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Akira Sugiura, Yoshiko Matsuda-Habu, Mei Gao, Tomoya Esumi, and Ryutaro Tao

In persimmon, plant regeneration from cultured cells usually takes place through adventitious bud formation. If somatic embryogenesis were possible, the efficiency of mass propagation and genetic engineering would be greatly improved. We attempted to induce somatic embryogenesis from immature embryos and plant regeneration from the induced embryos. Hypocotyls and cotyledons from immature ‘Fuyu’ and ‘Jiro’ seeds were cultured in the dark in Murashige and Skoog medium solidified with gellan gum and supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BA) at various concentrations. Callus formation started at ≈2 weeks of culture, and the callus formation rate was highest at 3 or 10 μm combinations of 2,4-D and BA. The initially formed calli gradually became brown or black from which white embryogenic calli (EC) appeared secondarily. After ≈8 weeks of culture, globular embryos were formed from these EC, and the formation proceeded until 20 weeks of culture. Formation of globular embryos was higher with ‘Fuyu’ than ‘Jiro’, especially with hypocotyls. When EC with globular embryos were transferred to fresh medium with no plant growth regulators, ≈70% developed to the torpedo-type embryo stage in 6 weeks. The torpedo-type embryos thus formed were germinated and rooted in agar medium with or without zeatin in several weeks without entering dormancy. After germination and rooting, the plantlets were transferred to the same medium and acclimatized for another 4 weeks. As the embryos germinated and rooted simultaneously, the plantlets were easy to grow in pots without transplanting shock. This is the first report on plant regeneration through somatic embryogenesis of persimmon.

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D. J. Donnelly and W. E. Vidaver

Abstract

The leaf anatomy of an aseptically cultured red raspberry clone (Rubus idaeus L.) was studied before and after transfer to soil under controlled environmental conditions. Leaves of plantlets formed in culture were smaller, thinner, had a less compact arrangement of palisade and mesophyll cells, and an altered palisade cell shape compared to leaves formed on plants in soil. The number of epidermal hairs, especialy the filiform type, was lower in vitro and the distribution of colleters was affected. Trichome number was greater in new leaves formed after transplantation and greatest in greenhouse- and field-grown control plant leaves. Calcium oxalate crystals were present in the leaves of in vitro plantlets and more numerous in the leaves formed on plants in soil. Stomata were fixed open, slightly raised, and occurred on the upper leaf surface of in vitro plantlets with many on the periphery of the leaf. Amphistomatous and the peripheral stomatal condition persisted in new leaves formed during the first month when cultured plantlets were transferred to soil at 3 or 6 klx. However, new leaves, like all greenhouse and field-control plant leaves, had few adaxial stomata at 9 klx and peripheral leaf stomata were rare. Anatomy of new leaves formed during the first month after transplanting in soil at 3, 6, or 9 klx was similar to those in culture. Parenchyma tissue was less compact than in control plant leaves and palisade cell shape remained abnormal. More than half the leaves from culture died within the first month of transferring plantlets to soil. Some survived for almost 3 months. Reduced trichome numbers, almost complete lack of filiform trichomes, and presence of peripheral and adaxial as well as unprotected, open, abaxial stomata would all contribute to transplant shock and water loss in cultured plantlets transferred to soil. New leaves of transplants, formed during the first month in soil, had transitional leaf anatomy and surface features. With time, in the soil environment, the appearance of subsequently formed leaves approached that of controls.

