Copper (Cu) is an essential micronutrient for plants and is the a.i. in pesticides for some pathogens and algae. Elevated doses of Cu can cause toxicity in plants. While silicon (Si) is reported to alleviate the toxicity of some heavy metals, its role in reducing the symptoms induced by excess Cu is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in arabidopsis [Arabidopsis thaliana (L.) Heyn.]. Based on plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of phenylalanine ammonia lyase [PAL (EC 184.108.40.206), a stress-induced enzyme] activity in the shoot, Si was found to alleviate copper stress. Real-time reverse transcriptase-polymerase chain reaction analyses indicated that the RNA levels of two arabidopsis copper transporter genes, copper transporter 1 (COPT1) and heavy metal ATPase subunit 5 (HMA5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of arabidopsis to Cu stress, and this improvement operates on multiple levels, ranging from physiological changes to alterations of gene expression.
Jie Li, Scott M. Leisner, and Jonathan Frantz
Jenny Heringer Vires, Robert Anderson, and Robert Geneve
Purple Coneflower [Echinacea sp. (Asteracea)] is of great value to the horticultural, pharmaceutical, and herbal industry. More research is needed to determine cultural practices that will produce a plant high in biomass and phenolic content, the chemical used for testing the quality of the harvested plant on a percent basis of roots, flowers and vegetative parts. The objective of this experiment is to determine if biomass and phenolic content of Echinacea purpurea and E. purpurea `Magnus' is influenced by fertilization after flower bud removal and vegetative pruning. The second objective of this study is to form an evaluation of the differences in biomass and phenolic content of five cultivars of E. purpurea and five species of Echinacea. Biomass and phenolic content will be evaluated to determine if exposing these plants to various treatments increases the quality of the plant over 1 and 2 years of growth. Differences in dry weights of Echinacea species and cultivars harvested after the first year of growth was determined. There was a significant difference in total dry weight between E. purpurea cultivars. Echinacea purpurea `Bright Star' and `Clio' significantly produced the most total dry weight compared to all other cultivars. There was no significant difference in root or flower biomass between cultivars. Biomass of Echinacea species was significantly different in root, vegetaive and flower parts. The total biomass of E. purpurea and E. tennesseensis was significantly higher compared to other species. Echinacea pallida and E. paradoxa were not significantly different from E. purpurea in root biomass, even though both species were small in above ground growth. Echinacea tennesseensis significantly produced 45% to 105% more flowers compared to other species. Differences in phenolic content between species and cultivars will also be presented.
Gisele G. Martins, Robert Geneve, and Sharon Kester
Quercus falcata acorns were cold-stratified for 120 days and then sown in vermiculite under greenhouse conditions. When radicles were 7 cm long, the root tip was either removed (physically pruned) or dipped in a copper hydroxide solution (copper-treated). Intact root systems were used as control. Seedlings were then moved to a root box to observe root system architectures. The box was built of clear plexiglass 2.5 mm thick, and each face was 25.7 × 35.7 cm. Styrofoam spacers were used to separate faces, and nuts and bolts were placed along edges to hold the root box together. To permit observation of the entire root system, plants were grown in a plane between the plexiglass surface and a nylon sheet that separated roots from the medium (MetroMix 510). At 7, 9, and 11 days after treatment, the entire root system was traced on an acetate sheet, and number of internal and external links and number of secondary and tertiary roots were recorded. Total length, internal and external root links length, were obtained using digital analysis (MacRhizo). Dry weight of roots and shoots was collected at the end of this experiment (day 11). Treatment effects were evident 11 days after treatment. Copper-treated plants had statistically more secondary roots and larger internal link length than control or physically pruned plants. Also, copper-treated plants had smaller mean external link length, showing a more branched root system. Root biomass was similar for all treatments; however, copper-treated plants had smaller root: shoot ratio. This suggests that copper was acting as more than a pruning agent because copper-treated plants showed a different root system architecture compared to physically pruned plants.
