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Jonathan Magby, Gayle M. Volk, Adam Henk and Steve Miller

Thousands of apple trees were planted in Wyoming’s orchards and homesteads in the 1800s, many of which are still alive today. Unfortunately, cultivar identity of these trees has mostly been lost or obscured. The purpose of this research was to identify heritage apple cultivars in Wyoming using genetic fingerprinting (microsatellite) techniques and to use this information to make recommendations on candidate cold-hardy cultivars for specialty crop and breeding programs. Leaf samples were collected from 510 heritage apple trees from 91 sites in 19 locales across Wyoming. Known cultivars from the U.S. Department of Agriculture (USDA)–National Plant Germplasm System, Seed Savers Exchange, and Washington State University apple collections were used as standards to determine cultivar identities. Overall, 328 (64%) of the previously unidentified apples trees were identified to 47 known cultivars. Fifteen of these known cultivars comprised more than 80% of the samples that were identified, with all 15 of those cultivars developed in states and countries with average temperatures or winter conditions similar to Wyoming. Seventy-one of the heritage trees were identified as the Wealthy cultivar. Other commonly identified cultivars were Haralson, Patten’s Greening, Yellow Transparent, Northwestern Greening, and McMahon. It is likely that a combination of popularity and cultivar origin affected the choice of cultivars that were grown in Wyoming. Although most original Wyoming heritage apple trees are reaching the end of their life span, many surviving trees continue to produce fruit. This strongly suggests that despite lower resistance to certain pathogens than many modern cultivars, these heritage trees should be considered for use today. The results provide insights into possible cultivars that could be grown in Wyoming and also in other states with similar harsh growing conditions.

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Jack E. McCoy and Paul W. Bosland

Powdery mildew [Leveillula taurica (Lév.) Arn] is a fungus causing epidemics on chile peppers (Capsicum sp.) worldwide. It was first observed in New Mexico in the late 1990s and has been a reoccurring issue. During the 2017 growing season, environmental conditions were highly favorable for powdery mildew development and severe infection was observed. This provided a unique opportunity to identify novel sources of resistance in Capsicum to powdery mildew. In the present study, the incidence and severity of powdery mildew was evaluated for 152 chile pepper accessions comprising different cultivars and species. Major differences in disease severity and incidence were observed among the accessions. Of the 152 accessions, 53 were resistant, i.e., received a disease index (DI) score of ≤1. When examining across Capsicum species, 16 Capsicum annuum accessions, all 8 Capsicum baccatum, all 21 Capsicum chinense, 5 of 6 Capsicum frutescens, the Capsicum chacoense accession, and the Capsicum rhomboideum accession were resistant. These results provide several accessions with resistance that can be used in breeding programs. Especially important are the C. annuum resistant accessions, as this resistance can be more quickly incorporated into commercially important C. annuum cultivars as compared with interspecific hybridizations.

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Chengyan Yue, Jingjing Wang, Eric Watkins, Stacy A. Bonos, Kristen C. Nelson, James A. Murphy, William A. Meyer and Brian P. Horgan

An online survey was conducted to investigate the current practices of and challenges for turfgrass breeders and turfgrass seed distributors (or sales staff) in the United States. We found that turfgrass seed breeders rated producers/growers and consumers as more important parties compared with other interested parties. However, variations in ratings were found for breeders/distributors according to different program characteristics. The volume of seed sales of the species was the most highly rated technical consideration for both breeders and distributors. Compared with distributors, breeders considered the following technical factors more important than others: funding, labor, field trial performance, diversity in working priorities, availability of germplasms, scheduling, and staff training. Costs, followed by resource allocation and resource availability, were rated as the most challenging factors when breeders were implementing priorities. Our findings provide important insight regarding breeding and distribution practices and management in the turfgrass industry.

