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Sandra R. Menasha* and Milton E. Tignor

Sweet corn (Zea mays L.) is difficult to transplant due to poor root regeneration. Despite reduced yields, growers are transplanting sweet corn to hasten maturity time to target profitable early markets in the Northeast. Researchers have ascribed the negative impacts on yield to restricted rooting volume. Therefore, the impacts plug cell volume had on sweet corn transplant root architecture and biomass accumulation were investigated. `Temptation' sweet corn was sown in volumes of 15, 19, 14, and 29 mL correlating to transplant plug trays with plug counts of 200, 162, 128, and 72 plugs per tray. Plug cells were exposed to three substrate environments; a dairy manure based organic compost media, a commercial soil-less germination mix, and the soil-less media supplemented 2X with 200 ppm soluble 3-3-3 organic fertilizer. A 4 × 3 factorial randomized complete-block experimental design with two blocks and five replicates per treatment was repeated twice in the greenhouse. For each experiment a total of three center cells were harvested from each replicate for analysis using the WinRhizo Pro root scanning system (Regent Instruments Inc., Montreal). Three cells per treatment were also transplanted into 8-inch pots to stimulate field transplanting. Based on mean separation tests (n = 30), increased cell volume before transplanting significantly increased root surface area, average diameter, and root volume after transplanting (n = 18). Mean root surface area for a 29-mL cell was 30% greater than a 15-mL cell before transplanting and 22% greater after transplanting. Plug cell volume also significantly impacted shoot and root biomass (P <0.0001). A 14-mL increase in cell volume resulted in a root and shoot dry weight increase of about 15%.

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Milton E. Tignor Jr. and Russell L. Weiser

Alaska peas (Pisum sativum `Alaska') were germinated in the dark at 25C. After three days, when the shoots were approx. 1.5 cm, treatments were initiated. ABA, at 10-4M, was exogenously applied through the root solution. The control peas remained in distilled water. All treatments involving the application of ABA were applied under green safe light. Light treatments were applied using overhead fluorescent lights for designated timed intervals (0 to 20 min) over 3 days. A methanol bath was then used to induce freezing stresses from 0 to -9C. The combination treatment of light and ABA had the lowest LT50 (more cold tolerant) followed by light, dark, and dark with ABA (least cold tolerant). Extensin levels, plant growth, and stem bendability were also recorded.

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Milton E. Tignor Jr. and Russell L. Weiser

Alaska peas (Pisum sativum `Alaska') germinated in a dark growth chamber were treated ABA dissolved in a small amount of acetone before diluting in distilled water with 0.1% spreader. A blank solution was identically prepared without ABA. Both solutions were applied via paintbrush to the epicotyls of the peas every twelve hours for seven days following emergence. The blank solution was applied to two controls, chronological and physiological. A methanol bath was used to induce freezing and chilling stresses. ABA significantly improved cold tolerance (electrolyte leakage) in the pea seedlings for both freezing and chilling stress as compared to the physiological and chronological controls. Visual observation of the pea stems suggested a difference in stem flexibility among ABA treated peas and the controls. Pea stem elasticity and plasticity were measured along with plant dry weight, cell wall weight/gram fresh weight, and the quantity of cell wall sugars and amino acids.

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Milton E. Tignor and Peter J. Stoffella

Florida citrus has had an average annual on-tree-value of ≈1 billion dollars during the past decade in Florida. Nearly all of the 845,260 acres of citrus in Florida is produced on grafted trees consisting of a commercial scion cultivar and a rootstock selected specifically for local soil, environment, and pest pressures. With vastly different root-zone environments, ranging from deep sands to drained and cleared pine Flatwoods, a large number of different rootstocks are utilized. These rootstocks are started from seed at more than 100 commercial nurseries statewide, which currently produce an estimated 6 million trees a year. Although the optimum germination conditions, basic physiological performance, and adaptability of many rootstocks are known, there has been minimal investigation on early root development in seedling trays at the nursery. Four hundred seedlings of `Swingle' citrumelo (Citrus paradisi Macf. `Dunacn' × Poncirus trifoliata), `Smooth Flat Seville', `Volkamer' lemon (Citrus volkameriana), and `Sun Chu Sha' mandarin were seeded in a randomized block experimental design and grown at a commercial nursery. Seedling root systems (100/rootstock) were analyzed for a number of variables using the Rhizo (Regent Instruments, Inc.) software package and a dual light source scanner. Using the SAS general linear model procedure, hypothesis testing revealed rootstock selection had a significant effect on total root length, total root surface area, total root volume, number of root tips, number of root forks, root dry weight, and stem diameter. For most characteristics, rootstock genotype accounted for a greater portion of variability than samples (plant to plant variability).

