In fruit trees, flowering is a key event followed by fruit development and seed production. Gigentea (GI), a clock-associated gene, is known to contribute to photoperiodic flowering and circadian clock control in Arabidopsis thaliana. However, its functions in woody fruit trees remain unclear. In this study, a 2000 bp promoter fragment of the longan (Dimocarpous longan) DlGI gene was isolated from the genomic DNA of longan ‘Honghezi’ by polymerase chain reaction amplification. The DlGI promoter contained two main types of potential cis-acting elements: light-responsive and hormone-responsive elements. The promoter was fused with the β-glucuronidase (GUS) reporter gene of pBI121 to generate the pDlGI:GUS construct. GUS histochemical staining of transgenic A. thaliana revealed that DlGI might play a role in different developmental phases of longan. Exposure of transgenic A. thaliana to varying light intensities showed that the GUS activity increases with increased light intensity. Transient expression of pDlGI::GUS in Nicotiana benthamiana showed that the GUS activity was higher and reached peak a few hours earlier under short-day (SD) than long-day conditions. Exposure to different hormonal treatments revealed that the transcript level of GUS was activated by gibberellin (GA3) and indoleacetic acid (IAA) but suppressed by abscisic acid and methyl jasmonate treatment. In addition, N. benthamiana transient assay and dual-luciferase assay revealed that the presence of early flowering 4 (ELF4) homologs of longan (DlELF4-1 and DlELF4-2) significantly activated the DlGI promoter. The positive response of DlGI promoter to high light-intensity, SD photoperiod, GA3 and IAA signals, and DlELF4 transcription factor suggest that DlGI may function as a circadian clock and play a role in responding to SD conditions and other signals in flower initiation of longan.
Saquib Waheed, Yuan Peng, and Lihui Zeng
This supplement contains the abstracts of presentations from the following National Conference and Regional Meetings of the American Society for Horticultural Science
Lauren Fessler, Amy Fulcher, Dave Lockwood, Wesley Wright, and Heping Zhu
Advanced variable-rate spray technology, which applies pesticides based on real-time scanning laser rangefinder measurements of plant presence, size, and density, was developed and retrofitted to existing sprayers. Experiments were conducted to characterize the application of four programmed spray rates (0.03, 0.05, 0.07, or 0.09 L·m−3 of crop geometric volume) when applied to Malus domestica Borkh. ‘Golden Delicious’ apple trees using this crop sensing technology. Water-sensitive cards (WSCs) were used as samplers to quantify spray coverage, deposits, and deposit density in the target and nontarget areas, and an overspray index based on a threshold of greater than 30% coverage was calculated. The application rate ranged from 262 L·ha−1 at the programmed spray rate of 0.03 L·m−3 to 638 L·ha−1 at the rate of 0.09 L·m−3. For a given WSC position, spray coverage and deposits increased as the spray rate increased. WSC positions 1 and 2 were oversprayed at all rates. The effect of spray rate on deposit density varied with WSC positions, with high densities achieved by low spray rates for WSCs closest to the sprayer but by high spray rates for WSCs positioned either deeper within or under the canopy. When coalescing deposits were accounted for, deposit densities met or exceeded the recommended pesticide application thresholds (insecticides 20–30 droplets/cm2; fungicides 50–70 droplets/cm2) at all WSC positions for each spray rate tested. The lowest spray rate reduced off-target loss to the orchard floor by 81% compared with the highest rate, dramatically reducing potential exposure to nontarget organisms, such as foraging pollinators, to come into contact with pesticide residues. Applying the lowest rate of 0.03 L·m−3 met deposit density efficacy levels while reducing spray volume by 83% compared with the orchard standard application of 1540 L·ha−1 and by 87% compared with the 1950 L·ha−1 application rate recommended when using the tree row volume method. Thus, there is potential for growers to refine pesticide application rates to further achieve significant pesticide cost savings. Producers of other woody crops, such as nursery, citrus, and grapes, who use air-assisted sprayers, may be able to achieve similar savings by refining pesticide applications through the use of laser rangefinder-based spray application technology.
Yanxia Zhao, Guimei Qi, Fengshan Ren, Yongmei Wang, Pengfei Wang, and Xinying Wu
Abscisic acid (ABA) is an essential phytohormone that regulates plant growth and development, particularly in response to abiotic stress. The ABA receptor PYR/PYL/RCAR (PYL) family has been identified from some plant species. However, knowledge about the PYL family (VvPYLs) in grape (Vitis vinifera) is limited. This study aims to conduct genome-wide analyses of VvPYLs. We successfully identified eight PYL genes from the newest grape genome database. These VvPYLs could be divided into three subfamilies. Exon-intron structures were closely related to the phylogenetic relationship of the genes, and PYL genes that clustered in the same subfamily had a similar number of exons. VvPYL1, VvPYL2, VvPYL4, VvPYL7, and VvPYL8 were relatively highly expressed in roots. VvPYL1, VvPYL3, VvPYL7, and VvPYL8 were expressed in response to cold, salt, or polyethylene glycol stress. VvPYL6 was up-regulated by cold stress for 4 hours, and the expression of VvPYL2 was 1.74-fold greater than that of the control under cold stress. VvPYL8 was up-regulated 1.64-, 1.83-, and 1.90-fold compared with the control when treated with salt, PEG, or cold stress after 4 hours, respectively. Additionally, abiotic stress-inducible elements exist in VvPYL2, VvPYL3, VvPYL7, and VvPYL8, indicating that in these four genes, the response to abiotic stress may be regulated by cis-regulatory elements. The transcriptional levels of VvPYL1 and VvPYL8 significantly increased from fruit set to the ripening stage and decreased in the berry when treated by exogenous ABA. The eight VvPYL genes have diverse roles in grape stress responses, berry ripening, or development. This work provides insight into the role of VvPYL gene families in response to abiotic stress and berry ripening in grape.