Marcelino Bazán-Tene, Jaime Molina-Ochoa, and Enrique Alejandro Bracamontes-Ursúa
Hot pepper (HP), Capsicum annuum (L.), is a solanum plant domesticated in Mesoamerica. It is currently widespread worldwide, and its uses are varied, such as an excellent flavoring, pigment base, and as a food resource with source of vitamins. The seven top world producers of HP are China, Mexico, Turkey, Spain, United States, Nigeria, and Indonesia. Mexico is producing about 623,238 t/year of fresh fruits in 136,398 ha; Colima produced 17,181 t in 676 ha, with a mean of 27 t·ha-1. The culture of HP in Colima is facing certain limitations in showing its productive potential, such as maintaining fertile and well-drained soils, and constant soil moisture; being weed-free during the first weeks after transplanting; and sustaining plant uniformity into transplantation. Transplantation is made in seed beds, but there is a lack of scientific evidence on shade requirements in the seed nursery to accelerate and improve plant quality for transplanting, and to impact on fruit yield. The aim was to evaluate the effect of levels of shading on the germination and vegetative development of `Serrano' HP under greenhouse conditions. Four levels of shading were evaluated using mesh fabrics to produce 90%, 75%, and 50% shade, and a control without shading on the seed beds. A completely randomized design with four treatments and four replications was used. The shading treatments reduced the germination period in about 1 day, increased the percentage of germination with a range between 1.75% and 3.25%; increased the plant height 0.83, 2.85, and 4.38 cm at 3, 6, and 10 days post-emergence; increased the root biomass about 0.01 g/plant, and 0.24 g of fresh foliage with the 90% shade compared with the control. Overall, a better agronomic performance of `Serrano' HP was obtained with 90% shading.
Mario Orozco-Santos, Javier Farías-Larios, Jaime Molina-Ochoa, and José Gerardo López-Aguirre
Development of resistance to chemical pesticides has been reported in about 150 plant pathogenic species, mostly fungi. Biocontrol of plant pathogens is an alternative to chemical pesticides. Actually, there are products formulated with beneficial microorganisms, such as mycorrhizal fungi, rhizobacteria, antagonistic fungi, and others. The objective was to evaluate the development of Fusarium oxysporum f. sp. melonis (FOM) on melon plants inoculated with commercial biological formulations based on beneficial microorganisms. Twelve treatments were evaluated: T1) VAM media nursery + FOM; T2) Hortic Plus + FOM; T3) BioPak F + FOM; T4) Glomus intraradices + FOM; T5) FOM; T6) control; T7) VAM media nursery; T8) Hortic Plus; T9) BioPak F; T10) Glomus intraradices; T11) FOM + Mancozeb wp80; and T12) FOM + BioPak F. The melon cultivar used was `Colima' (Peto Seed Co.). Seeds were planted in Styrofoam growing containers containing coconut fiber powder as substrate. One seed was planted per cell and maintained until transplanting. Plants were transplanted to pots containing sterile soils 13 days postemergence. Inoculation of treatments with Fusarium was made with a concentrated suspension at 1 × 106 conidia/mL. For inoculation with beneficial microorganisms, manufacturer specifications were followed. A completely randomized design with 12 treatments and 12 replications was used to estimate the incidence of Fusarium, number of leaves, leaf area, root biomass, and percentage of roots colonized by mycorrhizal fungi. Overall, T10 showed the best behavior in all variables. Inoculation of cantaloupe plants with Fusarium affected their performance, but those treatments including mycorrhizal fungi enhanced their performance withstanding the damage by Fusarium.