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Dave Llewellyn, Katherine Schiestel and Youbin Zheng

A greenhouse study was undertaken to investigate whether light-emitting diode (LED) technology can be used to replace high-pressure sodium (HPS) lighting for cut gerbera production during Canada’s traditional supplemental lighting (SL) season (November to March). The study was carried out at the University of Guelph’s research greenhouse, using concurrent replications of SL treatments within the same growing environment. LED (85% red, 15% blue) and HPS treatment plots were set up to provide equal amounts of supplemental photosynthetically active radiation (PAR) at bench level. This setup was used to assess the production of three cultivars of cut gerbera (Gerbera jamesonii H. Bolus ex Hook.f): Acapulco, Heatwave, and Terra Saffier. There were no treatment differences in SL intensity, with average SL photosynthetic photon flux density (PPFD) and daily light integral (DLI) of 55.9 µmol·m−2·s−1 and 2.3 mol·m−2·d−1, respectively. Flowers harvested from the LED treatment had a 1.9% larger flower diameter in ‘Acapulco’; 4.2% shorter and 3.8% longer stems in ‘Heatwave’ and ‘Terra Saffier’, respectively; and 7.7% and 8.6% higher fresh weights for ‘Acapulco’ and ‘Terra Saffier’, respectively, compared with flowers harvested from the HPS treatment. There were no differences in accumulated total or marketable flower harvests for any of the cultivars. The vase life of ‘Acapulco’ flowers grown under the LED treatment was 2.7 d longer than those grown under the HPS treatment, but there were no SL treatment effects on water uptake for any of the cultivars during the vase life trials. There were no SL treatment effects on specific leaf area for any of the cultivars. There were only minimal treatment differences in leaf, soil, and air temperatures. Cut gerbera crops grown with under LED SL had equivalent or better production and crop quality metrics compared with crops grown under HPS SL.

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Brianna L. Ewing, Gregory M. Peck, Sihui Ma, Andrew P. Neilson and Amanda C. Stewart

Hard cider production in the United States has increased dramatically during the past decade, but there is little information on how harvest and postharvest practices affect the chemistry of the resulting cider, including concentrations of organoleptically important flavanols. For 2 years we assessed fruit, juice, and cider from a total of five apple (Malus ×domestica Borkh.) cultivars in two experiments: sequential harvests and postharvest storage. Different cultivars were used in 2015 and 2016 with the exception of ‘Dabinett’, which was assessed in both years. There were no differences in polyphenol concentrations in cider made from fruit that was harvested on three separate occasions over a 4-week period in either 2015 or 2016. Fruit storage durations and temperatures had little influence on the chemistry when the experiment was conducted in 2015, but polyphenol concentration was greater after storage in the 2016 experiment. In 2016, total polyphenols in ‘Dabinett’ ciders were 51% greater after short-term storage at 10 °C and 67% greater after long-term storage at 1 °C than the control, which was not subjected to a storage treatment. In 2016, total polyphenols in ‘Binet Rouge’ ciders were 67% greater after short-term storage at 10 °C and 94% greater after long-term storage at 1 °C than the control. Although results varied among cultivars and harvest years, storing apples for longer periods of time and at warmer temperatures may be a strategy to increase polyphenol, particularly flavanol, concentrations in hard cider.

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Stephen S. Deschamps and Shinsuke Agehara

Black plastic mulch is used predominantly for winter strawberry (Fragaria ×ananassa Duch.) production in Florida because of its warming effects. However, black plastic mulch can increase heat stress during establishment, especially when growers advance planting dates (e.g., late September) to improve earliness. Consequently, we designed a new plastic mulch film that has a metalized center stripe with black shoulders. We hypothesized that metalized-striped mulch can minimize heat stress during establishment, while maintaining the warming effects of black mulch during winter. We conducted field trials over two seasons to evaluate black mulch, fully metalized mulch, and metalized-striped mulch using two cultivars differing in heat stress tolerance and fruit production patterns: ‘Florida Radiance’ and ‘Florida Beauty’. The effect of plastic mulch type on plant growth and yield was generally consistent across both seasons. Compared with black mulch, metalized-striped mulch reduced afternoon root-zone temperature (RZT) by up to 3.1 °C and reduced the duration of heat stress conditions (RZT > 30 °C) by 119 hours across October and November, but exhibited equivalent soil warming during winter. Yield increases by metalized-striped mulch compared with black mulch ranged from 19% to 34% in the early season (November–January), 6% to 20% in the late season (February–March), and 12% to 26% over the entire season. Statistical significance was detected for the 2016–17 early-season yield and when yield data were expressed on a weekly basis. Compared with black mulch, metalized-striped mulch improved fruit number significantly without affecting fruit weight or canopy area, suggesting that heat stress on black mulch negatively affects flower and fruit development more than plant growth. Weekly fruit yield data indicate that metalized-striped mulch can produce greater yields than fully metalized mulch. Metalized-striped mulch is an easily implementable strategy for reducing establishment heat stress and improving fruit earliness in subtropical winter strawberry production regions.

