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Inmaculada Moreno-Alías, Hava F. Rapoport, Rafael López, Lorenzo León, and Raúl de la Rosa

et al., 1976 ; Zimmerman, 1977 ) and, more recently, olive ( De la Rosa et al., 2006 ; Pritsa et al., 2003 ; Rallo et al., 2008 ). In this latter species, early elimination of plants with a long juvenile period is based on plant height measured

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Martín Mata-Rosas, Rosario Julieta Baltazar-García, and Victor Manuel Chávez-Avila

increasingly common ( Ávila-Díaz et al., 2009 ; Damon et al., 2004 ; Lee-Espinosa et al., 2007 ; Mata-Rosas and Salazar-Rojas, 2009 ; Mata-Rosas et al., 2010 ; Santos-Hernández et al., 2005 ). Nevertheless, it is critical to establish new protocols for

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Milad El Riachy, Luis Rallo, Raúl de la Rosa, and Lorenzo León

2009: R 2 = 0.72). Significant correlation between height and diameter measurements in olive seedlings has been previously reported ( De la Rosa et al., 2006 ; Rallo et al., 2008 ). Solarization produced a significant increase in trunk diameter in

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Barbara C. Poole, Terril A. Nell, and James E. Barrett

Premature flower bud abscission imposes a serious limitation on longevity of potted Hibiscus in interiorscape situations, Ethylene is known to be one causative factor. Past research has suggested that carbohydrate depletion of buds may also be involved,

A series of experiments was conducted to examine the relationship between carbohydrate levels and ethylene sensitivity of flower buds under low irradiance levels. Two cultivars were used: `Pink Versicolor', which is very susceptible to bud abscission, and the more resistant `Vista', In the first experiment, plants were harvested twice weekly after placement in interiorscape rooms (8.5 μmol m-2 s-1 for 12 hrs per day; 26.5°C day/night) until all buds had abscissed. At each harvest, buds from four size groups were collected for analysis. In the second experiment, source/sink strength of buds was manipulated by selective daily removal of certain sized buds. Remaining buds were collected just prior to abscission for analysis. In two additional experiments, `Pink Versicolor' plants were treated with either silver thiosulfate or ethephon prior to placement in interiorscape rooms. Plants were harvested twice weekly and buds collected. For all experiments, bud dry wt, total soluble sugars and starch content were determined.

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Barbara C. Poole, Terril A. Nell, and James E. Barrett

Premature flower bud abscission imposes a serious limitation on longevity of potted Hibiscus in interiorscape situations, Ethylene is known to be one causative factor. Past research has suggested that carbohydrate depletion of buds may also be involved,

A series of experiments was conducted to examine the relationship between carbohydrate levels and ethylene sensitivity of flower buds under low irradiance levels. Two cultivars were used: `Pink Versicolor', which is very susceptible to bud abscission, and the more resistant `Vista', In the first experiment, plants were harvested twice weekly after placement in interiorscape rooms (8.5 μmol m-2 s-1 for 12 hrs per day; 26.5°C day/night) until all buds had abscissed. At each harvest, buds from four size groups were collected for analysis. In the second experiment, source/sink strength of buds was manipulated by selective daily removal of certain sized buds. Remaining buds were collected just prior to abscission for analysis. In two additional experiments, `Pink Versicolor' plants were treated with either silver thiosulfate or ethephon prior to placement in interiorscape rooms. Plants were harvested twice weekly and buds collected. For all experiments, bud dry wt, total soluble sugars and starch content were determined.

