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A.M. Shirazi and M.V. Thierry

It is not well known how cold-hardy new buds and emerging leaves or flowers are during spring. Extreme temperature fluctuations that sometimes bring early frost in spring (April–May) are very common in northern latitudes and cause severe damage to emerging leaves and flowers. Even though most woody plants can tolerate frost in spring, others show early tissue damage and can fully recover. There are some trees, e.g., Japanese maples (Acer palmatum) that when leaves are damaged due to spring frost, the results include severe dieback and eventual death. We tested new flowers and leaves of four crabapples: Malus ×micromalus, M. sargentii, `Mary Potter', and M. hupehensis, after budbreak for 3 years using electrical conductivity (EC) and differential thermal analysis (DTA) in spring: May 1997, Apr. 1998, and Apr. 2000, at The Morton Arboretum. Both flowers and leaves can tolerate from –6 to –12 °C and we observed higher ion leakage in leaves than flowers. The high temperature exotherm (HTE) of flowers were –8 to –10 °C in April. In a companion study, testing other species that had premature budbreak due to “near lethal” (sublethal) freezing stress in Jan. 2001, the following HTE were observed: Cornelian cherry (Cornus mas) flower (about –7.5 °C), Spindle trees leaves (about –6 °C), Judd's viburnum (Viburnum ×juddii) (about –8 °C), Brevipetala witch-hazel (Hamamelis mollis`Brevipetala') flower (about –5 °C), redbud (Cercis candensis) flower (about –9 °C), flowering quince (Chaenomeles ×superba) flower (–8 °C). Multiple LTE at –13, –18, –22, and –27 °C were observed for Judd's viburnum. This information could be useful for selection and breeding of woody plants.

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A.M. Shirazi and M.V. Thierry

Survival of temperate plants is often dependent upon their resistance or ability to tolerate low temperatures. Differential thermal analysis (DTA) has been employed to explore the freezing characteristics of plants and other organisms. However, there appears to be a need for further studies to better understand the physiology of freezing and its significance as related to supercooling. Methods employing thermocouples, differential wiring, and digital data acquisition boards allow detection of very small exothermic responses (about 0.025 °C). This study reports on techniques and apparatus for using DTA as well as results obtained on various plant tissues. When Fagus grandifolia (American beech) was compared to Fagus sylvatica (European beech), it exhibited both a lower high temperature (HT) and low temperature (LT) exotherm that correlated with lower stem tissue water content during September to May. The DTA on Acer pseudosieboldianum (Korean maple) from a higher elevation showed lower LT exotherm in stem tissues when compared to lower elevation samples. Incubation of Cornus amomum, Cornus obliqua, and Larix gmelinii var. olgensis stem tissue with d-H20 for 20 hours resulted in an induction of LT exotherm at a significantly higher temperature than a normal LT exotherm. This phenomenon was attributed to the bark tissue in Larix gmelinii var. olgensis. Sucrose and glycerol exotherm profiles exhibited lower exotherm temperatures. In a companion study, we used thermal analysis (non-differential) to study supercooling in [Homadaula anisocentra(Mimosa webworm)] and a single exotherm event was detected. New technology provides a great deal of flexibility in the method of evaluation of exothermic responses in plants and other organisms.

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A.M. Shirazi and K.A. Jacobs

Near-lethal abiotic stresses, e.g., low or high temperatures, chemicals, etc., can break endodormancy prematurely and reduce cold hardiness in woody plants. It is not well-ducumented whether biotic stresses can cause the same effect. Botryosphaeria dothidea causes canker in redbud (Cercis canadensis) and many other woody plants and is one of the most limiting factors growing redbud in the landscape. Two-year-old seedlings were planted in a nursery in May 1998 at The Morton Arboretum. Trees were inoculated (n = 10/treatment) with the fungus in Sept. 1998 using the stem slit method (a slit was cut about 5 cm above the base of the trunk and the wound was covered with parafilm after treatment). The treatments were T1 = control (PDA, Potato Dextrose Agar),T2 = 1-mm mycelium plug, T3 = low spore suspension (25 μL), T4 = high spore suspension (25 μL). Stem cold hardiness was evaluated by artificial freezing tests in Nov. 1998. The mean LT50 (the temperature at which 50% of the tissues is killed) from ion leakage were T1 (Control) = -29.3 °C, T2 (mycelium): -24.05 °C, T3 (low spore) = -18.75 °C, and T4 (high) = -16.4 °C. T3 and T4, the low- and high-spore inoculation, significantly reduced cold hardiness in redbud stem tissues. The LST (lowest survival temperature) based on visual observation of the samples after 7 days indicated all Botryosphaeria dothidea-treated plants had lower cold hardiness compared to control. Endodormancy was broken in B. dothidea-treated plants after placing plants under 16 h of light and 23 /18 °C day/night temperature for 1 month after the treatment. The highest percent budbrealk was for T4 (high spore), followed by T3 (Low Spore) and T2 (Mycelium).

