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W.C. Lin, G.S. Block, S. Chen, and D.L. Ehret

In commercial production of greenhouse cucumber, moderate water stress is often undetectable until plants show severe wilting. The purpose of this study was to establish a noncontact, early detection method for such moderate stress before visual wilting takes place. An infrared imaging system including an infrared camera, a personal computer, and necessary image processing software was placed in a greenhouse with the camera elevated and viewing the plant canopy. Selected plants, each in a bag of sawdust growing medium, were subjected to water stress by removing irrigation tubes from the growing medium. The infrared images obtained from a crop canopy displayed an increase in foliar temperature of stressed plants, which were located among normally watered (control) plants in the same greenhouse. Increased foliar temperatures of stressed plants occurred 1 to 3 days before wilting was observed. When visual wilting occurred, the stress treatment was stopped and irrigation was resumed within the same day. Cucumber plants showed no crop loss after one cycle of moderate stress. Repeated moderate stress caused yield loss. The potential applications of this nondestructive, noncontact detection method in plant science research and in commercial greenhouse production will be discussed.

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N.K Lownds, M.G. White, and R.D. Berghage

Previous work has shown that container grown landscape plants use, and likely need, much less water than is typically applied. Therefore, studies were conducted to quantify the relationships between water loss and water stress responses using several drought tolerant (Cassia corymbosa, Leucophyllum frutescens, Salvia greggii) and traditional landscape plants (Euonymus japonicus, Pyracantha coccinea). Water stress was induced by withholding water and water loss measured gravimetrically. The shape of the water loss curve was similar for all species being, Y = a + bx + cx2 (r2 > 0.95). The rate of ethylene production began to increase 24 hr after irrigation, reaching a maximum 36-48 hr after irrigation and then decreasing. Maximum ethylene production occured at 35-47% water loss irrespective of species or rate of water loss. Stress symptoms (wilting leaf discoloration and abscission) followed a similar pattern. The potential for monitoring gravimetric water loss to schedule container irrigation will be discussed.

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N.K Lownds, M.G. White, and R.D. Berghage

Previous work has shown that container grown landscape plants use, and likely need, much less water than is typically applied. Therefore, studies were conducted to quantify the relationships between water loss and water stress responses using several drought tolerant (Cassia corymbosa, Leucophyllum frutescens, Salvia greggii) and traditional landscape plants (Euonymus japonicus, Pyracantha coccinea). Water stress was induced by withholding water and water loss measured gravimetrically. The shape of the water loss curve was similar for all species being, Y = a + bx + cx2 (r2 > 0.95). The rate of ethylene production began to increase 24 hr after irrigation, reaching a maximum 36-48 hr after irrigation and then decreasing. Maximum ethylene production occured at 35-47% water loss irrespective of species or rate of water loss. Stress symptoms (wilting leaf discoloration and abscission) followed a similar pattern. The potential for monitoring gravimetric water loss to schedule container irrigation will be discussed.

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E. Peterlunger and B. Marangoni

141 ORAL SESSION 42 (Abstr. 289–295) Small Fruits/Viticulture: Nutrition and Stress Physiology

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Thammasak Thongket and James O. Garner Jr.

Responses of four sweetpotato genotypes (`Centennial', `Travis', `Vardaman' and `MS 21-2') to water stress were studied. Two irrigation regimes (irrigation vs non-irrigation) were imposed on five-week old cuttings grown in a greenhouse environment. Transpiration and leaf diffusive resistance (LDR) were measured with a steady state porometer and mid-day total leaf water potentials were determined with a thermocouple psychrometer. Leaf growth was inhibited earlier than root growth. Water stress caused a reduction of leaf size in Centennial and in leaf number in the other three. Storage root number of Vardaman was not inhibited by limited soil moisture but development of storage roots was retarded by water stress. Total growth under non-irrigation of MS 21-2 was inhibited more than Vardaman. Mid-day leaf water potential did not show promise as a good indicator of water status. Genotypic differences in the water stress sensitivity as measured by LDR, were observed.

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Andrew G. Reynolds and Andrew P. Naylor

Glasshouse-grown `Pinot noir' and `Riesling' grapevines (Vitis vinifera L.) were subjected to one of four water stress durations [no water deficit (control); and water deficits imposed postbloom, lag phase, and veraison] in combination with three soil water-holding capacities (0%, 26%, and 52% gravel, by volume). Vines subjected to increasing water stress duration had less cumulative lateral shoot length and lower shoot count, leaf size, and berry weights than those not stressed. Soluble solids concentration (SSC) during maturation and pH at harvest also increased with increasing water stress duration, but titratable acidity was not affected. Transpiration and stomatal conductance also were reduced with increased water stress duration, but soil water increased, reflecting the larger leaf surface on vines with veraison-imposed deficits. Reducing water-holding capacity (by increasing the percentage of gravel in the soil) tended to increase berry weight and SSC but reduced lateral shoot growth. The 52% gravel treatments increased transpiration rate and stomatal conductance for `Riesling' but reduced them slightly in `Pinot noir'. Percentage of soil moisture was reduced linearly with reduced water-holding capacity. These results indicate that early irrigation deficits may advance fruit maturity of wine grapes with concomitant reductions in vegetative growth. Differential responses of these cultivars to soil water-holding capacity also should help to identify suitable wine grape cultivars as the wine grape industry expands into areas with low water-holding capacity soils.

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Zhongchun Wang and Gary W. Stutte

31 ORAL SESSION 4 (Abstr. 027–033) Fruits and Nuts: Stress Physiology

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Roger Kjelgren and Bradley H. Taylor

86 ORAL SESSION (Abstr. 512-519) CROSS-COMMODITY STRESS PHYSIOLOGY

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Jerriann Ernstsen, Larry Rupp, and Ray Brown

Typically, dormant seedlings are transplanted when revegetating disturbed lands to prevent transplant shock triggered by water stress. It may be possible to transplant nondormant seedlings by inducing drought-tolerant acclimation responses such as solute accumulation. Artemisia cana and Agropyron intermedium seedlings were subjected to three different water stress preconditioning treatments. After conditioning, seedlings were dried down in their containers until leaf senescence, or were transplanted to disturbed land sites. Leaf water potential components and relative water content were measured. Following treatments, water relations parameters of preconditioned seedlings were not markedly different from controls in either species. At the end of the final dry-down, water stress preconditioning had not induced active or passive solute accumulation, prolonged leaf survival during lethal drought conditions, or differences in transplant survival under the experimental conditions of this study.

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J.W. Buxton and T.D. Phillips

Students in plant science courses have difficulty thoroughly understanding the effect of water stress on net photosynthesis and its consequences—reduced plant growth, productivity, quality, and profit. A laboratory demonstration utilizing a controlled water table irrigation system (CWT) provides a nearly constant plant water potential. Pots are placed on a capillary mat with one end suspended in a trough with nutrient solution. The vertical distance from the solution surface to the pot bottom determines the water potential; the water potential is 0 when the pot bottom is at the same level as the nutrient solution. The greater the vertical distance from solution to the pot bottom, the lower the water potential. For this demonstration, the bench was sloped from 0 to 10 cm above the solution over a distance of 90 cm. Corn, squash, soybean, fescue, and marigold seed were directly sown to either 9- or 15-cm pots and then placed on the CWT sloped bench at five vertical distances above the solution. Weekly, students observed plant growth and at the end of 8 weeks evaluated root and shoot growth. For all species, plant growth was indirectly related to the distance above the nutrient solution. Plants at near 0 water potential were much larger than those grown 8 to 10 cm above the solution.