Porterweed (Stachytarpheta spp.), a member of the verbena family, is frequently used in pollinator gardens to attract butterflies. This study was conducted to assess the morphological features, pollen stainability and morphology, nuclear DNA content, and chromosome number of five porterweed selections. Coral porterweed (S. mutabilis), ‘Naples Lilac’ porterweed (S. cayennensis × S. mutabilis ‘Violacea’), and nettleleaf porterweed (S. cayennensis) had the largest plant heights. Flower number was significantly higher in nettleleaf porterweed, jamaican porterweed (S. jamaicensis), and U*J3-2 porterweed (S. cayennensis × S. jamaicensis), with an average of 65–72 flowers per inflorescence. Internode length and flower width of jamaican porterweed had much lower values than the other selections. Coral porterweed recorded the lowest pollen stainability with only 10.6% stainability, but it had the largest relative pollen production. ‘Naples Lilac’ porterweed had the highest DNA content with an average of 3.79 pg/2C, like jamaican porterweed with 3.73 pg/2C. Ploidy levels varied between selections, and the basic chromosome number was x = 28. Coral, jamaican, and ‘Naples Lilac’ porterweed had 2n = 6x = 168 chromosomes, first reported in this genus. These results provide a guide and a new tool to distinguish native and non-native porterweed and may aid future breeding toward the production of noninvasive cultivars.
Renjuan Qian, S. Brooks Parrish, Sandra B. Wilson, Gary W. Knox, and Zhanao Deng
M. Lenny Wells
A better understanding of the efficacy of various nitrogen (N) forms on pecan tree production would help growers make more sound decisions regarding the fertilization of their orchards. The following treatments were evaluated for their effect on pecan leaf tissue nutrient concentration, leaf chlorophyll index, trunk circumference growth, pecan yield, nut weight, percent kernel, pecan tree yield efficiency, and alternate bearing: 1) ammonium nitrate (AN; 34N–0P–0K) at 1.8 kg N per tree (AN1.8); 2) AN (34N–0P–0K) at 3.6 kg N per tree (AN3.6); 3) ammonium sulfate (AS) at 1.8 kg N per tree (AS1.8); 4) AS at 3.6 kg N per tree (AS3.6); 5) urea at 1.8 kg N per tree (U1.8); 6) urea at 3.6 kg per tree (U3.6); and 7) untreated control (C). Leaf elemental tissue analysis, pecan tree trunk growth, pecan yield, quality, and alternate bearing intensity (I) suggest that pecan trees are unaffected by differences in the fertilizer sources used in this study on the acidic soils of the Southeastern U.S. Coastal Plain. N rate also had little influence on measured variables. Based on these results and, perhaps more directly, upon agronomic N use efficiency (AE N), it appears that pecans can be more efficiently fertilized at N rates of 108 kg N/ha compared with 215 kg N/ha under Southeastern U.S. Coastal Plain conditions regardless of N source.
Jennifer K. Boldt and James E. Altland
Silicon (Si) is a plant-beneficial element that can alleviate the effects of abiotic and biotic stress. Plants are typically classified as Si accumulators based on foliar Si concentrations (≥1% Si on a dry weight basis for accumulators). By this definition, most greenhouse-grown ornamentals are low Si accumulators. However, plants that accumulate low foliar Si concentrations may still accumulate high Si concentrations elsewhere in the plant. Additionally, screening cultivars for variability in Si uptake has not been investigated for low Si accumulator species. Therefore, the objective of this study was to assess cultivar variability in Si accumulation and distribution in petunia (Petunia ×hybrida). Eight cultivars (Supertunia Black Cherry, Supertunia Limoncello, Supertunia Priscilla, Supertunia Raspberry Blast, Supertunia Royal Velvet, Supertunia Sangria Charm, Supertunia Vista Silverberry, and Supertunia White Improved) were grown in a commercial peat-based soilless substrate under typical greenhouse conditions. They were supplemented with either 2 mm potassium silicate (+Si) or potassium sulfate (-Si) at every irrigation. Silicon supplementation increased leaf dry mass (4.5%) but did not affect total dry mass. In plants not receiving Si supplementation, leaf Si ranged from 243 to 1295 mg·kg−1, stem Si ranged from 48 to 380 mg·kg−1, flower Si ranged from 97 to 437 mg·kg−1, and root Si ranged from 103 to 653 mg·kg−1. Silicon supplementation increased Si throughout the plant, but most predominantly in the roots. Leaf Si in the 2 mm Si treatment ranged from 1248 to 3541 mg·kg−1 (173% to 534% increase), stem Si ranged from 195 to 654 mg·kg−1 (72% to 376% increase), flower Si ranged from 253 to 1383 mg·kg−1 (74% to 1082% increase), and root Si ranged from 4018 to 10,457 mg·kg−1 (593% to 9161% increase). The large increase in root Si following supplementation shifted Si distribution within plants. In nonsupplemented plants, it ranged from 51.2% to 76.8% in leaves, 8.2% to 40.2% in stems, 2.8% to 23.8% in flowers, and 1.2% to 13.8% in roots. In Si-supplemented plants, it ranged from 63.5% to 67.7% in leaves, 10.5% to 22.6% in roots, 9.4% to 17.7% in stems, and 1.6% to 9.6% in flowers. This study indicates that petunia, a low foliar Si accumulator, can accumulate appreciable quantities of Si in roots when provided supplemental Si.
