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Open access

Aidan Kendall, Travis R. Alexander, Gabriel T. LaHue, and Carol A. Miles

Mechanical hedging was evaluated at Washington State University Northwestern Washington Research and Extension Center, Mount Vernon, WA, in 2019 and 2020 on eight cider apple (Malus ×domestica) cultivars with four bearing habits: tip—Golden Russet, Harrison; spur—Brown Snout, Cap of Liberty; semispur—Tom Putt, Campfield; and crab—Puget Spice, Hewe’s Virginia Crab. Trees were planted on ‘Geneva 935’ (Malus hybrid) rootstock in one replicate block in 2014 and the second replicate block in 2016 and the central leader of all trees was headed in 2017 to equalize tree size and stage of development. Summer hedging was carried out on all cultivars on 16 July in 2019 and 7 July in 2020. The response of different cultivars was evaluated both years by measuring canopy area removed, shoot biomass removed, and fruit removed, and the amount of time to hedge was measured. Additionally, fruit diameter and fruit yield per tree were measured at harvest both years, and fruit weight was measured at harvest only in 2020. The hedger traveled at an average speed of 1.32 mph; it took 6 seconds on average to hedge both sides of one tree when in-row spacing was 6 ft and took 1.25 minutes to maneuver around the end of a row. The estimated time to hedge 1 acre was 1.45 hours when the hedger traveled at 116 ft/min and the orchard had 10 rows spaced 12 ft apart. Biomass removed on an area and weight basis was less in 2020 than in 2019, whereas yield per tree was 2.6 times greater in 2020 than 2019, and cultivars within a bearing habit differed in these responses to hedging both years. Fruit damaged by the hedger was assessed but observed to be negligible for all cultivars. Yield per tree was negatively correlated with fruit diameter (P < 0.001) and positively correlated with the number of fruit removed per tree (P < 0.025). Further research is needed to assess the long-term effects of hedging on biomass removal, yield, and biennialism to determine whether summer mechanical hedging is a cost-effective and suitable method for managing cider apple orchards.

Open access

Yang Sun, Wei Han, Xiuming Ma, Junfeng Wang, Guoqin Wei, and Jun Miu

Cherry leaf spot (CLS), caused by Passalora circumscissa, is a fungal disease that can cause decreased fruit quality and yield via inconsistent ripening or premature defoliation. Germplasm resource screening is the most reliable approach to disease control for economically important crops. However, information is limited in China about the resistance of cherry cultivars to leaf spot caused by P. circumscissa. The aim of this study was to identify the resistance levels of cherry cultivars. Fifty-two cherry cultivars, including 40 Prunus avium, four Prunus pseudocerasus, and eight Prunus cerasus cultivars were collected for resistance level characterization. These specimens were then used to screen for P. circumscissa resistance through both detached leaf assays and natural field infection. Significant differences in the disease index (DI) value among test cultivars, ranging from 5.7 (resistant) to 53.7 (highly susceptible) and 6.5 (resistant) to 53.2 (highly susceptible), were observed under the controlled and field conditions respectively. Correlation coefficients between DI in pairs of years were highly significant (0.77–0.86). Although resistance rankings for cherry cultivars between screening methods were variable, the resistance levels of 52 cultivars evaluated under controlled and field condition were comparable with a correlation coefficient of 0.70 (P < 0.01). The results indicated that, across cherry cultivars, responses to CLS in the detached leaf assay corresponded well to responses under field conditions. A detached leaf assay was developed as a complementary method to facilitate the screening of cherry cultivars for resistance to leaf spot caused by P. circumscissa. Our study provides a theoretical basis for cherry disease resistance breeding and rational cultivar utilization.

Open access

Jiarou Liu, Bo Wu, Tao Xie, Aiping Luan, Yaqi Ding, Zhichun Zhang, Yehua He, and Zhike Zhang

In natural conditions, it takes more than 3 years to complete the Ananas juvenile phase, and another 2 years for adult vegetative growth of the plantlet from in vitro buds. Ethylene has often been used to shorten the juvenile and vegetative phases to produce earlier flowering. It is important to induce in vitro flowering of Ananas plants to understand the flowering mechanism more completely, which is also related to flower organ differentiation and development as well as the pineapple fruit eye development. In this study, Murashige and Skoog (MS) basal medium was used to select the best combination for adventitious bud induction from the callus of Ananas bracteatus var. tricolor (A. tricolor). Flower induction from the callus was studied using 6-benzyladenine (6-BA) and 1-naphthylacetic acid (NAA) at four different concentrations (0, 1.0, 2.0, and 3.0 mg⋅L–1). Our results showed that when MS was added with 3 mg⋅L–1 6-BA and 2 mg⋅L–1 NAA under 2000 μmol⋅m–2⋅s–1 of light for 16 hours per day at a temperature of 20 °C, the callus of A. tricolor grew quickly, and adventitious buds were induced. After more than four successive subcultures (at day 80), differentiation of flower buds was observed on the aging callus tissue before a complete floral organ developed. This research could be used for the flowering regulation of Ananas plants in the future. Inducing flowers directly from the callus has important scientific significance for the differentiation and morphogenesis of Ananas plants.

