced chemicals, fertilizers, labor, general farm supplies, and other variable costs, the overall benefits of AY production were not enough to offset losses in revenue resulting from reduced yields under the conditions of this experiment in northwest Washington.
Gerardo H. Nunez and Mariana Neves da Silva
Hands-on activities are an essential part of horticulture education. However, facilitating hands-on activities in online horticulture courses is challenging partly due to a lack of literature that describes remote laboratories in the discipline. Here we describe our experience planning and executing a remote strawberry-growing activity in an online horticulture course at the University of Florida, Gainesville. Students received strawberry-growing kits that contained a strawberry (Fragaria ×ananassa) plant, substrate, and fertilizer. Instructions on growing the strawberry plant were delivered online and students had to provide weekly updates about the status of their plant for 5 weeks. At the end of the semester, students provided feedback about the hands-on activity in the form of an essay. Their answers were analyzed using text mining to gauge their perception of the activity. About 77% of students expressed positive sentiments about the remote activity including excitement, enjoyment, and knowledge gain. Students who expressed negative sentiments about the activity (≈23% of the total) focused on plant casualties and difficulties related to management practices. Overall, student essays and weekly updates reflected a relevant and engaging cognitive exercise in horticulture. Our results suggest that remote laboratories can improve the student experience in online courses and provide a footprint for successful implementation of similar activities in online horticulture courses.
Renata Goossen and Kimberly A. Williams
Hydrogen peroxide (H2O2) is a well-known oxidizing agent often used as a remedy by consumers to treat algae and root decay from presumed root disease on interior plants, as well as to encourage root growth and health. To characterize the phytotoxic effects and define the safe concentration threshold for H2O2 use on ‘Vivaldi’ hybrid phalaenopsis orchid (hybrid Phalaenopsis), root systems were dipped for 3 minutes in 0%, 3%, 6%, or 12% H2O2 one time and observed in greenhouse conditions for the following 27 days. Root systems of each plant were assessed over time for percent visible root damage; ratings of root health on a scale of 1 to 5 points, with 5 points indicating “very healthy”; and final fresh and dry weights. To determine when symptoms manifested above the root zone, foliage and flower damage was evaluated over time by assessing percent visible foliage damage, ratings of foliage health, percent foliar wilt, flower/bud count, and final foliage and flower fresh and dry weights. Over the evaluation period, the root health rating of the ‘Vivaldi’ hybrid phalaenopsis orchids treated with 12% H2O2 decreased from 5 to 1.13, whereas those treated with 3% H2O2 only decreased from 5 to 4.13. H2O2 concentrations of 6% and 12% damaged root health permanently, whereas the 3% H2O2 concentration only caused minor damage to overall root health. However, algae were not killed at the 3% rate. Neither foliage nor flowers were seriously affected during the 3 weeks after application, but foliage wilt did result in the 6% and 12% treatments by week 4. As H2O2 concentration increased, fresh weights decreased in roots and leaves. Although a single 3% H2O2 root dip did not result in severe symptoms of phytotoxicity, the treatment’s long-term plant health effects are unknown. Because the 3% H2O2 root dip caused minor plant health setbacks and failed to subdue algae populations in the root zone, consumers should be wary of using H2O2 to improve orchid (Orchidaceae) root health and should instead focus on altering care and watering practices.