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18 COLLOQUIUM 1 (Abstr. 990-994) Recent Advances in Plant Responses to Stress: Bridging the Gap Between Science and Technology

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We thank Larry Freeman and Keven Calhoun for their technical support and Speedling Inc., Blairsville, Ga., for providing the plant material.

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Tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in peat bags, rockwool slabs, and NFT in a greenhouse to examine the effects of nutrient solution electrical conductivity (EC) and potential evapotranspiration (PET)-dependent EC variation on plant water relations. Peat bags were irrigated by a PET-dependent irrigation system. EC was varied from 1 to 4 mS·cm-1 according to PET under –5 and –9 kPa of substrate water potential setpoints (SWPS). The plants in rockwool and NFT were treated with ECs of 2.5, 4, and 5.5 mS·cm-1. Peat bags and rockwool slabs were overwatered once a week to wash out the accumulated salts. Leaf water potential (ψ1) and relative water content (θ) were measured before and after plants were overwatered. Turgor (P) and osmotic π potentials were estimated from the pressure-volume method. Before plants were overwatered, ψ1 was significantly lower in the plants with high EC and low SWPS treatments and also lower in variable EC-treated plants, but P maintained close to the control value. After plants were overwatered, ψ1 recovered close to the control level and P became higher because of the lower π in the treatments of high EC, variable EC, and/or low SWPS. At a given ψ1 the plants with high EC, variable EC, and/or low SWPS maintained higher θ. The analysis of the pressure-volume curve showed that the leaves treated with high EC, variable EC, and/or low SWPS had higher turgid water content, higher symplasmic (osmotically active) water content, lower apoplasmic (osmotically inactive) water content, and lower θ point of zero turgor (incipient plasmolysis). Maintenance of P after overwatering was directly proportional to photosynthetic capacity. We suggest that osmotic adjustment occurs in response to high EC, low SWPS, or both and that overwatering substrates and varying EC can not only avoid salinity stress, but also improve turgor maintenance.

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Abstract

The CO2 exchange rates of Peperomia obtusifolia A. Dietr. plants (tops and roots) were measured for 12-hour light and 12-hour dark cycles during 5 weeks of acclimatization at 30 µEs-1m-2. A carbon balance analysis of the data indicated that the growth conversion efficiency (Yg) remained constant (0.73 ± 0.1 and 0.77 ± 0.04 before and after acclimatization, respectively). The daily rate of substrate production from photosynthesis (ΔS/Δt) remained constant at 18 ± 2 mg C plant-1 24 hr-1, at the acclimatization photosynthetic photon flux density (PPFD), but the daily rate of synthesis of carbon into new material (ΔW/Δt) increased by 55% within the first week. The maintenance coefficient (m) decreased from 13.0 ± 0.9 to 7.4 ± 0.4 mg g-1 24 hr-1, and change in m may be a criterion for selection of plants that can be adapted for use at low PPFD. The light compensation point (LCP) was reduced during acclimatization, but its use underestimated the PPFD required for 24-hour plant maintenance because of failure to account for night-time respiratory losses. It is suggested that the PPFD at which ΔW/Δt is zero or slightly above is more reliable than the light compensation point for determining PPFD required for plant maintenance.

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Abstract

Several species of Leucophyllum are widely used in Texas and the southwestern United States (Arizona, California, Nevada, New Mexico) for amenity plantings. These taxa are among the most ornamental of all native Texas plants (8). Leucophyllum candidum I. M. Johnst. (2, 7) grows on arid sites in northern Mexico and in southern Brewster Co., Texas, and is usually found on caliche, gravelly hillsides (11). The low requirements for nutrients, water, pest control, and general maintenance make the use of ‘Thunder Cloud’ a pragmatic choice for water and energy conservation in the arid to semi-arid southwest (12).

