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  • Author or Editor: He Zhang x
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Kalmia latifolia L. (mountain laurel), a member of Ericaceae, is a beautiful ornamental shrub native to the eastern United States. The plant is not common in the southeastern United States landscapes because of the limited heat tolerance of most commercial cultivars. Breeding of heat-tolerant cultivars can be achieved by cross hybridization, but is often challenged by low germination percentage, long germination time, and potential abortion of cross-hybridized seeds. We used in vitro seed germination to enhance germination and shorten germination time and investigated the appropriate collecting time, optimal basal medium, and pH for this approach. Collecting time affected in vitro seed germination, with more mature hybrid seeds [collected 4–5 months after pollination (MAP)] having higher germination rate (90% in 4 weeks) than the less mature seeds collected in 2 MAP (20% in 7 weeks). Seedlings from the mature seeds also produced two true leaves on average after 8 weeks of culture, whereas seedlings from the less mature seeds had no true leaves. Woody Plant Medium (WPM) better enhanced in vitro seed germination compared with Murashige and Skoog (MS) or Gamborg’s B5 (B5) medium. WPM yielded higher germination (98%) than MS (90%) and significantly greater total leaf area per seedling (67 mm3) than MS (50 mm3) and B5 (52 mm3) for seeds of ‘Firecracker’ × ‘Snowdrift’. Similar effects had been observed on seeds from ‘Little Linda’ × ‘Starburst’ and ‘Pristine’ × ‘Peppermint’. The pH ranging from 4.2 to 5.4 did not affect seed germination and seedling development of mountain laurel hybrids. Our protocol enabled early collection of mountain laurel hybrid seeds 1 month before their full maturation and permitted seeds to germinate in 4 weeks on WPM, which shortened the period from crossing to the seedling stage from up to 15 to 6 months and enhanced germination percentage from 30% to more than 90% compared with traditional seed germination. This protocol should be applied to promote the breeding and selection of new mountain laurel cultivars for the southeastern United States landscapes.

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Mountain laurel (Kalmia latifolia) is an outstanding ornamental shrub due to its attractive foliage and showy inflorescences. Breeding efforts have led to improved selections that have predominantly been developed and evaluated in the northeastern United States. Consequently, most cultivars have largely been dismissed as incompatible for the southeastern U.S. environmental conditions by nursery growers and consumers. This study was conducted over a 4-year period to evaluate 21 popular mountain laurel cultivars, primarily developed in the northeastern United States, for container and field performance in Georgia. All cultivars yielded considerable growth in the first year of container trials, indicating production of mountain laurel as a 1-year container crop is feasible. Cultivars displayed significantly different total growth index throughout the container trial. Fast-growing cultivars such as Bullseye and Ostbo Red yielded more than 100, 150, and 250 cm of growth index in 1, 2, and 4 years, respectively. Conversely, cultivars that grew slower, such as Firecracker and Tinkerbell, had less than 80, 115, and 180 cm in 1, 2, and 4 years, respectively. Cultivars were classified into five groups, using principal component analysis, that included dwarf habit with pink flower, dwarf habit with nonpink flower, nondwarf habit with green stem and white flower, nondwarf habit with pigment-patterned flower, and nondwarf habit with pink flower. In a field study, performance rating of 21 cultivars ranged from 2.0 to 4.8 (out of 5.0) in 2014 and from 2.0 to 5.0 in 2015. Ten cultivars that received the highest ratings over these 2 years were selected for a subsequent field trial in 2016. Cultivars showed overall decreased ratings (1.0–3.3) from the previous 2 years because of late spring planting. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ had higher performance ratings, more net growth, and less decrease in maximum quantum yield, which indicated suitable adaptation to southeastern U.S. environmental conditions. Nursery growers and consumers should benefit from regional cultivar trial information derived from this study. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ performed well across trials and therefore are recommended for southeastern U.S. landscapes based on superior container and field performance, leaf spot (caused by Mycosphaerella colorata) tolerance, and morphologic distinctions.