Open access

Stephanie Rossi and Bingru Huang

Heat-induced leaf senescence has been associated with stress-induced oxidative damage. The major objective of this study was to determine whether exogenous application of β-carotene may improve heat tolerance in creeping bentgrass (Agrostis stolonifera cv. Penncross) by suppressing leaf senescence and activating antioxidant metabolism. Plants were subjected to heat stress at 35/30 °C (day/night) or at the optimal temperature of 22/18 °C (day/night), and were treated with either β-carotene (1 mm) or water (untreated control) by foliar spraying every 7 days for 28 days in controlled-environment growth chambers. β-Carotene application suppressed heat-induced leaf senescence, as demonstrated by an increase in turf quality (TQ) and leaf chlorophyll content as well as a reduction in electrolyte leakage (EL). β-Carotene-treated plants had a significantly lower malondialdehyde (MDA) content and significantly greater activity of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) from 14 through 28 days of heat stress, and ascorbate peroxidase (APX) activity from 21 through 28 days of heat stress. These findings suggest that β-carotene may promote heat tolerance by enhancing antioxidant activity to suppress leaf senescence.

Open access

Xiaotao Ding, Hongmei Zhang, Lizhong He, Haijun Jin, Qiang Zhou, Juan Yang, Weimin Zhu, Jizhu Yu, and Tingting Qian

To study and model changes in the development of pak choi (Brassica rapa ssp. chinensis Makino), three pak choi cultivars—Xinxiaqing No. 5 (Xinxiaqing 5), Haiqing, and Huawang—were grown in a modern greenhouse. Four structural parameters, including leaf length, leaf width, and plant height and width, were measured regularly every 3 days. The results showed that the changes in plant height and width, and leaf length and width of the three cultivars followed sigmoidal trends. Logistical regression models {Y = K/[1 + (KL 0)/L 0 × exp(–r × t)]; Y = K/[1 + (KL 0)/L 0 × exp(−r × rad)]} of the leaf length and width accumulated with growth days and with accumulated radiation fit the actual data very well, with the correlation coefficient R 2 all greater than 0.98. The R 2 values of the plant width accumulation models were all greater than 0.93, whereas the R 2 values of the plant height regression models were not robust. In this study, the regression models of changes in plant height and width, and leaf length and width of pak choi were used to study the changes of morphological characteristics and analyze the change rules of pak choi growth and development.

Open access

Peter J. Zale, Melissa K. McCormick, and Dennis F. Whigham

U.S. native temperate terrestrial orchids are of horticultural and conservation interest but are considered difficult to propagate from seed due to complex ecological requirements and a variable need for a mycorrhizal fungus. Although there has been significant research on germinating seeds and in vitro seedling development on a variety of temperate terrestrial orchid taxa from around the world, few studies have combined germination experiments with appropriate mycorrhizal fungi that support establishment and continued growth for purposes of ex situ collections development, conservation, or restoration. We conducted experiments with two species of asymbiotically propagated U.S. native orchids [Goodyera tesselata Lodd. and Platanthera blephariglottis (Willd.) Lindl.] to determine the effect of four substrates [Bog garden mix (peat:all-purpose sand) (B), New Zealand sphagnum (NZ), NZ sphagnum + 10% powdered tulip tree wood (NZ/W10), and NZ sphagnum + 50% powdered tulip tree wood (NZ/W50)] and whether inoculating with an appropriate mycorrhizal fungus grown on cellulose sorba rods would support orchid growth and survival in containers and subsequently in outdoor conditions. Morphological measurements and survival data were used in conjunction with real-time quantitative polymerase chain reaction to assess fungal abundance in containers and the impact of fungal presence on growth and survival characteristics. The addition of appropriate mycorrhizal fungi increased the growth and survival of both species across three (NZ, NZ/W10, and NZ/W50) of four substrates. The addition of a mycorrhizal fungus was not a universal solution to improving growth, but the addition resulted in increased abundance of the fungus and better plant performance. This novel experiment suggests that although addition of appropriate mycorrhizal fungi to orchids may increase performance, environmental and horticultural parameters also play an important role in successful orchid cultivation.