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A.M. Shirazi and P.S. Muir

There is increasing interest in using methanol and other alcohol fuels as an alternative energy source in the United States and developing nations. However, methanol-fueled vehicles have higher direct emissions of formaldehyde (HCHO) than gasoline-fueled vehicles, which has led to concern about increases in atmospheric concentration of HCHO. Formaldehyde at concentrations of 300, 600, 900, and 1200 μM reduced germination of hydrated Douglas-fir (Pseudotsuga menziesii) pollen in vitro. HCHO concentrations and pH in media containing pollen decreased during the 25-h incubation, with decreases proportional to HCHO concentration. This effect was not seen with heat-killed pollen, which suggests a detoxification mechanism. Ion leakage (measured as electrical conductivity) of pollen increased within 20 h in all HCHO treatments compared to controls. Stress also was indicated by TTC staining, which also decreased after HCHO treatment compared to controls.

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A.M. Shirazi and L.H. Fuchigami

Previously, we reported that plant recovery from “near-lethal” (NL) (sublethal) stresses depended on stage of development and poststress environment (PSE). Dormant red-osier dogwood (Cornus sericea) plants exposed to NL heat, freezing, and hydrogen cyanamide either died or were severely injured when stored at 0C or recovered at 23C and nautral condition. Exposure of dormant stem tissues of red oak (Quercus rubra), paper birch (Betula papyrifera) and European mountain ash (Sorbus aucuparia), to heat stress also resulted in higher ion leakage when they were stored at 0C PSE for 3 weeks. Soaking NL-heat-stressed (49C for 1 hour) stem tissue of red-osier dogwood in double distilled water for 48 hours before incubating at 0C PSE for 2 and 12 weeks resulted in lower ion leakage and 80% tissue survival. NL-stressed tissue had higher sodium and similar potassium leakage at 0C PSE. At 23C, PSE NL stress had no effect on leakage of these specific ion.

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A.M. Shirazi and F.D. Miller

Research on silicon nutrition has shown an increase in plant disease resistance to powdery mildew and pythium in some species, such as roses and cucumbers. However, the role of silicon for protecting plants from other stresses e.g., heat, drought, insects, etc., are not known. Two-year-old Sargent Crabapple Malus sargentii seedlings were subjected to 4 continuous days of 100 ml root application of potassium silicate at the rate of 0, 100, 200, and 400 ppm in Aug. 1998. After 3 days post-treatment, three detached leaves were placed in each of three petri dishes along with one adult female Japanese beetle (n = 3/concentrations) for 7 days. Potassium silicate at 100 ppm concentration significantly reduced percent leaf tissue eaten by adult Japanese beetles. There was not any statistical difference between control, 200, and 400 ppm application. The ion leakage of stem tissues of 100 and 200 ppm-treated plants were significantly lower than the control and 400 ppm. These lower ion leakage effects were also observed with red-osier dogwood stem tissues at 100 ppm. In a companion study fall webworm larvae were also exposed to the same above concentrations and treatments. There was not a significant effect of potassium pilicate on percent leaf tissue eaten by fall webworm larvae, suggesting that there may be differences between major groups of leaf-feeding insects. Leaf and root tissue analysis for Ca, K, Mg, Na, and Si will be reported.