Aneela Nijabat, Adam Bolton, Muhammad Mahmood-ur-Rehman, Adeel Ijaz Shah, Rameez Hussain, Naima Huma Naveed, Aamir Ali, and Philipp Simon
Heat waves occur with more regularity and they adversely affect the yield of cool season crops including carrot (Daucus carota L.). Heat stress influences various biochemical and physiological processes including cell membrane permeability. Ion leakage and increase in cell permeability are indicators of cell membrane stability and have been used to evaluate the stress tolerance response in numerous crops and inform plant breeders for improving heat tolerance. No study has been published about the effects of heat stress on cell membrane stability and relative cell injury of carrot. Therefore, the present study was designed to estimate these stress indicators in response to heat stress at the early and late seedling developmental stages of 215 diverse accessions of wild and cultivated carrot germplasm. The article identifies the relationship between early and late stages of seedling tolerance across carrot genotypes and identifies heat-tolerant genotypes for further genetic analysis. Significant genetic variation among these stress indicators was identified with cell membrane stability and relative cell injury ranging from 6.3% to 97.3% and 2.8% to 76.6% at the early seedling stage, respectively; whereas cell membrane stability and relative cell injury ranged from 2.0% to 94.0% and 2.5% to 78.5%, respectively, at the late seedling stage under heat stress. Broad-sense heritability ranged from 0.64 to 0.91 for traits of interest under study, which indicates a relatively strong contribution of genetic factors in phenotypic variation among accessions. Heat tolerance varied widely among both wild and cultivated accessions, but the incidence of tolerance was higher in cultivated carrots than in wild carrots. The cultivated carrot accessions PI 326009 (Uzbekistan), PI 451754 (Netherlands), L2450 (USA), and PI 502654 (Pakistan) were identified as the most heat-tolerant accessions with highest cell membrane stability. This is the first evaluation of cell membrane stability and relative cell injury in response to heat stress during carrot development.
Jin Wang, Yue Liu, Xueliang Chen, and Qiusheng Kong
Watermelon (Citrullus lanatus) is an economically important cucurbit (Cucurbitaceae) crop cultivated globally for its nutritional benefits. Fruit development in watermelon is characterized by fast fruit expansion attributed to unique biological processes. Myeloblastosis (MYB) family genes play important roles in plant growth and development, especially R2R3-MYB-type genes. However, the evolution of R2R3-MYB family genes in the watermelon genome and whether they participate in the regulation of watermelon fruit development remain unknown. To address these questions, duplication modes of R2R3-MYB family genes were identified and their expression profiles were investigated during watermelon fruit development. A total of 48 duplicated gene pairs were identified among the 89 R2R3-MYBs in watermelon. Segmental and transposed duplication events play major roles in the R2R3-MYB family gene expansion process. The ratio of nonsynonymous mutation and synonymous mutation analysis indicated that all the duplicated R2R3-MYBs experienced negative selection. Gene structures and cis-element compositions in promoter sequences exhibited abundant divergences between the R2R3-MYB duplicated genes. Transcriptome analyses of seed, rind, and flesh during fruit development showed that only two duplicated gene pairs had significantly similar expression patterns, whereas divergent expression profiles were found between the remaining duplicated gene pairs. Tissue-specific and development stage-specific divergent expression patterns demonstrated that neo-functionalization occurred between watermelon R2R3-MYB duplicated genes. The current study provides valuable information for further functional analyses of R2R3-MYBs in watermelon.