Open access

Dedang Feng, Hongying Jian, Hao Zhang, Xianqin Qiu, Zhenzhen Wang, Wenwen Du, Limei Xie, Qigang Wang, Ningning Zhou, Huichun Wang, Kaixue Tang, and Huijun Yan

Rose (Rosa L.) is an economically important ornamental genus that has been cultivated for its scent for the perfume industry since antiquity. However, most modern roses have lost their fragrance during the later stages of the breeding process. Here, 59 species of Rosa, including 24 wild Rosa species, 20 Chinese old garden roses, and 15 modern roses, were examined by headspace solid-phase microextraction and gas chromatography–mass spectrometry. Fifty-three volatile organic compounds (VOCs), including terpenoids, benzenoids/phenylpropanoids, and fatty acid derivatives, were detected with qualitative and quantitative analyses. Thirteen common components, including geraniol, citronellol, 2-phenylethanol, 3,5-dimethoxytoluene, 1,3,5-trimethoxybenzene, germacrene D, and cis-3-hexenyl acetate, were found. Furthermore, different wild species or cultivars showed different characteristic compounds. 3,5-Dimethoxytoluene and 1,3,5-trimethoxybenzene were the main compounds in Rosa odorata and Rosa chinensis, which are the original parents of modern roses. 2-Phenylethanol, citronellol, and geraniol were the main aromatic compounds in Rosa damascene and Rosa centifolia. Methyl salicylate, eugenol, methyl eugenol, and benzyl acetate were lost during domestication and breeding of wild Rosa species to Chinese old garden roses and then to modern cultivars. Geranyl acetate, neryl acetate, and dihydro-β-ionol were gained during this time and showed higher amounts across the rose breeding process. Natural and breeding selection may have caused volatile compound gains and losses. These findings provide a platform for mining scent-related genes and for breeding improved ornamental plants with enhanced flower characteristics to develop new essential oil–producing plants.

Open access

Andrea Myers, Anthony Gunderman, Renee Threlfall, and Yue Chen

Hand-harvesting parameters and postharvest marketability attributes of fresh-market blackberries (Rubus L. subgenus Rubus Watson) were characterized to develop a prototype for a soft-robotic gripper for robotic harvesting. A custom-made, force-sensing apparatus attached to the thumb and fingers of a person hand-harvesting blackberries was developed to quantify forces used to harvest and to identify appendages for harvesting. Four cultivars of blackberries grown in Arkansas were harvested at optimal ripeness and stored at 2 °C for 21 days to determine the impact on marketability attributes (leakage, decay, and red drupelet reversion). The forces during harvest imparted by the thumb and middle finger were greatest (0.77 N and 0.37 N, respectively), whereas the index and ring fingers used lower forces (0.16 N and 0.06 N, respectively), primarily to stabilize the blackberry. The forces applied to grab, stabilize, and harvest blackberries caused minimal marketability damage (leakage, <10%; decay, <2%; and red drupelet reversion, <8%) after postharvest storage. This project quantified harvest and postharvest parameters, allowing data-driven design of a three-prong soft-robotic gripper for harvest of fresh-market blackberries.

Open access

Rebekah C.I. Maynard and John M. Ruter

Salvia is a genetically diverse genus in the Lamiaceae family, with hundreds of species distributed globally. With base chromosome numbers ranging from 6 to 19 and ploidy levels ranging from diploid to octoploid, the genus has been proposed to be subdivided based on molecular data rather than morphology. However, little is known about total DNA content across the genus. The DNA content of 141 Salvia genotypes were analyzed using flow cytometry. Samples of Salvia were stained with propidium iodide and compared with the internal standards Pisum sativum ‘Ctirad’ and Solanum lycopersicum ‘Stupické’ to generate estimations of DNA content. Holoploid 2C genome sizes of the analyzed Salvia ranged from 0.63 pg to 6.12 pg. DNA content showed a wide distribution across chromosome number, ploidy, and clade. The wide distribution of DNA content across the genus further indicates the diversity of Salvia and may be useful for future breeding efforts.

Open access

Xiao-ting Li and Jian-ping Bao

In this study, the effects of different Xinjiang pear varieties and ‘Korla Fragrant Pear’ pollination on the stone cells and lignin of fruit were investigated. The contents of stone cells and lignin, and the activities of related enzymes [polyphenol oxidase (PPO), peroxidase (POD), and phenylalanine ammonium lyase (PAL)] were analyzed in fruit from different pollination combinations at different growth and developmental stages. Results showed that the stone cell mass density decreased rapidly at 60 to 90 days and 90 to 120 days after flowering. The stone cell and lignin contents, and activities of the three enzymes (PPO, POD, and PAL) decreased rapidly at 60 days after flowering. The stone cell mass density, stone cell and lignin contents, and enzyme activity of fruit from different pollination combinations varied at different timescales. The pear variety ‘Bayue‘ had the lowest stone cell and lignin contents in mature fruit from different pollination combinations. The stone cell content correlated positively with lignin content, stone cell mass density, and enzyme activity.