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A.M. Shirazi and G.H. Ware

The high resistance of Chinese elms to Dutch elm disease and elm leaf beetles makes them excellent trees for the urban landscape. There are many new Chinese elms being developed through the tree breeding program at The Morton Arboretum. Many new elms are already on the market or will be available soon from nurseries. There is little known about the stress tolerance, e.g., cold, heat, drought, etc., of new elms from China. The objectives of this study were 1) to determine the midwinter cold hardiness of new Chinese elms and 2) to determine the leaf heat tolerance and stem cold hardiness of new elms from the nursery. The stem cold hardiness of nine new elms from China was evaluated in Feb. 1998 and 1999 from the elm breeding program at The Morton Arboretum by using an artificial freezing test. The LT50 (the temperature at which 50% of the tissues were killed) of the most to least hardy genuses for Feb. 1998 were Ulmus macrocarpa (> -36 °C), U. wilsoniana # 673 (-34 °C), U. parvifolia R-89-120 (-34 °C), U. wilsoniana # 669 (-34 °C), U. wilsoniana # 997 (-33.8 °C), U. szechuanica (-30 °C), U. gaussenii R-94-85D (-30.7 °C), U. bergmanniana var. lasiophylla R-9422SD (-27.7 °C), and U. castaneifolia #R-9411-11-SD (-25.9 °C). Four new elms from Schmidt Nursery, Boring, Ore., were also evaluated for leaf heat tolerance in August and cold hardiness in Dec. 1998 and Feb. 1999. The LT50 of cold hardiness of stem tissues of cultivars in December were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (-23.5 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (-26.5 °C), U. Accolade™ (-33.5 °C), and U. Danada Charm™ elm (-31 °C). The LT50 of the most to least heat-tolerant cultivars were U. parvifolia `Emer 1' P.P. 7551, Athena® elm (53.8 °C), U. parvifolia `Emer 1' P.P. 7552 Allee® (52.1 °C), U. Accolade™ (50.8 °C), and U. Danada Charm™ elm (50.6 °C). Growth, dormancy development, spring budbreak, and performance of these cultivars will be compared.

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A.M. Shirazi and G.H. Ware

The genus Ulmus contains numerous stress-tolerant species, especially those from areas of China with climates similar to various regions of the United States. Lace-bark elm, Ulmus parvifolia, the true Chinese elm, has an extensive temperature distribution range in China and offers great promise as a street tree. The high resistance of this elm to Dutch elm disease and other elm problems makes it an excellent tree for urban landscapes. Two new U. parvifolia cultivars, Athena® and Allee®, are not cold hardy for northern climates and there is a need for new cold hardy lace-bark elms. Screening thousands of seedlings for cold hardiness, upright form, beautiful bark characteristics, and larger leaves will bring the most desirable U. parvifolia cultivars into the green industry. We determined that seed dormancy and the percentage of seed germination of four selected lacebark elms after 2 and 4 weeks were >30% and >50%, respectively. There were significant differences in stem cold hardiness among new lace-bark elms from China (about –32 to –40 °C). Laboratory determination of cold hardiness can provide great advantages over years of field testing. Response to the outdoor temperature in December, January, and February on a seed cold hardiness freezing test showed significant reduction in seed germination, especially at –30 °C. Freezing test of seeds to –40 °C, resulted in lt 50 of –3 to –5 °C in December, so, it is less likely that these U. parvifoilia will become invasive in northern latitudes. Invasiveness of these U. parvifolia for higher zones, e.g., 6–8 could be greater and selection of these elms is suitable for zones 5 and lower. Planting these elms in zones 4, 3, and 2 will give us useful information regarding their winter performance.

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A.M. Shirazi and C.P. Dunn

The Expressway Partnership (a project of the Chicagoland Chamber of Commerce's Gateway Green Committee) is an urban landscape project that promises to change the face of the city's expressways. The Morton Arboretum's Urban Horticulture Research Lab., with the support of ComEd (Excelon Corp.), since 2001 has been selecting, planting, and evaluating various cultivars of trees, shrubs, and ground covers in a search for the most suitable and sustainable plantings for the expressway environment. About 470 trees and shrubs were planted plus more than 10,000 groundcovers. In May 2002 these plants were visually evaluated and ranked from 1–5 with one being in excellent condition and 5 being dead. The control plants planted at Urban Horticulture Research Nursery at the Morton Arboretum had 100% survival. The survival rates for groundcovers were: Euonymusfortunei (Virginia Creeper) and Hemerocallis×daylily (day lily) had 80% to 90% survival rates, respectively. Pachysandra terminalis (Japanese spurge) plants died due to either de-icing salt sensitivity, or poor weed control. Syringa pekinensis (Peking lilac), as well as four Syringa cultivars, `President Grevy', `Summer Charm', `Charles Joly', and `James Mcfarlane', had a 100% survival rate. Survival rates for other plants were: Malus sargentii (Sargent crabapple) 93%; Robinapseudoacacia (black locust) ∼93%; Malus cultivars ∼75%; and Pinusbanksiana (jack pine) 75%. Cornussericea (red-osier dogwood) covered with 3 inches of mulch had a significantly better survival rate (90% to 100%) than the mulch treatment (60% to 80%). The growth and performance of other trees and shrubs will be also reported. This research will ensure sustainable and esthetic urban expressway plantings, while enhancing Chicago's stature as a significant urban landmark.