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Jonathan R. Schultheis and Robert J. Dufault

Pretransplant nutritional conditioning (PNC) of transplants during greenhouse production may improve recovery from transplanting stress and enhance earliness and yield of watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai]. Two greenhouse experiments (Expts. 1 and 2) and field experiments in South Carolina and North Carolina (Expt. 3) were conducted to evaluate N and P PNC effects on watermelon seedling growth and their effects on fruit yield and quality. `Queen of Hearts' triploid and `Crimson Sweet' diploid watermelon seedlings were fertilized with N from calcium nitrate at 25, 75, or 225 mg·liter–1 and P from calcium phosphate at 5, 15, or 45 mg·liter–1. In the greenhouse, most variation in the shoot fresh and dry weights, leaf count, leaf area, transplant height, and root dry weight in `Queen of Hearts' and `Crimson Sweet' was attributed to N. Cultivar interacted with N, affecting all seedling growth variables, but not leaf area in Expt. 2. To a lesser extent, in Expt. 1, but not in Expt. 2, P interacted with cultivar, N, or cultivar × N and affected shoot fresh and dry weights, leaf count and leaf area. In the field, transplant shock increased linearly with N, regardless of cultivar or field location. The effect of PNC on plant growth diminished as the growing season progressed. For both cultivars at both locations, N and P PNC did not affect time to first staminate flower, fruit set, fruit width or length, soluble solids concentration, or yield. Vining at Charleston for both cultivars was 2 days earlier when N was at 75 rather than 25 mg·liter–1, without further change with the high N rate. At Clinton, the first pistillate flower was delayed linearly the higher the N rate for `Crimson Sweet'. At Charleston, hollow heart in the `Queen of Hearts' increased nearly 3 times when N PNC rate was tripled (from 75 or 225 mg·liter–1), while N had no effect on hollow heart in `Crimson Sweet'. In contrast, at Clinton, hollow heart in either cultivar was affected by P PNC, not N. PNC with 25N–5P (in mg·liter–1) can be used to reduce seedling growth and produce a more compact plant for easier handling, yet not reduce fruit quality or yield.

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Shinsuke Agehara and Daniel I. Leskovar

field ( Garner and Björkman, 1999 ; Latimer and Mitchell, 1988 ). In addition, the imbalance between transpiration demand and water uptake capacity can result in severe transplant shock and poor stand establishment ( Agehara and Leskovar, 2012

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Christopher J. Biai, José G. Garzon, Jason A. Osborne, Jonathan R. Schultheis, Ronald J. Gehl, and Christopher C. Gunter

acting independently or in combination often limit seedling growth and stand establishment ( Leskovar and Stoffella, 1995 ). Restricted water uptake can lead to sudden and severe plant water deficit, resulting in transplant shock ( Nitzsche et al., 1991

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Tomás Martínez-Trinidad, W. Todd Watson, and Russell K. Book

this research indicate that PBZ in combination with root pruning has a negative impact on tree growth 16 months after treatment. The growth-retarding effect of PBZ after root pruning might reduce transplant shock of newly planted trees or decline of

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Lea Corkidi, Jeff Bohn, and Mike Evans

to transplanting shock ( Azcón-Aguilar and Barea, 1997 ). However, nursery operations are often subjected to regulations that may affect mycorrhizal colonization, such as the use of certain pesticides ( California Department of Food and Agriculture

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Frederic B. Ouedraogo, B. Wade Brorsen, Jon T. Biermacher, and Charles T. Rohla

system to form. However, remediation of a deformed root by pruning may exacerbate transplant shock ( Struve, 1993 ). Another treatment is to remove the potting media. The pH level, soluble salts, and carbon-to-nitrogen ratio contained in the potting mix

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Youping Sun, Genhua Niu, Andrew K. Koeser, Guihong Bi, Victoria Anderson, Krista Jacobsen, Renee Conneway, Sven Verlinden, Ryan Stewart, and Sarah T. Lovell

plant growth and can lead to a condition known as transplant shock ( Koeser et al., 2009 ; McKay, 1996 ). Proponents of plantable biocontainers suggest that their use limits root system disruption and reduces transplant shock ( Evans and Hensley, 2004

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Shinsuke Agehara and Daniel I. Leskovar

, 1998 ). Another drawback was the strong inhibition of root biomass accumulation. Large root systems are important to facilitate pulling of transplants from trays ( Vavrina, 2002 ), whereas insufficient roots can result in severe transplant shock