Citrus Huanglongbing (HLB, also known as “citrus greening”), an important disease worldwide, is associated with three species of phloem-limited Candidatus liberibacter, of which Candidatus L. asiaticus (CLas) is the predominant one that has severely affected citrus production. TaqMan real-time polymerase chain reaction (PCR) (TM) has been the standard and very efficient method to diagnose several strains of Candidatus Liberibacter in citrus; however, it detects total bacteria and is unable to differentiate dead from live Liberibacter. The detection of only live bacteria is essential for testing methods of control for this important citrus disease. It is well known that ethidium monoazide and propidium monoazide (PMA) are compounds that supposedly enter only dead or membrane-damaged bacteria, intercalate the DNA strand, and make the DNA unavailable for amplification by PCR. These compounds are widely used when extracting the plant DNA to detect only live bacteria. In this research, we tested primers amplifying products from 79 to 1160 bp in TM and SYBR Green real-time PCR (SG) and PMA as DNA intercalating compound. Specifically, primers amplifying a 500-bp amplicon in SG provided the most reliable live-only detection, whereas those producing a smaller amplicon were unable to distinguish between live and dead. This is the first report of testing primers amplifying various amplicon sizes for the detection of only live CLas cells in citrus.
Eliezer Louzada, Omar Vazquez, Sandy Chavez, Mamoudou Sétamou, and Madhurababu Kunta
Nathan J. Jahnke, Jennifer Kalinowski, and John M. Dole
Huihui Xu, Xi Wang, Xiaojuan Liu, Yingchao Li, Libing Wang, Haiyan Yu, and Quanxin Bi
Young-Sik Park, Je-Chang Lee, Haet-Nim Jeong, Nam-Yong Um, and Jae-Yun Heo
Paul C. Bartley III, William C. Fonteno, and Brian E. Jackson
The physical, hydrological, and physico-chemical properties of horticultural substrates are influenced by particle shape and size. Sieve analysis has been the predominate method used to characterize the particle size distribution of horticultural substrates. However, the literature shows a diversity of techniques and procedures. The effects of agitation time and sample size on particle size distributions of soilless substrates were evaluated for several measures of sieve analysis, including sieve rate (a calculation of the percentage of material passed for each unit time of agitation), distribution median, sd, mass relative span, skewness, and kurtosis. To obtain the standard sieve rate (0.1%/min), pine bark, peat, perlite, and coir required agitation times of 4 minutes and 47 seconds, 7 minutes and 18 seconds, 10 minutes, and 11 minutes, respectively. However, there was concern that unwanted particle breakdown may occur during the particle size analysis of some materials. Therefore, a sieve rate (0.15%/min) for more friable materials was also determined. As a result, the endpoint of sieving was reached sooner for pine bark, peat, perlite, and coir, at 3 minutes and 10 seconds, 4 minutes and 42 seconds, 5 minutes and 14 seconds, and 6 minutes and 24 seconds, respectively. Increasing agitation time resulted in decreased distribution median, sd, and skewness for all materials. Sample sizes half and twice the volume of the recommended initial volume sieved did not change particle size distributions. For more precise characterization of particle size distributions when characterizing substrate components, agitation times and sample sizes should be specified for each material or collectively for all materials to ensure consistency and allow comparisons between results.
Shih-Han Hung, Chia-Ching Wu, Yu-Chen Yeh, Ang Yeh, Chun-Yen Chang, and Hsing-Fen Tang
Nature and health researchers have often suggested that nature induces better psychological and physical health responses than urban environments, especially with healthy ecosystems in nature. However, research that has empirically documented the daily benefits of physical and psychological health in rural landscapes is scarce. This study explores how rural landscapes could provide better health benefits than the built environment in daily life. The research involved on-site data collection with a set of psychological indicators (e.g., restorativeness, preference, emotion) and physical indicators (e.g., brain waves, heart rate) to compare the rural and the built environments. A total of 169 subjects took part in the study. We analyzed health indicators through analysis of variance to show the difference in water landscapes in rural areas relative to the built environment after the participants experienced the environments. The results showed that subjects could release stress and felt a greater sense of restorativeness, pleasure, and arousal in rural areas than in the built environment. Subjects preferred the rural landscape more than the built environment. To conclude, this study explains the rural landscape and its health-related benefits in Taiwan.
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.
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.
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.
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.