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Nicole L. Waterland, John J. Finer, and Michelle L. Jones

Drought stress during shipping and retailing reduces the postproduction quality and marketability of potted plants. Plants respond to drought stress by closing their stomata and reducing transpirational water loss. This stress response is mediated by the plant hormone abscisic acid (ABA). Exogenous applications of s-abscisic acid (s-ABA), the biologically active form of the hormone, can enhance drought tolerance and extend shelf life in a variety of bedding plants. However, little is known about the effectiveness of s-ABA at enhancing drought tolerance in perennial crops like chrysanthemum (Chrysanthemum ×morifolium). ‘Festive Ursula’ chrysanthemum plants were drenched (0, 125, 250, or 500 mg·L−1) or sprayed (0, 500, or 1000 mg·L−1) with s-ABA. All applications containing s-ABA effectively delayed wilting by reducing stomatal conductance (g S). Shelf life was extended from 1.2 to 4.0 days depending on the concentration of s-ABA. Spray applications of 500 mg·L−1 s-ABA to six additional chrysanthemum cultivars increased shelf life from 1.6 to 3.8 days following drought stress. s-ABA treatment also allowed severely drought-stressed chrysanthemums to recover and remain marketable after rewatering. Growers can treat chrysanthemums with s-ABA to reduce water use during shipping and to delay wilting if plants are not adequately watered during retailing.

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Nicole L. Waterland, John J. Finer, and Michelle L. Jones

Drought stress during the shipping and retailing of floriculture crops can reduce postproduction shelf life and marketability. The plant hormone abscisic acid (ABA) mediates drought stress responses by closing stomata and reducing water loss. Applications of exogenous s-ABA effectively reduce water loss and allow a variety of species to survive temporary periods of drought stress. Unfortunately, s-ABA application can also lead to leaf chlorosis, which reduces the overall quality of economically important bedding plant species, including Viola ×wittrockiana (pansy). The goal of this research was to determine how to prevent s-ABA-induced leaf chlorosis in pansy and a closely related species, Viola cornuta (viola). All concentrations of both spray (250 or 500 mg·L−1) and drench (125 or 250 mg·L−1) s-ABA applications induced leaf yellowing. Young plants at the plug stage and 11-cm finished plants with one to two open flowers were further evaluated to determine if the developmental stage of the plants influenced s-ABA effectiveness or the development of negative side effects. Both plugs and finished pansies and violas developed leaf chlorosis after s-ABA applications, but symptoms were generally more severe in finished plants. The individual application of benzyladenine (BA), gibberellic acid (GA4+7), or the ethylene perception inhibitor, 1-methylcyclopropene, before s-ABA application had no effect on the development of s-ABA-induced leaf chlorosis. However, applications of 5 or 10 mg·L−1 BA and GA4+7 as a mixture (BA + GA4+7) before a drench or spray application of s-ABA prevented leaf chlorosis. The application of s-ABA and BA + GA4+7 would allow floriculture crops to tolerate temporary periods of drought stress without any loss of postproduction quality.

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Nicole L. Waterland, Craig A. Campbell, John J. Finer, and Michelle L. Jones

Drought stress is a major cause of postproduction decline in bedding plants. The plant hormone abscisic acid (ABA) regulates drought stress responses by mediating stomatal closure, thereby reducing transpirational water loss. Exogenous ABA applications delay wilting and allow plants to survive short periods of severe drought. The effectiveness of the ABA biochemical, s-ABA (ConTego™; Valent BioSciences Corp., Libertyville, IL), at delaying wilting and extending shelf life during drought stress was evaluated in six bedding plant species. Spray and drench applications of 0 or 500 mg·L−1 s-ABA were applied to Impatiens walleriana (impatiens), Pelargonium ×hortorum (seed geranium), Petunia ×hybrida (petunia), Tagetes patula (marigold), Salvia splendens (salvia), and Viola ×wittrockiana (pansy). Water was subsequently withheld and wilting symptoms were compared between treated and control plants. s-ABA applications delayed wilting in all crops by 1.7 to 4.3 days. Leaf chlorosis was observed after s-ABA application in drought-stressed seed geraniums, marigolds, and pansies. In seed geraniums and marigolds, the drought stress itself resulted in leaf chlorosis that was equivalent to or more severe than the s-ABA application alone. In pansies, s-ABA applications induced leaf chlorosis that was more severe than the drought treatment. Overall, s-ABA was consistently effective at reducing water loss and extending shelf life for all species treated. Applications of s-ABA to bedding plants before shipping and retailing would allow plants to maintain marketability even under severe drought stress conditions.

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L. Mark Lagrimini, Jill Vaughn, John Finer, Karen Klotz, and Patrick Rubaihayo

Tomato plants (Lycopersicon esculentum cv. OH 7814) were transformed via Agrobacterium tumefaciens with a chimeric tobacco anionic peroxidase (EC 1.11.1.7) gene joined to the cauliflower mosaic virus (CaMV) 35S promoter. Transgenic plants obtained by selection on kanamycin were found to have more than five times the total leaf peroxidase activity of control plants. Transformed tomato plants chronically wilted upon reaching sexual maturity. Two independently selected transformants were self-fertilized, and progeny were obtained that were homozygous for the foreign gene. Isoelectric focusing gels stained for peroxidase activity revealed a new tomato leaf peroxidase isoenzyme with a pI of 3.75, which is similar to that seen in Nicotiana sylvestris L. Mature tomato fruit were found to have up to 1600-fold higher peroxidase activity in transformants expressing the tobacco anionic peroxidase (TobAnPOD) than control plants. Tissue blots showed the tobacco enzyme evenly distributed throughout the tomato fruit tissue. Progeny plants possessing the tobacco peroxidase gene (now homozygous) showed stunting, and fruit size was reduced by >80%. However, fruit set was normal and the rate of ripening was not altered from control plants. Fruit from transformed plants were found to have normal pigmentation, but the soluble solids concentration was 400% higher than in control tomato fruit. This result was predicted from the peroxidase-induced water stress. Possible roles for the tobacco anionic peroxidase in growth, development, and stress resistance are discussed.