Search Results

You are looking at 31 - 40 of 169 items for :

  • impermeability x
  • Refine by Access: All x
Clear All
Free access

Yung-I Lee, Nean Lee, Edward C. Yeung, and Mei-Chu Chung

This investigation documents the key anatomical features in embryo development of Cypripedium formosanum Hayata, in association with the ability of embryos to germinate in vitro, and examines the effects of culture media and seed pretreatments on seed germination. A better understanding of zygotic embryogenesis for the Cypripedium L. species would provide insights into subsequent germination events and aid in the in vitro propagation of these endangered species. In seeds collected at 60 days after pollination (DAP), soon after fertilization, no germination was recorded. The best overall germination was found at 90 DAP (≈70%), at which time early globular to globular embryos with a single-celled suspensors can be observed. After 135 DAP, the seeds germinated poorly. At this time the inner integument shrinks and forms a tight layer, which encloses the embryo, the so-called “carapace.” Using Nile red stain, a cuticular substance was detected in the carapace, which may play a role in the impermeability of the mature seed and may help the seeds survive in the stringent environment. At maturity (after 210 DAP), the embryo proper has an average size of eight cells along its length and six cells across the width. Lipids and proteins are the main storage products within the embryo. To improve seed germination, experiments were conducted to test the suitability of various media and pretreatments of seeds. When different media were used, except for the Harvais medium at 120 DAP, there was no significant difference in seed germination at three different developmental stages tested. Soaking mature seeds in 1% NaOCl or treating them with ultrasound may slightly increase the germination percentage. For seed germination, our results indicate that the timing of seed collection outweighs the composition of medium and the seed pretreatments.

Free access

S.D. Nelson, C. Riegel, L.H. Allen Jr., D.W. Dickson, J. Gan, S.J. Locascio, and D.J. Mitchell

One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cis- or trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film - VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin).

Open access

Bijan Dehgan and Bart Schutzman

Abstract

Germination of Cycas revoluta seed is slow and erratic when planted immediately after collection, and most lose viability in a few months. In a 2 × 4 × 4 factorial experiment, seeds were stored at 5° and 22°C for 24 weeks and subsequently treated with H2SO4 (18 M) for 0, 1, 2, or 3 hr followed by GA3 (1000 ppm) for 0, 24, 48, or 72 hr. Morphophysiological complex dormancy contributes to the lengthy germination process. Removal of the fleshy, water-repellant sarcotesta (containing inhibitors), scarification of the thick water-impermeable sclerotesta, and maturation of the embryo, which is in very early stages of development at the time of seed abscission, all enhance germination. At 5°, 92% of the seeds survived, but only 42% of the seeds stored at 22° were viable after 24 weeks, the result of desiccation. Under all but 72 hr of GA3 exposure time, response surface shapes lead to the expectation that germination will be better without H2SO4 or with higher levels of H2SO4 than with intermediate levels. The response to GA3 at any given exposure to H2SO4 is similar in both cold- and warm-stored seeds: for a given GA, level, one optimum H2SO4 exposure gives the best germination percentage, peak value (PV), or germination value (GV). Optimal GV results when seeds are stored at 5° for 24 weeks to allow embryo maturation followed by removal of the sarcotesta, 1 hr of H2SO4 exposure, and 36 hr of GA3 exposure.

Open access

W. J. Davies and T. T. Kozlowski

Abstract

Each of 8 antitranspirants reduced transpiration of 2 species of woody plants. Dow Silicone and CS 6432 were the most effective compounds on Fraxinus americana and Dow Silicone was effective on Pinus resinosa. Keykote, Folicote and Improved Wilt Pruf showed an increased effect on plant water loss and net photosynthesis (measured by net CO2 uptake) of P. resinosa up to 8 days after compound application. Thereafter there was no significant change in the effect of any compound on transpiration or photosynthesis. Effects on F. americana of all compounds except Improved Wilt Pruf decreased with time after application. Scanning electron micrographs of treated leaves suggested that antitranspirant films on F. americana leaves cracked over the guard cell pore, accounting for the decrease in compound effect with time. Antitranspirants apparently reduced water loss of P. resinosa by combining with wax in the stomatal pore and forming an impermeable plug. The compounds tested were toxic to F. americana seedlings and photosynthesis of treated plants decreased with time, even when direct physical effect of a compound had worn off. Pinus resinosa seedlings showed no decrease in photosynthesis with time. F. americana plants treated with Keykote exhibited low rates of water loss and transpiration/photosynthesis ratios that were not significantly different from those of control plants. Folicote was toxic, and Clear Spray increased water loss of F. americana seedlings. Dow Silicone reduced water loss of Pinus seedlings by about 80%, and plants treated with Dow Silicone, Improved Wilt Pruf, Keykote, or Folicote had favorable transpiration/photosynthesis ratios. The effects of antitranspirants on transpiration and photosynthesis were greatly influenced by environmental regimes and by species.