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Milton E. Tignor and Sandra B. Wilson

Information is more accessible to students than ever before. Gone are the days of a single instructor being the ultimate authority on a specific scientific discipline. Search engines, online journals, virtual libraries, and the development of Internet II will continue to drive the increase in availability of information. With basic computer skills, the average college student can put their hands on more subject data than they could possibly read during the time frame of a semester-long course. Therefore, it is more critical than ever to give students the logical tools to evaluate information and construct intelligent arguments. One particular area of interest to the horticulture industry is the impact of environmental regulations and public concern over common horticultural production practices such as irrigation, land development, application of pesticides, and developmental manipulation using growth regulators. South Florida is a mosaic of pristine natural areas, major agricultural production regions, densely populated urban areas, and regions of rapid suburban growth. As a result, there is heightened public awareness of environmental issues, which often leads to spirited conflicts among people with diverse professional backgrounds and personal interests. This catalyzed the development of a new course entitled “South Florida Flora and Ecosystems” that uses several different types of critical thinking exercises to help relate course content information into the cultural and political framework of South Florida. Techniques such as role playing, utilizing guest speakers with opposite opinions on the same topic, and active evaluation of data were used to enhance student learning, increase environmental awareness, and place undergraduate horticultural students one step closer to becoming “society-ready” graduates.

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Milton E. Tignor Jr. and Courtney A. Weber

Current efforts in the study of citrus freeze hardiness including gene mapping and elucidating early induction processes require large populations of uniform seedlings. Related genera and intergeneric hybrids are often used in these studies and little is known about factors effecting their seedling emergence. We tested a total of 8 genotypes including Poncirus trifoliata `Rubidoux', Citrus grandis, C. sinensis `Pineapple', C. jambhiri `Schaub', C. paradisi `Duncan', C. aurantium (Brazilian), Carrizo citrange (P. trifoliata × C. sinensis), and Troyer citrange. A total of seven pre-planting treatments were used to evaluate seedling emergence rates. Expanding on the work of previous researchers, treatments were seed coat removal, hydrating in water (96 hours) at either 4, 25, or 35°C, acid scarification, or boiling. Generally, seed coat removal resulted in the most uniform emergence as compared to untreated controls. Presoaking at each temperature enhanced emergence in most varieties tested and 25°C was the best hydrating temperature. Acid scarification greatly delayed emergence in all genotypes tested except Troyer citrange and `Pineapple' orange which had enhanced emergence rates as compared to controls. Preplanting treatment with 100°C water was lethal in all varieties. Pretreatment of citrus seeds can enhance uniformity of germination, although optimum treatments for individual genotypes vary.

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Milton E. Tignor Jr. and Elizabeth M. Lamb

The Univ. of Florida has had off-campus degree programs for over a decade. In 1998, a new program in a major agricultural region of the state developed under unique circumstances. Community driven support, leadership from local politicians, and guidance from academic administrators resulted in the legislative funding of a new undergraduate teaching program in south Florida. The program offers upper-division courses leading to Bachelor of Science degrees in horticultural science and food and resource economics. Another unique aspect was the partnership formed with local universities necessary to offer the degrees. Locally, Indian River Community College provides lower-division courses and Florida Atlantic Univ. offers four upper-division courses to complete the course offerings for the degrees. Funding was allocated for eight new faculty members with 70% teaching appointments, four support staff, and a new $3.7 million teaching complex. In today's academic climate, having eight new faculty members at one time is a rare occurrence that allowed for creative growth on the part of the new teaching program. What was successful and unsuccessful concerning recruitment, advertising, purchasing, advising, collaborative efforts with local colleges, and administration will be discussed. In addition, demographics on the student body will be presented.