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Conventional crossbreeding remains an effective technique for chrysanthemum (Chrysanthemum ×morifolium Ramat.) breeding. However, there are always many problems when breeding chrysanthemum because of its complex genetic background, such as difficulty matching parents, selecting superior hybrid progenies, quantitatively describing certain target traits, and evaluating breeding results. A recent mathematical analysis method is an effective method for evaluating plant breeding progress. In this study, we used 505 multiflora chrysanthemum germplasm resources as test materials; we divided the flowering time into five groups using a grading analysis method, including extremely early group (genotypes that flowered when daylength was longer than 13.5 hours), early group (genotypes that flowered when daylength was 13.5–12.0 hours), medium group (genotypes that flowered when daylength was 12.0–11.0 hours), late group (genotypes that flowered when daylength was 11.0–10.0 hours), and extremely late group (genotypes that flowered when daylength was shorter than 10.0 hours). Moreover, the breeding objective was to breed early-flowering genotypes. Using 15 phenotypic characters as evaluation factors, 37 excellent genotypes, including four early-flowering genotypes, were screened out from the aforementioned resources according to an analytic hierarchy process (AHP) and weighting of the gray relational grade. We selected one early-flowering genotype and eight medium-flowering genotypes from these 37 genotypes and matched six hybridized combinations based on the genetic distance between genotypes calculated by the Q cluster analysis method. We used a comprehensive evaluation method combining AHP and the gray relational analysis (GRA) method for the evaluation of 367 progenies. Moreover, we screened out 52 superior hybrids, including 36 early-flowering hybrids. The results of this study demonstrate that the mathematical analysis method is an immensely effective method to breed new cultivars of early-flowering multiflora chrysanthemum. This study also provides an effective method to define and improve the flowering time of other cultivated plants.

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A study on multipass harvesting using a mechanical harvesting prototype was proposed for mechanical harvesting of fresh market sweet cherries. Fruit damage rate, fruit removal rate, and fruit maturity level were three of the measures used to compare the performance of the multipass harvesting method against single-pass harvesting. The multipass harvesting was conducted in four consecutive days with short duration of 2.5 seconds at each day, while the single-pass harvesting was one-time harvesting with long duration of 10 seconds at a single day. To generate baseline information for comparison, single-pass harvestings were performed on the first and the last days of the multipass harvesting. Fruit maturity level was determined by comparing the fruit skin color against a standard color chart with seven color levels. Field test results showed that the percentage of under-mature fruit (maturity levels ≤ 5) was substantially lower with multipass harvesting than that with day 1 single-pass harvesting. Similarly, the percentage of over-mature fruit (maturity level 7) was noticeably lower with multipass harvesting than that with day 4 single-pass harvesting. Multipass harvesting achieved a fruit removal rate of 83.4% ± 10.3% and a harvest-induced fruit damage rate of 5.0% ± 4.4%. The corresponding fruit removal rates from single-pass harvesting tests were 48.0% ± 16.1% on day 1 and 66.7% ± 16.2% day 4. Harvest-induced fruit damage rates with single-pass harvesting were 20.1% ± 9.9% on day 1 and 11.8% ± 6.0% on day 4. The results supported the hypothesis that multipass of short-duration shaking offer a potential to achieve a higher overall harvesting efficiency with better fruit quality, and therefore could lead to an optimal solution for mechanical harvesting of fresh market sweet cherries. It is noted that comprehensive economic analysis will be necessary to establish commercial viability of the system in comparison with single-pass solutions.

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Dendrobium officinale, endemic to China, is a rare and endangered medicinal herb. As a result of its high economic value, slow growth, and diminishing wild population, protected cultivation is preferred. However, little information is available on its growing environment and photosynthetic characteristics. In this study, the photosynthetic patterns of D. officinale were investigated under various environmental conditions by measuring the net CO2 exchange rates continuously for several days or weeks. Under non-stressed growth chamber conditions with 12-hour light and 12-hour dark periods, D. officinale had concomitance of C3 and crassulacean acid metabolism (CAM) photosynthesis patterns. Different degrees of CAM in D. officinale, expressed as the percentage of CO2 exchanges in the dark period to the daily amount of CO2 exchanges, were observed depending on environmental conditions. With decreasing substrate water content, a typical CAM pattern was found, and concomitance of C3 and CAM patterns was found again when plants were rewatered. The accumulation of leaf titratable acidity during a dark period increased as substrate dried out but decreased again as plants were rewatered. A shorter light–dark cycle (4-hour light and 4-hour dark periods) led to a C3 pattern alone. The substrate moisture and light–dark cycle were inducible factors for switching between C3 and CAM patterns in D. officinale. These results indicate that D. officinale is a facultative CAM plant and the C3 pathway can be induced by controlling the growing environment. Further studies are needed to identify the optimal environmental conditions to enhance the growth of D. officinale.

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Bletilla is an Orchidaceae genus with high medical value, including detumescence, antibacterial, and hemostasis. In this study, detailed estimates of ploidy level, karyotype, and genome size were first obtained, and a comprehensive cytological analysis was carried out to better understand the evolution of the genus. The karyotypes of Bletilla were mainly composed of metacentric and submetacentric chromosomes with lengths ranging from 1.25 to 4.93 μm. There was moderate cytological variation in Bletilla (chromosome number 2n = 32 to 76). Diploid with 2n = 34 and 2n = 36 was detected in Bletilla ochracea and Bletilla formosana, respectively, whereas diploid (2n = 32) was dominant in Bletilla striata, dysploidy (2n = 34, 2n = 36) and polyploid (2n = 48, 51, 64, 76) variations were also observed. Three species had a relatively symmetric karyotype, and which of B. ochracea was more asymmetry. The genome size (1C-values) varied from 2.94 pg (B. striata) to 3.33 pg (B. ochracea), of which B. ochracea was significantly larger than the others (P < 0.05). A positive correlation (P < 0.01) between 1Cx vs. haploid chromosome length (HCL) and asymmetry coefficient of karyotypes (AsK%) was observed.

