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Julio Solis, Arthur Villordon, Niranjan Baisakh, Don LaBonte and Nurit Firon

Drought stress represents a global constraint for sweetpotato production because most of the sweetpotato production occurs in semiarid regions ( Saraswati, 2007 ). Considering the complexity of the physiological and genetic mechanisms associated

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Fan Cao, Yunchu Wei, Xinwang Wang, Yongrong Li and Fangren Peng

increases the interests of the breeders and growers. For example, physiological stress resistance is one of the major goals of rootstock breeding. This study describes the drought stress resistance of the grafted young ‘Pawnee’ trees onto 12 different pecan

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Panayiotis A. Nektarios, Ioannis Amountzias, Iro Kokkinou and Nikolaos Ntoulas

especially profound during the drought stress periods. Substrate depth is the second constituent that has a direct effect on green roof weight, construction cost, and plant survival and growth. The influence of varying extensive green roof substrate depth on

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Manpreet Singh, Rupinder Kaur Saini, Sukhbir Singh and Sat Pal Sharma

with the current production systems are inevitable in the near future. Water shortages have frequently exposed crops to drought stress, which is often accompanied by heat and salinity stress. In contemporary agriculture, drought stress is, in fact, the

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Reagan W. Hejl, Benjamin G. Wherley, James C. Thomas and Richard H. White

under drought stress. Plant growth regulators such as TE [4-(cyclopropyl-a-hydroxymethylene)-3,5-dioxo-cyclohexanecarboxylic acid, ethyl ester] reduce turfgrass shoot growth by inhibiting the biologically active forms of gibberellins ( King et al., 1997

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Harry S. Paris, Peter J. Stoffella and Charles A. Powell

Summer squash (Cucurbita pepo L.) plants were grown in pots with high (290% capacity) or low (45% to 70% of capacity) soil moisture. The plants were exposed or not exposed to sweetpotato whiteflies (Bemisia tabaci Genn.). Only the plants exposed to whiteflies developed leaf silvering. Silvering was more severe in plants subjected to low soil moisture.

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Robert C. Ebel, James P. Mattheis and David A. Buchanan

Potted apple trees were severely (S) or moderately (M) droughted and compared to a well-watered control (C) to determine changes in biogenesis of leaf volatile compounds. Total available water (TAW) of the soil was allowed to decline to near 0% TAW, 20% TAW, and 100% TAW, for S, M and C, respectively, by the end of a two-week drying period. Twenty-nine volatile compounds were identified by GC-MS using headspace sampling of detached leaves. Concentrations of (E)-2-hexenal, (E)-2-hexenyl acetate, l-hexanol, (E)-2-hexen-1-ol and hexyl acetate were 5 to 310 times higher for S than C. It is suggested that the large drought induced increase in C-6 compounds was related to enhanced lipoxygenase activity.

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Sabrina L. Shaw, Rhoda Burrows and William F. Hayslett

Two year old sugar maples grown in 25 gallon containers were subjected to different levels of stress by withholding water. Drought levels were measured using irrometers. Irrometer readings of 40, 60, and 80 centibars were used to determine when to add water. The media used were a primary nursery mix of 50:50 sand and pine bark by volume. The maples were evaluated for differences in stomatal responsiveness with the porometer and growth parameters of number of nodes, internode length, and leaf number were taken. Some of the trees were treated with ROOTS as a drench to determine if it would enhance resistance to water stress of containerized nursery plants. Despite the use of ROOTS there was no significant difference between the stressed and the non-stressed plants of stomatal responsiveness or the growth parameters.

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Margaretha Blom-Zandstra and Klaas Metselaar

Strict legislation on the release of water and nutrients into the subsoil exists in the Netherlands. Therefore, on-line monitoring and control systems are being developed to tune the supply of water and nutrients to the plants' demand for optimal control of production and reduction of system losses. In this context sensors and control systems are important tools. For Chrysanthemum, however, the effect of reduced irrigation on crop production is not well understood and more data from adequate sensors are required to establish critical soil moisture levels for an optimal crop water status and growth. We studied the effect of different soil water levels and soil desiccation in a climate chamber and under changing light intensities in a greenhouse to assess the critical soil moisture status for optimal growth of Chrysanthemum plants. Moreover, we studied the efficacy of infrared (IR) thermometry as a useful tool for on-line monitoring and control under the conditions of Dutch greenhouse horticulture. It is shown in this study that under moderate climate conditions plants start to suffer from water shortage when soil moisture potential pF reaches values below –32 kPa. Water status of the plant can very well be monitored on-line in a greenhouse as changes in leaf temperature due to water shortage can be detected by IR thermometry, especially at summer radiation levels. In the climate chamber however, leaf temperature did not respond to changes in soil water status, suggesting that the environmental settings of the climate chamber are unsuitable for these kind of experiments. In two of the three experiments at different levels of global radiation a change in leaf temperature is explained by a change in water regime. We conclude that regression analysis of high frequency on-line IR monitoring may be a useful tool for expost analyses of irrigation regimes at high light intensities, and may lead to interesting insights in crop responses.

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Stefania De Pascale, Albino Maggio, Celestino Ruggiero and Giancarlo Barbieri

We irrigated field-grown celery (Apium graveolens L. var. dulce [Mill.] Pers. 'Tall Utah') with four concentrations of saline water, NSC (nonstressed control), SW1, SW2, and SW3, corresponding to EC of 0.5, 4.4, 8.5, and 15.7 dS·m-1, respectively, plus a nonirrigated control (NIC) and investigated the effects of the treatments on water relations, yield and ion content. In addition, we compared simultaneously plant response to both salt and drought stress by using a modified version of the threshold-slope model. Increasing salinity of the irrigation water reduced fresh and dry weights of the shoots, but increased the dry matter percentage in shoots. The marketable yield was moderately affected by salinity (25% reduction at EC 8.5 dS·m-1). In contrast, a severe water stress dramatically decreased the marketable yield from 23 t·ha-1 (average of the irrigated treatments) to <7 t·ha-1 (nonirrigated control). Na+ and Cl- concentrations increased in salinized plants whereas nitrogen content, K+, Ca2+, and Mg2+ concentrations decreased upon salinization. Midday leaf water potentials (Ψt) decreased from -1.48 MPa (0.5 dS·m-1) to -2.05 MPa (15.7 dS·m-1) and - 2.17 MPa (nonirrigated control), though the reduction in leaf cellular turgor was less severe. The maintenance of high leaf cellular turgor was positively correlated to a decrease in osmotic potential and to an increased bulk modulus of elasticity. These results indicate that it is possible to irrigate celery with saline water (up to 8.5 dS·m-1) with acceptable losses in marketable yield and confirmed that in the field, this species has the ability to efficiently regulate water and ion homeostasis. In the absence of irrigation, celery plants were unable to cope with the drought stress experienced, although this was comparable, in terms of soil water potential, to the one caused by saline irrigation.