Free access

Johan Desaeger and Alex Csinos

The effects of drip-applied 1,3-dichloropropene (1,3-D) and chloropicrin on fumigant soil gas levels and growth of vegetable seedlings were investigated in three separate tests in Tifton, Ga. Tests were conducted in Spring 2002, Fall 2002, and Spring 2003. Phytotoxicity of 1,3-D + chloropicrin was induced in the 2002 tests by applying progressively higher rates (0 to 374 L·ha–1) of drip-irrigated InLine (an emulsifiable formulation (EC) containing 60.8% 1,3-D and 33.3% chloropicrin) and planting vegetable seedlings within four days after application. Vegetables evaluated were tomato, pepper and cucumber (Spring 2002), and tomato and squash (Fall 2002). In Spring 2003, the effects of 1,3-D formulation (InLine versus Telone EC, an EC containing 94% 1,3-D), plastic mulch type [low density polyethylene (LDPE) versus virtually impermeable film (VIF)] and drip tape configuration (one versus two drip tapes) on fumigant soil gas levels and growth of tomato were investigated. Tomato was planted after the recommended 3-week waiting period. Fumigant concentrations in soil were measured using Gastec detection tubes at 1 to 4 days after drip fumigation in all three tests. Measured fumigant soil gas concentrations were correlated with fumigant application rates in Spring 2002, but not in Fall 2002. Vegetables were visibly affected by residual fumigant levels in the soil and showed symptoms such as leaf chlorosis (cucumber, squash and pepper), leaf bronzing (tomato) and stem browning and stunting (all crops). Fumigant soil air levels were negatively and linearly correlated with different plant growth parameters, in particular plant vigor. The cucurbit crops showed an immediate response and high mortality within 1 week after planting. Surviving plants recovered well in fall. The solanaceous crops showed a more delayed response and lower mortality rates. However, phytotoxic effects with tomato and pepper were more persistent and plants did not seem to recover with time. Overall, fumigant residue levels and potential phytotoxicity were greater in spring than in fall. Greater fumigant soil concentrations were measured under VIF as compared to LDPE plastic mulch. The effect of drip-tape configuration varied with the type of plastic mulch that was used. The double-tape treatment resulted in lower fumigant levels at the bed center under LDPE mulch, and higher fumigant levels at the bed shoulder under VIF mulch. The formulation containing 94% 1,3-D resulted in higher soil fumigant levels as compared to the formulation containing 61% 1,3-D and 33% chloropicrin, especially with VIF mulch. Early plant vigor of tomato was negatively correlated with fumigant soil gas levels, and was especially poor following drip fumigation with 94% 1,3-D under VIF mulch.

Free access

James P. Gilreath, Bielinski M. Santos, Myriam N. Siham, Paul Vaculin, and Michael Herrington

Previous research has demonstrated stimulation of purple and yellow nutsedge (Cyperus rotundus and C. esculentus) with chloropicrin when applied at rates ranging from 100 to 150 lbs/acre (112 to 168 kg·ha–1) under low or high density polyethylene film mulch. This stimulatory effect has been exploited in research by developing a program of metam application 5 days after application of chloropicrin, thus placing metam in the soil once the tubers have begun to sprout and are most vulnerable. This project was expanded in 2004–05 to include the commercial emulsifiable concentrate formulation of 65% 1,3-dichloropropene and 35% chloropicrin (1,3-D + Pic) and virtually impermeable film mulch as well as high density polyethylene film. The test site was a commercial tomato farm in west central Florida with a heavy infestation of purple nutsedge. Chloropicrin was applied into raised beds through three gas knives, while 1,3-D + Pic and metam potassium were applied in 1 acre inch of water through 2 drip irrigation tubes spaced 10 inches apart and 5 inches from the bed center. Metam was applied 5 days after application of chloropicrin and 1,3-D + Pic. Treatments were applied under both standard high density polyethylene film (Hilex and Bromostop) VIF. Stimulation of nutsedge sprouting and emergence was about the same with either chloropicrin alone or combined with 1,3-D; however, there was some enhancement when applied under VIF. There was a slight improvement in efficacy of metam potassium when applied alone under VIF, contrary to previous results. Application of metam 5 days after application of chloropicrin or 1,3-D + Pic greatly improved nutsedge control over that observed without the subsequent application of metam and VIF improved results to some degree. Producers of drip irrigated crops in Florida can achieve acceptable to excellent nutsedge control using this sequential application technique combined with VIF; however, the addition of a second drip tube on the bed top increases expense by about $125/acre and is not compatible with crops grown with more than a single row on the bed.