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Robert H. Stamps and Annette L. Chandler

Desiccation of containerized plants at retail outlets due to inadequate watering is a recurring problem. Water stress can decrease plant quality and survivability. Treatments that could reduce plant transpiration without lowering plant quality could be beneficial in maximizing the likelihood that plants would not become water stressed between waterings at retail outlets. Abscisic acid (ABA) is known to be involved in the regulation of stomatal aperatures, the major control mechanism for transpirational water loss. Containerized plants of four cultivars of hibiscus were thoroughly sprayed with S-ABA at concentrations of 0, 125, 250 or 500 mg·L–1. Plants were held under simulated retail conditions and were not watered until visible wilting occurred. Transpiration and pot weights were monitored over time. Transpiration rates and weight loss percentages were negatively correlated with S-ABA concentrations. Effects on transpiration rates lasted for at least 30 hours after treatment. For mean hours to wilt, there was interaction between S-ABA treatments and cultivars. For the most sensitive cultivar (`Double Apricot'), treatment with S-ABA at 500 mg·L–1 almost doubled the time to plant wilt (130 h) compared to the control treatment (72 hours). Hours to wilt was increased 24% for `Double Pink' treated at the highest rate. For `Double Red' and `Single Pink', hours to wilt was not affected by treatments. For some hibiscus, S-ABA treatments prior to placement of plants at retail outlets might decrease the chances that the plants would become severely water stressed.

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Andrew D. Cartmill, Fred T. Davies Jr., Alejandro Alarcon, and Luis A. Valdez-Aguilar

Sustainable horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to problems associated with high levels of bicarbonate (HCO - 3) and associated high pH in irrigation water. The ability of arbuscular mycorrhizal fungi (AMF; GlomusZAC-19) to enhance plant tolerance to HCO3 - was tested on the growth, physiology and nutrient uptake of Rosamultiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and noninoculated (non-AMF) plants were treated with 0, 2.5, 5, and 10 mm HCO - 3. Increasing HCO - 3 concentration and associated high pH and electrical conductivity (EC) reduced plant growth, leaf elemental uptake and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO - 3 as indicated by greater plant growth, leaf elemental uptake (N, P, K, Ca, Fe, Zn, Al, Bo), leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower wall-bound ACP (at 2.5 mm HCO3 -), and higher soluble ALP (at 10 mm HCO3 -). While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO - 3 concentration, colonization still occurred at high HCO - 3. At 2.5 mm HCO3 -, AMF plant growth was comparable to plants at 0 mm HCO3 -, further indicating the beneficial effect of AMF for alleviation of HCO3 - stress.

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Luis Alonso Valdez-Aguilar and David William Reed

Response to alkalinity was evaluated in two hibiscus cultivars, Bimini Breeze and Carolina Breeze, grown in a soilless growing medium and in hydroponic culture. For soilless growing medium, plants were potted in a sphagnum peat–perlite-based substrate and irrigated with solutions containing 0 to 10 mm NaHCO3 for 12 weeks. In hydroponic culture, bare-rooted plants were transferred to a 9-L tray containing a Hoagland's nutrient solution prepared with NaHCO3 at the concentrations previously indicated. In soilless growing medium, shoot dry weight was minimally affected by NaHCO3 concentration for `Bimini Breeze', but `Carolina Breeze' exhibited a significant decrease in shoot mass with increasing NaHCO3 concentration. In hydroponic culture, increasing concentration of NaHCO3 induced a decrease in shoot and root mass in both cultivars, but root mass decrease was more pronounced in `Bimini Breeze'. In soilless growing medium, increasing the concentration of NaHCO3 caused an increase in growing medium pH. The pH increase was less pronounced for `Bimini Breeze' than for `Carolina Breeze', indicating a higher capacity for root zone acidification by `Bimini Breeze'. Newly developed leaves of both cultivars showed increasing chlorosis with increasing NaHCO3 concentration. However, `Bimini Breeze' was more tolerant because, according to regression models, 5.7 mm NaHCO3 would be required to reduce chlorophyll levels by 10%, compared with 2.2 mm for `Carolina Breeze', when grown in soilless medium. Fe reductase activity decreased when `Carolina Breeze' plants were grown in 5 mm NaHCO3. However, in `Bimini Breeze', Fe reductase activity was enhanced. These observations indicate that the increased tolerance of `Bimini Breeze' to increasing alkalinity is the result of enhanced Fe reductase activity and increased acidification of the root zone.