Marcelino Bazan Tene, Juan Manuel González Gonzalez, Francisco Radillo Juarez, Jorge Pahul Covarrubias Corner, and Salvador Guzman Gonzalez
The hot pepper (Capsicum annuum L.) is a plant domesticated in Mesoamerica. Hot pepper is currently widespread worldwide, and its uses are varied, such as for flavoring, pigment base, and as a nutritional food resource. Mexico produces about 623,238 tons/year of fresh fruits in 136,398 ha; the State of Colima produced 17,181 tons in 676 ha, with a mean of 27 t·ha-1. The culture of hot pepper in Colima faces certain limitations to its productive potential, such as lack of fertile and well-drained soils, constant soil moisture, and being free of weeds during the first weeks after transplanting; and maintaining plant uniformity in transplantation. This last practice is carried out in the side bed, but there is a lack of scientific evidence about the requirements of luminosity in the seed nursery in order to accelerate improvement of plant quality for transplanting, and the impact on fruit yield. The aim of this study was to evaluate the effect of different levels of shading on germination and vegetative development of `Jalapeño' hot pepper under greenhouse conditions. Four levels of luminosity were evaluated using mesh fabrics in order to produce 90%, 75%, and 50% shade, and control (0%) without shading on the seed beds. A completely randomized design with four treatments and four replications was used. The shading treatments reduced the germination period in about 2 days; increased the percentage of germination with a range between 1.6% and 3.7%; increased the plant height 2.3, 4.8, 7.72, and 10.1 cm at 3, 7, 13, and 18 days postemergence; increased the root biomass about 7.1 g/plant, and 5.4 g of fresh foliage with the 90% shade treatment in comparison with control. Overall, a better agronomic performance of the `Jalapeño' hot pepper was obtained with 90% shading.
Mindy L. Bumgarner, K. Francis Salifu, Michael V. Mickelbart, and Douglass F. Jacobs
Excessive fertilization may induce physiological drought and/or ion toxicity, which can reduce growth or cause mortality in cultured plants. Although nursery subirrigation produces stock of forest trees of equal or better quality to conventional overhead irrigation, detailed analyses of fertilization responses specific to these systems are lacking. We evaluated the effects of fertility applied as a 15N–9P–12K controlled-release fertilizer at rates equivalent to 0, 1.2, 1.8, 2.4, 3.0, or 3.6 g nitrogen (N) per plant on media properties and northern red oak (Quercus rubra L.) seedling development grown with subirrigation. Aboveground plant growth and nutrient content of seedlings increased up to 1.8 g N/plant but declined at higher rates and total mortality occurred for treatments of 2.4 to 3.6 g N/plant by the end of cultivation. Root biomass generally declined with increasing fertilization. Media electrical conductivity (EC) increased with increasing fertility, particularly in the upper media layers, where values exceeded 3.0 dS·m−1 at the highest rates. Fertilization had little effect on media pH. Predawn leaf water potential and osmotic potential (ψS) were reduced at high nutrient applications. Thus, increasing fertility beyond ≈1.8 g N/plant in this subirrigation system apparently resulted in accumulation of excessive fertilizer salts in media and/or ion toxicity, which caused plant mortality. Because subirrigation systems are prone to persistence of residual fertilizer salts in the medium and holding tanks, fertilization prescriptions must be carefully tailored to species and cultural systems to prevent potential for plant damage associated with overfertilization.
Christian M. Baldwin, Haibo Liu, Lambert B. McCarty, William L. Bauerle, and Joe E. Toler
Studies on bermudagrasses (Cynodon spp.) have demonstrated variability in salinity response among species and cultivars. However, information on ultradwarf bermudagrass cultivars in relative salinity tolerance associated with trinexapac-ethyl (TE) [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxocyclohexanecarboxylic acid ethyl ester], a cyclohexanedione type II plant growth regulator (PGR), remains unknown. Therefore, two replicated greenhouse studies were conducted to determine the salinity tolerance of two ultradwarf bermudagrass cultivars treated with TE on turfgrass quality (TQ), total root biomass, and root and shoot tissue nutrient concentration. Turfgrasses included `TifEagle' and `Champion' bermudagrass (Cynodondactylon(L.) Pers. × C. transvaalensisBurtt-Davy). Daily sodium chloride (NaCl) exposure was 0, 12.90 (8,000 ppm), 25.80 (16,000 ppm), and 38.71 dS·m–1 (24,000 ppm). Biweekly TE applications (active ingredient 0.02 kg·ha–1) were initiated 2 weeks after salinity exposure. `Champion' was more salt-tolerant than `TifEagle' based on TQ and root mass. At 12.90, 25.80, and 38.71 dS·m–1 of NaCl, nontreated (without TE) `Champion' consistently outperformed nontreated `TifEagle' with greater TQ on most rating dates. At 12.90 dS·m–1, TE treated `Champion' (8.0) had greater TQ than nontreated `TifEagle' (6.1) at week 10. Regardless of TE application, after 2 weeks of applying 25.80 dS·m–1 of NaCl, both cultivars fell below acceptable TQ (<7). When averaged across all salinity treatments, applying TE four times at 0.02 kg·a.i./ha in two week intervals enhanced root growth for both bermudagrass cultivars by 25%. Also, both cultivars decreased root mass as salinity levels increased. Non TE-treated `TifEagle' had 56% and 40% less root and shoot Na uptake compared to TE treated cultivars at 25.80 dS·m–1. In conclusion, the two bermudagrass cultivars responded differently when exposed to moderate levels of NaCl.