Open Access

Plant growth and development are significantly affected by salt stress. Chrysanthemum lavandulifolium is a halophyte species and one of the ancestors of chrysanthemum (C. ×morifolium). Understanding how this species tolerates salt stress could provide vital insight for clarifying the salt response systems of higher plants, and chrysanthemum-breeding programs could be improved. In this study, salt tolerance was compared among C. lavandulifolium and three chrysanthemum cultivars by physiological experiments, among which C. lavandulifolium and Jinba displayed better tolerance to salt stress than the other two cultivars, whereas Xueshan was a salt-sensitive cultivar. Using the transcriptome database of C. lavandulifolium as a reference, we used digital gene expression technology to analyze the global gene expression changes in C. lavandulifolium seedlings treated with 200 mm NaCl for 12 hours compared with seedlings cultured in normal conditions. In total, 2254 differentially expressed genes (DEGs), including 1418 up-regulated and 836 down-regulated genes, were identified. These DEGs were significantly enriched in 35 gene ontology terms and 29 Kyoto Encyclopedia of Genes and Genomes pathways. Genes related to signal transduction, ion transport, proline biosynthesis, reactive oxygen species scavenging systems, and flavonoid biosynthesis pathways were relevant to the salt tolerance of C. lavandulifolium. Furthermore, comparative gene expression analysis was conducted using reverse transcription polymerase chain reaction to compare the transcriptional levels of significantly up-regulated DEGs in C. lavandulifolium and the salt-sensitive cultivar Xueshan, and species-specific differences were observed. The analysis of one of the DEGs, ClAKT, an important K+ transport gene, was found to enable transgenic Arabidopsis thaliana to absorb K+ and efflux Na+ under salt stress and to absorb K+ under drought stress. The present study investigated potential genes and pathways involved in salt tolerance in C. lavandulifolium and provided a hereditary resource for the confinement of genes and pathways responsible for salt tolerance in this species. This study provided a valuable source of reference genes for chrysanthemum cultivar transgenesis breeding.

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The addition of pulverized grape pruning wood to grape soils has a positive effect on fruit quality. However, its effects on the soil microecology of the root zone and the growth of the grape plants are not fully understood. To address this, ‘Shine Muscat’ grapes were cultivated in media consisting of garden soil and crushed grape pruning material at different mass ratios [100:1 (T1), 50:1 (T2), 30:1 (T3), 20:1 (T4), and 10:1 (T5)] and in garden soil without the pruning material, as a control. The changes in the plant fresh weight, leaf area, soil and plant analyzer development (SPAD) value, root development, soil organic carbon, microbial biomass carbon, and soil enzyme activity were determined over time. High-throughput sequencing technology was used to determine the soil bacterial community structures. The pruning supplementation increased the grape plants fresh weight, leaf area, and SPAD values. The T2 and T3 treatments increased the grape root length, surface area, and the projected area and number of the root tips; the soil organic carbon content, microbial biomass carbon content, soil invertase activity, amylase activity, and β-glucosidase activity were also significantly increased. The addition of the grape pruning material was found to increase the bacterial diversity and richness 60 and 150 days after treatment. At the phylum level, Proteobacteria, Acidobacteria, and Actinobacteria were the dominant groups, and the grape pruning material increased the relative abundance of the Acidobacteria and Actinobacteria after 60 and 150 days. The relative abundance of the Actinobacteria in the T2 treatment was 1.7, 1.3, 1.5, and 1.3 times that of the control, after 60, 90, 120, and 150 days, respectively. The T2 treatment was identified as the optimal treatment for grapes in the field because it improved the soil microecology and promoted root and tree development the most compared with the other treatments tested.

Open Access

GA20-oxidase (GA20-ox) is a key enzyme involved in the biosynthesis of gibberellic acid (GA). To investigate its role in plant growth and development, we suppressed MdGA20-ox gene expression in apple (Malus domestica cv. Hanfu) plants by RNA interference (RNAi). After 20 weeks of growth in the greenhouse, significant phenotype differences were observed between transgenic lines and the nontransgenic control. Suppression of MdGA20-ox gene expression resulted in lower plant height, shorter internode length, and higher number of nodes compared with the nontransgenic control. The expression of MdGA20-ox in transgenic plants was significantly suppressed, and the active GA content in transgenic lines was lower than that in the nontransgenic control. These results demonstrated that the MdGA20-ox gene plays an important role in vegetative growth, and therefore it is possible to develop dwarfed or compact scion apple cultivars by MdGA20-ox gene silencing.

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