Alexandre Furtado Silveira Mello, Giovani Olegário da Silva, Juscimar da Silva, Tarcísio Samborski, José Carlos Ferreira, José Luiz Viana de Carvalho, Marília Regini Nuti, Ana Carolina Silva Siquieroli, Marcos Brandão Braga, Federico Celedonio Diaz Trujilo, and Wolfgang Grüneberg
Hamidou F. Sakhanokho, Nurul Islam-Faridi, and Barbara J. Smith
Ziziphus mauritiana Lam. is a widespread shrub or tree of the Sahel region, where it grows wild and is used for various purposes, including nutrition, medicine, and firewood. Current domestication programs focus on using the local species as rootstock for the improved imported Asian cultivars to provide tolerance to pests and diseases. The plant plays an increasing economic role in the livelihoods of local Sahelian populations, but despite this there is little genetic information about it. The purpose of our study was to determine the genome size estimate and chromosome numbers of Z. mauritiana germplasm collected from eastern Senegal, West Africa. Genome size estimates were determined using flow cytometry, and chromosome count was achieved using chromosome spreads of actively growing root tips. The mean, median, minimum, and maximum genome size estimates (1Cx-DNA) of Z. mauritiana were 418.74 Mb, 417.45 Mb, 410.72 Mb, and 432.12 Mb, respectively. Plants of the germplasm investigated were found to be octoploid with a chromosome number of 2n = 8x = 96. The genetic information gathered in this study can be useful for phylogenetic studies, sequencing projects, and domestication programs that focus on controlled pollination for the development of improved Z. Mauritania cultivars in the Sahel region.
Sukhdeep Singh, Taylor Livingston, Lisa Tang, and Tripti Vashisth
Fruit production of sweet orange (Citrus sinensis) in Florida has been declining with the presence of Huanglongbing [HLB; Candidatus Liberibacter asiaticus (CLas)] disease. Through disruption of the balance of endogenous hormone levels, the disease has negative impacts on fruit development, mature fruit retention, and overall tree health. Thus, the goal of this research was to determine whether plant growth regulator gibberellic acid (GA3) can be used to improve the production issues caused by HLB. For ‘Valencia’ sweet orange, although foliar applied GA3 from September to January (33 mg·L−1 for five applications) resulted in 50% decrease in bloom the following spring (results presented in ), this treatment did not cause reduction in yield of current and subsequent crops. Moreover, a 30% average increase in yield in GA3-treated trees was observed over a period of 4 years. The size of mature fruit was also increased (by 4% to 5%) with reduced fruit drop rate near harvest in GA3-treated trees compared with nontreated control trees. Furthermore, the canopy density, an indicator of HLB severity, was maintained in trees applied with GA3 (from 90.8% light interception to 90.4%). In contrast, there was a substantial decrease in canopy density for control trees (from 91.6% to 84.0%). Gene expression analysis of abscission zone and leaves indicated that GA3-treated trees had enhanced oxidative stress mitigation mechanism and plant defense response. Given that there is no cure for HLB, these results presented a possible remedy of using GA3 in sustaining tree health for field-grown sweet orange affected by HLB.
Thomas E. Marler
Conservation of the endangered Serianthes nelsonii is constrained by lack of research. Transplanted containerized plants die in the competitive in situ environment. This study determined if foliar applications of nutrient solution could replace edaphic fertilizer applications for mitigating competition for soil nutrients. Weekly sprays with 0.1× Hoagland solution were compared with weekly drenches of 0.5× Hoagland solution. Plants receiving edaphic or foliar nutrition were not different in height, and height growth was 72% above that of control plants. Similar results were obtained for stem diameter and leaf number. Leaf nutrient concentrations were not different for the two nutrition treatments, but stem nutrient concentration differences were dependent on the element. Stem copper, nitrogen, phosphorus, potassium, and zinc concentrations were not different for edaphic vs. foliar nutrition. Contrarily, stem boron, calcium, iron, magnesium, and manganese concentrations were greater in plants receiving edaphic nutrients. The results indicate nutritional needs of recently out-planted plants may be supplied directly to leaves to mitigate below-ground competition for nutrient resources.
Steven C. Haring, Junjun Ou, Kassim Al-Khatib, and Bradley D. Hanson
Grape growers are concerned about the potential impact of drift from commonly used auxinic herbicides. In California, this is frequently related to herbicides used in cereals and noncrop areas, whereas in other parts of the United States concerns are often related to dicamba- and 2,4-D-resistant cropping systems. Our objective was to compare the relative sensitivity of winegrapes to simulated auxinic herbicide drift, including grapevine symptomology, grape yield, and grape quality. In a small-plot herbicide evaluation, we applied 1/900×, 1/300×, 1/100×, and 1/33× rates of 2,4-D, aminopyralid, dicamba, and triclopyr based on 1× field rates of 1454, 122.5, 280, and 2240 g⋅ha–1 ae, respectively. Aminopyralid resulted in similar symptomology to 2,4-D and dicamba—namely, leaf cupping, leaf crinkling, excessive tendril twisting, and tendril death, although these symptoms were generally subtle. Triclopyr resulted in much greater levels of necrosis compared with the other herbicides. In our study, triclopyr was the only herbicide associated with grape yield loss, and greater triclopyr rates were also associated with increased grape sugar levels. This study demonstrates that grapes are sensitive to low rates of simulated herbicide drift, but symptoms do not necessarily indicate yield loss or quality effects. This study indicates that auxin-type herbicide simulated drift symptoms are not reliable markers for winegrape yield or quality reduction.
Wenqian Zhang, Xiaoling Jin, Donglin Zhang, Minhuan Zhang, and Wen Xing
Paul C. Bartley III, Aziz Amoozegar, William C. Fonteno, and Brian E. Jackson
The heterogeneity of horticultural substrates makes basic physical characteristics, such as total porosity and particle density, difficult to estimate. Due to the material source, inclusion of occluded pores, and hydrophobicity, particle density values reported from using liquid pyknometry, vary widely. Gas pycnometry was used to determine the particle density of coir, peat, perlite, pine bark, and wood substrates. Further precision was examined by gas species and separation by particle size. The calculated particle densities for each material determined by He, N2, and air were relatively constant and varied little despite the species of gas used. Particle size affected the measured particle density of perlite and pine bark but was minimal with coir, peat, and wood. Reducing the particle size removed more occluded pores and the measured particle density increased. Given the small variability, the use of particle density values obtained by gas pycnometry provides repeatable, precise measurements of substrate material total porosity.