Olive plants for commercial production are vegetatively propagated by cutting and grafting. While genetic identity can be maintained by “own root”; plants by cutting, the grafted plants may show different growth characteristics due to the influence of the rootstock. The selection of mother plants, able to produce seeds with desirable characteristics and rootstocks that may control seedling growth in grafted stock, can be an objective of study to facilitate the development of olive breeding programmes. The relationship between seed biomass, mineral nutrient reserves, time to germination and seedling growth was analysed for six cultivars of Olea europaea. The cultivars, exhibiting initial differences in seed biomass, differed significantly with respect to germination capacity, germination time and mineral content. Significant variation among cultivars was also evident in the linear growth of seedlings, evaluated at different intervals from 2 to 30 weeks. The seeds from all six cultivars exhibited low germination. There is a significant effect of cultivar on the levels of single mineral nutrient content of seeds, high concentrations of N and significant concentrations of K, P, Mg, and Ca were detected. Seed biomass was not related to time to germination and the levels of single nutrients of the seeds themselves. For seed tissue, significantly positive correlations existed only between K, and Mg concentrations. Seed biomass was positively and significantly related to root biomass. The seedlings obtained from larger seeds showed a substantially greater proportion of biomass to roots. Some root traits may be important for survival and the establishment of the seedlings, not least under conditions of limited water availability.
J.T.A. Proctor, T. Slimmon, and P.K. Saxena
Ginseng is an herbaceous perennial that grows in the understorey of deciduous hardwood forests and is also cultivated for its highly valued root. The primary method of propagation of ginseng is by seed which requires the breaking of dormancy by stratification, a process which takes 18–24 months. Investigation of factors controlling the growth and development of ginseng plants is a prerequisite to the development of a more efficient system of ginseng propagation. We have recently modulated the morphogenetic potential of geranium roots and stimulated de novo development of shoots and embryo-like structures which later formed whole plants using thidiazuron (TDZ). Our objective was to investigate the morphological changes in seedling and mature ginseng plants induced by TDZ, particularly in relation to root and shoot morphogenesis and economic yield. Applications of TDZ (0.22 and 2.20 ppm), either as foliar sprays or soil watering to greenhouse-grown seedlings over 18 weeks (2 weeks after sowing to 20 weeks when plants were harvested) induced similar effects. These responses included increased stem length and diameter, and shoot and root weight (economic yield). Single foliar applications of TDZ at 62.5 and 125 ppm to 3-year-old field-grown ginseng plants 3 months before harvest increased root biomass (economic yield) by 19% to 23%. Roots of TDZ-treated seedlings and 3-year-old field-grown plants developed thickened secondary roots on the upper part of the taproot. The root-like structure of these secondary roots was confirmed by histology. In addition, TDZ treatments induced adventitious buds on the shoulder of 3-year-old roots. These buds developed into shoots to give multi-stem plants following a period of dormancy, which was overcome with GA3 (gibberellic acid) treatment before planting.