Sydney Lykins, Katlynn Scammon, Brian T. Lawrence, and Juan Carlos Melgar
The photosynthetic light response of commercial blackberry cultivars (Rubus L. subgenus Rubus Watson) is largely unexplored, although they are frequently grown in full sun. In this experiment, light response curves of floricane leaves from the cultivars Natchez, Apache, Navaho, and Von were examined throughout the following production stages: before shiny black fruit were present (before harvest, BH), during peak production of fruit (peak harvest, PH), and when most fruit had fallen from plants or any remaining were dull black (after harvest, AH). Each cultivar was evaluated between an irradiance of 2000 and 0 μmol·m–2·s–1. The estimated maximum photosynthetic rate (photosynthetic capacity, P Nmax) was greater BH than AH across all cultivars, whereas ‘Natchez’ had a greater P Nmax BH and PH compared with the other cultivars. During AH, all cultivars had a similar P Nmax. The BH response curves declined under the highest irradiance measured, whereas the PH and AH response curves remained stable at similarly high irradiance. Of the four cultivars, Apache, Navaho, and Von appeared to be more photosynthetically limited than Natchez under increasing irradiance. Based on the cultivar-specific performance observed, blackberry response to light is a relevant trait that breeding programs should consider for improving cultivar adaptability to local and regional conditions.
Bruno Casamali, Marc W. van Iersel, and Dario J. Chavez
New peach orchards in the southeastern United States are often not irrigated until 3 or 4 years after planting. During those years, the only water comes from rainfall. Droughts in the region are becoming more common, making irrigation more important. At the same time, fertilization practices follow recommendations developed decades ago and may not be optimal for current production practices. This research aimed to investigate the effect of different irrigation and fertilization practices on young ‘Julyprince’ trees grafted onto ‘Guardian™’ rootstock. The treatments consisted of irrigated vs. nonirrigated trees, drip- vs. microsprinkler-irrigated trees, and four different fertilizer levels (25%, 50%, 100%, and 200%; with 100% = current fertilizer recommendations). Responses to the treatments varied by year. In 2016, below-average rainfall (severe drought as classified by the U.S. Drought Monitor) was recorded throughout the year. This severe drought reduced the growth of nonirrigated trees compared with irrigated trees (average reductions of 56% in canopy volume, 39% in trunk cross-sectional area, 39% in leaf and stem water potential, and 40% in leaf photosynthesis). The adverse effects on tree growth and physiological responses of the 2016 season carried over to 2017, which was characterized by a short period of below-average rainfall in early spring. Nonirrigated trees displayed advanced budbreak progression; reduced commercial yield (10.9 vs. 13.4 kg/tree for nonirrigated vs. irrigated trees); and smaller trunk cross-sectional area (54.0 vs. 70.1 cm2) and canopy volume (8.9 vs. 10.9 m3) compared with irrigated trees. In 2018, rainfall was like the historical average throughout the year. Major differences continued to be trunk cross-sectional area (103.4 vs. 126.7 cm2) and canopy volume (15.8 vs. 17.8 m3), with nonirrigated trees being smaller than irrigated trees. No major or consistent differences were found between drip vs. microsprinkler irrigation or among fertilizer levels during the 3 years of the experiment. During the first years of orchard establishments, irrigation resulted in increased plant growth, commercial yield, and superior water status (higher values of water potential) compared with no irrigation, especially when rainfall was below the historical average. Although no major differences were found between the irrigation systems, drip irrigation used 35% less water than microsprinkler irrigation. While different fertilizer levels did not induce major differences in young trees’ growth and yield, potential economic savings and long-term effects of reduced fertilizer applications are being monitored as trees mature.