Kun Jia, Michelle DaCosta, and J. Scott Ebdon
Reseeding of creeping bentgrass (Agrostis stolonifera L.) under unfavorable temperature (≈10 °C) is a common practice on golf putting greens and fairways. Seed priming to enhance germination and early emergence increases seeding success. Seed priming comparing abscisic acid (ABA), gibberellic acid (GA), glycinebetaine (GB), hydrogen peroxide (H2O2), and polyethylene glycol (PEG) has not been investigated in turfgrass. Our objective was to compare these chemical primers at three concentrations with water- and unprimed-seed at two competing germinating temperatures (10 vs. 25 °C). Two seed lots of ‘T-1’ creeping bentgrass were compared. Curve fitting of daily germination was used to compute days to 50% germination (D50) and maximum germination percentage (Gmax). Cold (10 °C) significantly inhibited emergence (higher D50) more than Gmax. The effects of primers and their rates varied with the seed lot and temperature. Enhancement of seed germination measured as early emergence (lower D50) and/or higher Gmax were only detected at 10 °C. Osmotic primers (GB and PEG) were most effective in promoting germination relative to unprimed seed followed by hormone primers (ABA and GA) with redox primers (H2O2) least effective. Glycinebetaine primed seed was the only primer effective at all concentrations, with the 100 mм concentration the only concentration to enhance germination by increasing both Gmax and early emergence (lower D50) compared with unprimed seed.
Lushan Ghimire, Davie Kadyampakeni, and Tripti Vashisth
Huanglongbing [HLB (Candidatus Liberibacter asiaticus)] is one of the most devastating diseases in citrus (Citrus sp.). Field observations in Florida have shown that citrus groves with high soil and irrigation water pH decline rapidly under HLB-prevalent conditions. It is worth noting that irrigation water pH has always been high in Florida; however, neither tree decline nor low productivity under such conditions has been an issue for citrus before HLB. Therefore, there is a need to determine if HLB increases citrus tree sensitivity to high-pH irrigation water. The objective of this research was to evaluate the molecular and physiological responses of healthy and HLB-affected citrus trees irrigated with water at pH levels of 5.8, 7.0, and 8.0. The results demonstrated that soil pH is positively correlated with irrigation water pH. Overall, regardless of disease occurrence, tree performance decreased as pH increased. HLB-affected trees at pH 8.0 had the greatest mortality (40%) and leaf drop (87%) and the lowest height growth (<1%) and leaf biomass (0.1 g). In contrast, HLB-affected trees at pH 5.8 had the lowest mortality (0%) and leaf drop (16%) and the greatest height growth (6.6%) and leaf biomass (5.5 g). Growth and survival data indicate that high pH had a less negative impact on healthy trees than HLB-affected trees, and that HLB symptoms were exacerbated at pH 8.0 compared with pH 5.8. A transcriptomic analysis of root tissue conducted at the end of the experiment further suggested that HLB-affected trees at pH 5.8 were actively detoxing stress-induced radicals and had increased growth and developmental processes with the downregulation of jasmonic acid biosynthesis compared with healthy trees. This implies that at pH 5.8, HLB-affected trees were under less stress than healthy trees. Compared with healthy trees, HLB-affected trees at pH 8.0 resulted in upregulated immune system processes, defense responses, and cell death; no processes were significantly downregulated in HLB-affected trees compared with healthy trees at pH 8.0. Physiological and molecular observations suggest an interaction between HLB and irrigation water pH whereby HLB symptoms are exacerbated in response to high irrigation water pH.
Toshio Shibuya, Ryosuke Endo, Yoshiaki Kitaya, and Mizuki Tsuchida
The light competition in dense plant stands may be disadvantageous in transplant production because competition stimulates stem elongation and can reduce photosynthate allocation to leaves; this, in turn, may reduce the early growth rate after transplanting. In this study, we focused on how the proportion of far-red (FR) light affected light competition among cucumber (Cucumis sativus L.) seedlings and investigated the effects of the plant density × FR interaction on photosynthate allocation and subsequent early growth after transplanting. Seedlings at the cotyledon stage were planted into plug trays at densities ranging from 109 to 1736 plants/m2; then they were grown for 4 days under light-emitting diode (LED) light containing FR light (FR+) at approximately the same red-to-FR ratio as in sunlight (1.2) or under light containing no FR (FR−). The higher density significantly stimulated stem elongation under both FR+ and FR−, but the effect was small under FR−; this indicates that light competition in the dense stands was inhibited by reducing FR light. The higher plant density significantly increased photosynthate allocation to the stem and decreased allocation to the leaves under both FR+ and FR−; however, again, the effect was smaller under FR−. After transplanting the seedlings to pots, early growth decreased in the seedlings that allocated less photosynthate to their leaves. Our results indicate that light with reduced FR can mitigate the disadvantageous photosynthate allocation of transplants and the reduction of early growth after transplanting that are likely to occur as a result of light competition at high plant density.
Young consumers value healthy foods and are willing to pay for them. As young consumers transition into higher paying jobs, their influence in the food system will compound. This study used a convenient sample of university students to understand how young consumers value attributes for fresh produce. With the proliferation of food labels, this study takes a step back to identify four consumer segments with regard to their values on explicit (i.e., organic and local) and implicit (i.e., small-family farms and sustainable) attributes: committed, farm-to-fork, unattached, and skeptic. The study also investigated the impact of personal motives on cluster membership. Although committed consumers placed high value on all attributes, farm-to-fork consumers valued local, sustainable, and small-family farm systems, but did not have positive valuation toward organic. Our findings suggest increasing access to local foods and farmers market patronage is likely to increase consumers’ valuing foods with local, organic, sustainable, and small-family farms attributes.