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Yaser Hassan Dewir, Abdulhakim A. Aldubai, Rashid Sultan Al-Obeed, Salah El-Hendawy, Mayada Kadri Seliem and Khadija Rabeh Al-Harbi

Plant tissue culture offers opportunities for the rescue and conservation of endangered plant species. Here, we report the successful in vitro propagation of Dracaena ombet, an endangered plant. Several physical and chemical seed treatments were evaluated to develop a propagation approach. Germination of D. ombet seeds was monitored for 16 weeks by placing them onto Murashige and Skoog (MS) medium. Maximum seed germination (20%) was recorded when seeds were soaked-scarified, whereas all other treatments did not result in seed germination. Fragmented (longitudinally bisected) and intact in vitro shoots were cultured onto MS medium supplemented with various concentrations of 6-benzylaminopurine (BAP) and indole butyric acid (IBA) to induce axillary shoots. Longitudinal fragmentation of explants had a greater effect than the intact explants for shoot proliferation when cultured onto medium containing plant growth regulators. Fragmented shoots cultured onto MS medium supplemented with 2 mg·L−1 BAP and 0.5 mg·L−1 IBA treatment resulted in the highest amount of axillary shoots (seven shoots per explant). The intact shoots had the highest axillary shoots (1.8 shoots per explant) when cultured onto a medium supplemented with a combination of 1 mg·L−1 BAP and 0.5 mg·L−1 IBA. One hundred percent rooting was obtained using half strength MS medium supplemented with 0.5 or 1 mg·L−1 IBA. With full strength MS medium, a maximum rooting of 60% was obtained with 1 mg·L−1 IBA or naphthalene acetic acid (NAA) addition. The plantlets were acclimatized to ex vitro conditions with a 95% survival rate. This study offers a simple method for in vitro propagation of D. ombet, which is valuable to enable conservation of this endangered species.

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Dao-Jing Wang, Jing-Wen Zeng, Wen-Tao Ma, Min Lu and Hua-Ming An

Rosa roxburghii Tratt (Rosaceae) of various organ surfaces are widely existing trichomes. Certain varieties have fruits that are thickly covered with macroscopic trichomes. R. roxburghii Tratt (RR) and R. roxburghii Tratt. f. esetosa Ku (RRE) are important commercial horticultural crops in China because of their nutritional and medicinal values. RRE is generally considered a smooth-fruit variant that arose from RR. Despite their economic importance, the morphological and anatomic features of organ trichomes have not been explored in detail for these two rose germplasms. In this research, we investigated the distribution, morphology, and structure of trichomes distributed on the stem, pedicel, fruit, sepal, and marginal lobule sepals (MLS) of RR as well as RRE. This was accomplished using scanning electron microscopy (SEM). There are various shapes of trichomes distributed on the surfaces of stems, pedicels, fruits, and sepals of the two germplasms. Binate prickles arose on the stem nodes in both germplasms, but acicular trichomes, papillary trichomes, and ribbon trichomes were present only on the surfaces of pedicels in RR. Likewise, flagelliform trichomes were present only on the surfaces of pedicels in RRE. Furthermore, a transection of stems shows that thorns in the two germplasms are composed of epidermis, meristematic layer, and parenchyma cells. The trichome epidermis and meristematic layer in stems of RR are composed of round cells, whereas RRE exhibits square cells in the same layers. Trichomes on the fruit of RR were macroscopic and of single flagelliform and acicular shape. RRE exhibited polymorphic trichomes of flagelliform, triangular, capitate glandular, and elliptic glandular shapes on the pericarp. On the surfaces of RR sepals, there are thick macroscopic acicular trichomes. In contrast, RRE sepals presented flagelliform trichomes and capitate glandular trichomes. It is interesting that no trichomes were found on the surfaces of the MLS in the two germplasms; however, stomata were densely packed on the MLS of RRE when compared with RR. For RR, the trichomes on both sepal and fruit are composed of an epidermis layer and parenchyma cells; however, the epidermis cells of sepal trichomes are polygon-shaped, in contrast to the round epidermis cells in fruit. These results suggest that the two rose germplasms are good candidates for understanding the trichome ontogeny in the genus and for further breeding of the smooth organ trait in this rose species.