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Sixty-six perennial ornamental cultivars were established and then grown under low maintenance, intensive weed competition, and severe mowing conditions. These cultivars were evaluated for their potential application for roadside/median beautification. Experimental plots were cleared with Roundup® prior to planting. During the first 3 weeks of establishment, plants were irrigated as needed. Plants were grown for one season, then pruned back to simulate bush-hog mowing. Plants were grown under low maintenance and no weed control conditions for two growing seasons. Plants were evaluated each season for simulated bush-hog damage recovery potential, survivability under severe weed competition, height, and spread. Two-way analysis of variance with repeated measurements showed that height and spread variation had a significant interaction between plant cultivar and time of evaluation. Several Zephyranthes sp. cultivars performed poorly under severe weed competition and mowing damage resulting in a high mortality rate. Cultivars that did perform well for the 2-year evaluation period include Lagerstroemia indica ×fauriei `Natchez,' Lagerstroemia indica ×fauriei `Muskogee,' Vitex agnus-castus `Shoal Creek,' and Myrica cerifera. Rosa × `Chuckles' and Rosa × `Knock Out' cultivars, with their popular showy appearance, performed moderately well and showed high potential for roadside/median beautification applications.

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The University of Hawaii at Manoa campus offers a rich diversity of plants for students, university personnel, and the public. Although providing botanical facts, a current university web site and an arboretum brochure about campus plants lack horticulturally related information. By highlighting the unique horticultural plants on campus, a web site would provide valuable information on the uses, care, and propagation of these plants. The purpose of this project was to develop a web site featuring horticulturally important plants on campus. The home page explains why plants are beneficial in interior spaces. Other sections of the web site include basic plant care, plant selection, plant names, and plant pictures. Basic plant care covers planting media, containers, watering, lighting, fertilizing, pruning, propagation, and pest control. Users can select plants using two criteria—lighting in the plant's desired location (low, medium, and high) and low plant maintenance. Information on a specific plant is accessed by common name, scientific name, or a plant's picture. Each plant's web page provides details on its background, care, and propagation. By emphasizing the important horticultural plants on campus, this web site helps students, university personnel, and the public select and grow plants for their dormitories, apartments, offices, and homes. In addition, users gain knowledge about the lush landscape environment on campus. Lastly, the web site enhances the learning experience of students in horticulture and botany courses, serves as a resource for K–12 students for their visits to the campus to learn about tropical plants, and aids tourists in planning a more informative visit to campus to see the plants they learned about on the web site.

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Abstract

Malus × ‘Naragansett’ combines multiple disease resistance and superior ornamental characteristics for reduced landscape maintenance. Crabapples are of utmost significance to the nursery industry, landscape architects, and gardeners alike as they are the most versatile and widely cultivated small landscape tree throughout the northern United States and southern Canada. ‘Naragansett’ is a noteworthy addition to the long list of crab-apple cultivars, as very few combine disease resistance and superior landscape characteristics. In the recent survey by Nichols (2), only three of the 48 recommended cultivars, species, and varieties of the more than 700 surveyed were disease free, while the other 45 displayed varying degrees of resistance or tolerance. ‘Naragansett's’ growth habit is in scale with many landscape situations, and the plant requires low maintenance due to its open branch structure and disease resistance.

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For the past 5 years, we have evaluated more than 100 herbaceous perennial groundcovers, including both grasses and grass mixtures, as well as ornamental broadleaf materials, for their ability to establish, suppress weeds, provide aesthetic appeal, and resist pests in various landscape and roadside settings across New York State. By working in cooperation with the NYSDOT, we have developed recommendations for materials that have performed well in difficult, potentially stressful, roadside and landscape settings. We have performed replicated research and demonstration trials that have clearly shown that certain species and cultivars provide effective weed suppression; great aesthetic appeal due to foliar texture, color, or flowering, resist pests and diseases; and require low maintenance over time. In addition, certain materials tolerate high levels of salt (NaCl), simulating roadside salt application exposure, in supplemental greenhouse studies. Materials generally suppressed weeds effectively by forming a dense canopy in a short period of time, and reducing light interception at the soil surface under this dense canopy. Certain groundcovers also appeared to exhibit strong potential allelopathic properties when grown either in field or laboratory settings. The selection of new plant materials for use in low-maintenance landscape settings offers potential to reduce time and maintenance inputs in difficult landscape or roadside settings, with the added benefit of reducing pesticide application in these settings for weed management. Additional studies are currently underway to develop further recommendations for use of warm- and cool-season turfgrasses in these settings.

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Oral Session 32—Ornamental/Landscape/Turf/Plant Breeding/Management 30 July 2006, 2:00–3:15 p.m. Oak Alley Moderator: Timothy Rinehart

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