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Milton E. Tignor, Frederick S. Davies, and Wayne B. Sherman

Two USDA intergeneric, hybrid citrus scions, US 119 {[Citrus paradisi Mac. `Duncan' × Poncirus trifoliata (L.) Raf.] × C. sinensis Osb. `Succory'} and selection 17-11 {C. grandis US 145 × [Citrus paradisi Mac. `Duncan' × P. trifoliata (L.) Raf.]} on `Swingle' citrumelo (C. paradisi × P. trifoliata) rootstocks were examined for freeze hardiness traits (4 years) and general growth characteristics (2 years). Hardiness was compared with that of `Hamlin' orange [C. sinensis (L.) Osb.] and satsuma mandarin (C. unshiu Marc) from Fall 1993 to Spring 1997. As expected, US 119 and 17-11 were both hardier than `Hamlin' orange as determined by leaf disc electrolyte leakage (EL). Both showed freezing tolerance similar to that of satsuma mandarin, but 17-11 was significantly hardier than satsuma or US 119 at several times during the 4-year study. Trunk diameter and tree height were similar for US 119 and selection 17-11.

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Milton E. Tignor Jr., Frederick S. Davies, and Wayne B. Sherman

Citrus hybrids USDA 17-11 [Citrus grandis L. × (C. paradisi Macf. `Duncan' × Poncirus trifoliata (L.) Raf. `Gotha Road')] and 119 [(C. paradisi Macf. `Duncan' × P. trifoliata (L.) Raf. `Gotha Road') × C. sinensis (L.) Osb. `Succory'], `Hamlin' orange [C. sinensis (L.) Osb.], and satsuma mandarin (C. unshiu Marc.) were planted March 1993 and 1994. Trees were irrigated and fertilized in an identical manner. In 1993, electrolyte leakage readings were taken monthly using 17-11, 119, and satsuma leaf discs. Leaf killing point (LKP) LT50 averaged from –8 to – 9C by mid-November for all selections. In 1994, leaf discs from 17-11, 119, and `Hamlin' orange were sampled weekly to determine LKP. USDA 119 had the lowest LKP and acclimated the fastest during the fall. By the end of November, there was no significant difference in LKP (–6.5C) between USDA 119 and 17-11, although both selections were significantly more freeze-tolerant than `Hamlin' orange (LKP–40C), which showed no significant decrease in LKP until the 6 weeks after the hybrid selections began acclimating. Citrus hybrids 17-11 and 119 can survive in freeze-susceptible areas that are marginal for other commercial citrus.

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Milton E. Tignor Jr., Frederick S. Davies, and Wayne B. Sherman

`Hamlin' orange trees [C. sinensis (L.) Osb.] from a commercial nursery were planted into raised beds on a site that simulated conditions typical of the flatwoods region of the citrus industry. A factorial experiment with three irrigation schedules, based on growth flushes and three nutrient application frequencies (total N, 0.136 kg/tree per year), was conducted in 1994. Trees were irrigated using 90° microsprinklers, and soil moisture content was monitored using a neutron probe. Eleven replicate trees of the nine treatments were included in a completely randomized block design. Weekly freeze tests using the electrolyte leakage method were conducted at –4, –6, and –8C. Electrolyte leakage was determined using a conductivity meter. Different irrigation scheduling based on growth flushes had no significant effect on freezing acclimation. However, increased frequency and lower amounts of fertilizer per application significantly (P = 0.05) increased freeze hardiness from 4.2 to –6.10C by the end of November. Morphological data including trunk diameter, tree height, and flushing status also were recorded. Increasing frequency of nutrient application resulted in a more rapid acclimation of young `Hamlin' orange trees.