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny and Carolyn Scagel

Plant growth, water use, photosynthetic performance, and nitrogen (N) uptake of ‘Merritt’s Supreme’ hydrangea (Hydrangea macrophylla) were investigated. Plants were fertilized with one of five N rates (0, 5, 10, 15, or 20 mm from NH4NO3), irrigated once or twice per day with the same total daily amount of water, and grown in either a paper biodegradable container or a traditional plastic container. Greater N rate generally increased plant growth index (PGI) in both plastic and biocontainers. Leaf and total plant dry weight (DW) increased with increasing N rate from 0 to 20 mm and stem and root DW were greatest when fertilized with 15 mm and 20 mm N. Plants fertilized with 20 mm N had the greatest leaf area and chlorophyll content in terms of SPAD reading. Container type had no influence on DW accumulation or leaf area. N concentrations (%) in leaves, roots, and the entire plant increased with increasing N rate. N concentrations in roots and in the entire plant were lower in biocontainers compared with plastic containers. Greater N rate generally increased daily water use (DWU), and biocontainers had greater DWU than plastic containers. The 20 mm N rate resulted in the highest net photosynthetic rate measured on 11 Sept. and 22 Sept. (65 and 76 days after treatment). Net photosynthetic rate (measured on 8 Oct.) and stomatal conductance (g S) (measured on 27 Aug., 22 Sept., and 8 Oct.) were lower in biocontainers compared with plastic containers. Two irrigations per day resulted in higher substrate moisture at 5-cm depth than one irrigation per day, and slightly increased PGI on 19 Aug. However, irrigation frequency did not affect photosynthetic rate, g S, or N uptake of hydrangea plants except in stems. Considering the increased water use of hydrangea plants when grown in the paper biocontainer and lower plant photosynthesis and N uptake, the tested paper biocontainer may not serve as a satisfactory sustainable alternative to traditional plastic containers.

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Daniel Leskovar and Yahia A. Othman

The impact of nitrogen application on the growth of olive trees has been well studied. However, little is known about the role of levels and forms of N on the development of roots and physiological traits during establishment of young trees. The objective of this 2-year study was to evaluate the influence of N source and level on shoot morphology (tree height, stem diameter, and branch number) and physiology [leaf area and fresh weight, photosynthesis (Pn), transpiration (E), and stomatal conductance (g s)], root components (length, diameter, surface area, and fork number) and N content of young olive (Olea europaea cv. Arbequina) cuttings. Three-month-old olive cuttings were planted in 15-L pots filled with a growing substrate composed of peatmoss + bark + sand (2:1:1/by volume) and placed in a screen house. Two N levels, 2.8 and 5.6 g/tree, and control (0 N) and four N sources, calcium nitrate (CN, 12%N, 17%Ca+2), ammonium nitrate (AN, 35%N), urea (46%N), and the slow-release Osmocote (OSC, 18%N, 6%P, 12%K) were evaluated. Effects of low– (2.8 g/tree) and high N (5.6 g/tree) levels on shoot components (plant height, diameter, branch number, leaf area, and fresh weight) and gas exchange (Pn, g s and E) were similar implying that the low rate of N was adequate for the establishment of young olive cuttings. Nitrogen sources, particularly AN and CN had significant effects on shoot and root morphology, physiology, and leaf and root N concentration. In fact, AN and CN were the best fertilizer sources for olive transplants in term of root and shoot growth. Overall, 2.8 g/tree N level and AN or CN sources were the best treatments for newly established olive ‘Arbequina’ trees. Root components treated with high N rate (5.6 g/tree N) using the slow-release fertilizer (OSC) was similar to those treated with the low AN rate (2.8 g/tree N). Therefore, for nursery containerized olive trees of ‘Arbequina’ or other cultivars with comparable growth rates, we recommend to apply the CN or AN source at 2.8 g/tree N or the controlled-released fertilizer OSC at 5.6 g/tree N.