Free access

Borut Gosar and Dea Baričevič

RFRRH system with mulches manages plant cultivation even under impermeable mulch without using an irrigation system, which was novel in plant production systems. The results of this 1-year study ( Gosar et al., 2010 ) showed that the RFRRH system did not

Full access

Carlene A. Chase, William M. Stall, Eric H. Simonne, Robert C. Hochmuth, Michael D. Dukes, and Anthony W. Weiss

An evaluation of the effect of bed width (24, 28, 32, and 36 inches) on the control of a mixed population of nutsedge [yellow nutsedge (Cyperus esculentus) and purple nutsedge (C. rotundus)] was conducted with an emulsifiable concentrate formulation of a 1,3-dichloropropene (1,3-D) and chloropicrin (CP) mixture (1,3-DCP) for application through drip irrigation systems. Beds were mulched with either 1.4-mil-thick virtually impermeable film (VIF) or 0.75-mil-thick high-density polyethylene (HDPE) and 1,3-DCP was applied at 35 gal/acre by surface chemigation or via subsurface chemigation 6 inches deep within the bed. HDPE was more permeable to gaseous 1,3-D than VIF so that 1 day after treatment (DAT), 1,3-D gas concentration at the bed centers under VIF was significantly higher than under HDPE. Dissipation of 1,3-D gas with HDPE occurred within 7 DAT, but dissipation with VIF took ∼10 days. In bed centers, 1,3-D concentrations 1 DAT were in the range of 2.3 to 2.9 mg·L–1 whereas in bed shoulders concentrations ranged from 0.1 to 0.55 mg·L–1. In 2002 and 2003, 1,3-D concentration in shoulders of narrower beds was significantly higher than in the wider beds, but dissipated more rapidly than in wider beds. Lower initial 1,3-D concentrations were observed with HDPE film in shoulders than with VIF and the rate of dissipation was lower with VIF. At 14 DAT, nutsedge plants were densely distributed along bed shoulders (19 to 27 plants/m2) with little or no emergence in the centers of beds (fewer than 5 plants/m2), but with no response to bed width. Nutsedge density increased with time, but the nature of the increase differed with bed width. The most effective nutsedge suppression was achieved with 36-inch beds, which had densities of 11–13 plants/m2 on bed centers and 53 plants/m2 on bed shoulders by 90 DAT. Nutsedge suppression was initially more effective with VIF than with HDPE film, so that no nutsedge emerged in the centers of beds mulched with VIF compared with 2–7 plants/ m2 with HDPE by 14 DAT. On bed shoulders there were 2–7 plants/m2 with VIF and 32–57 plants/m2 with HDPE. Increase in nutsedge density with time was greater with VIF so that by 90 DAT nutsedge densities on bed centers and shoulders were greater than with HDPE in 2002 and the same as with HDPE in 2003. Subsurface chemigation did not consistently improve suppression of nutsedge when compared with surface chemigation. Concentrations of 1,3-D in bed shoulders irrespective of bed width were nonlethal. Initial superior nutsedge suppression with VIF did not persist. Nutsedge control in a sandy soil with 1,3-DCP chemigation is unsatisfactory with one drip-tape per bed.

Free access

Howard F. Harrison Jr., D. Michael Jackson, Judy A. Thies, Richard L. Fery, and J. Powell Smith

produce seeds with impermeable seedcoats (hard seeds). The major attributes of lines US-1136, US-1137, and US-1138 have rapid growth, high biomass production, a long vegetative growth period, and southern root knot nematode [ Meloidogyne incognita

Open access

Emily Merewitz

. Ice layers can form in different ways, leading to either a porous or nonporous ice, which causes them to be permeable or impermeable to gases, respectively. Permeable or porous ice is typically not as detrimental to turf health when compared with