Qiannan Hu, Fei Ding, Mingna Li, Xiaxiang Zhang, Shuoxin Zhang, and Bingru Huang
Accelerated or premature leaf senescence induced by dark conditions could be associated with chlorophyll degradation and regulated by hormones. To study the effects of strigolactone (SL) on dark-induced leaf senescence and to examine the interaction effects of SL and ethylene on regulating dark-induced leaf senescence, plants of perennial ryegrass (Lolium perenne) exposed to darkness for 8 days were treated with a synthetic SL analogue (GR24), aminoethoxyvinyl glycine [AVG (an ethylene biosynthesis inhibitor)], or SL and AVG by foliar spray. Chlorophyll content, photochemical efficiency, electrolyte leakage, and ethylene production were measured. Expressions of genes associated with leaf senescence, SL biosynthesis and signaling, ethylene biosynthesis and signaling, and chlorophyll biosynthesis and degradation were determined. Foliar application of GR24 promoted leaf senescence in perennial ryegrass grown in darkness, and the intensity of action increased with the GR24 concentration. SL-accelerated leaf senescence was associated with the downregulation of four chlorophyll biosynthesis-associated genes and upregulation of four chlorophyll degradation-associated genes. AVG had functions counteractive to SL, suppressing dark-induced leaf senescence by downregulating chlorophyll degradation genes and SL synthesis genes. Our results suggested that SL and ethylene interactively regulated leaf senescence, mainly by controlling chlorophyll degradation induced by darkness in perennial ryegrass.
Qiuyue Ma, Shushun Li, Jing Wen, Lu Zhu, Kunyuan Yan, Qianzhong Li, Shuxian Li, and Bin Zhang
Acer truncatum seeds are an excellent source of beneficial natural compounds, including high levels of unsaturated fatty acids (UFAs), that promote health. Recently, A. truncatum has emerged as an oil crop. Therefore, the transcriptomes of A. truncatum seeds at 70, 85, 100, 115, 145, 180 days after flowering (DAF) were analyzed to gain a better understanding of the transcriptional and translational regulation of seed development and oil biosynthesis. A total of 28,438 genes were identified, and 3069/2636, 3288/3438, 1319/2750, and 5724/5815 upregulated/downregulated genes were identified when comparing different samples with 85 DAF seeds. Sixteen lipid metabolism pathways with 754 differentially expressed genes (DEGs) were identified, including 34 DEGs associated with UFA biosynthesis. A phylogenetic analysis revealed that six putative fatty acid desaturase (FAD) genes clustered into five FAD groups. A quantitative real-time polymerase chain reaction analysis indicated that the temporal expression patterns of oil biosynthesis genes and transcription factors were largely similar to the RNA sequencing results. The results of this study will enhance the current understanding of oil metabolism in A. truncatum seeds and allow new methods of improving oil quality and seed yield in the future.
Chao Zhou, Haide Zhang, Yixing Li, Fenfang Li, Jiao Chen, Debao Yuan, and Keqian Hong
The mechanism regulating procyanidin (PA) accumulation in banana (Musa acuminata) fruit is not understood. During this study, the effects of PA treatment on the activities of banana PA biosynthetic enzymes and transcriptomic profiles were investigated. The results showed that PA treatment delayed the decreases in leucoanthocyanidin reductase and anthocyanidin reductase activities, which affected the accumulation of PA. Furthermore, the peel samples of the control fruit and the PA-treated fruit on day 1 were selected for transcriptomic analysis. The results revealed that PA treatment induced 1086 differentially expressed genes. Twenty-one key genes, including those encoding biosynthetic enzymes and regulatory factors involved in PA biosynthesis, were validated using a quantitative real-time polymerase chain reaction. The results showed that these genes were upregulated by PA treatment during banana storage. Taken together, our study improves current understanding of the mechanism underlying PA-regulated banana senescence and provide new clues for investigating specific gene functions.