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Jane Kahia, Margaret Kirika, Hudson Lubabali and Sinclair Mantell

Breeding work carried out during the period 1971–85 by the Coffee Research Institute, Ruiru, Kenya resulted in the release of a new improved hybrid Coffea arabica named Ruiru 11. The cultivar combines resistance to coffee berry disease (CBD) and leaf rust, with high yield and good cup quality attributes. The propagation by F1 hybrid seeds production, cuttings, and tip grafting do not produce enough planting materials. There was a need to explore alternative methods and tissue culture offers potential options. The objective of the study was to evaluate the effect of explant sources and cytokinins on induction and regeneration of somatic embryos. Eight different explants were cultured on half-strength Murashige and Skoog (MS) medium supplemented with 10 µm benzylaminopurine (BAP). The effect of kinetin, N6-(2-isopentyl) adenine (2iP) evaluated at (0, 0.5, 5, or 25 µm) or thidiazuron (TDZ) (0, 0.5, 1.0, or 5 µm) added in separate experiments was also evaluated. The percentage of embryogenic cultures and the numbers of embryos per explant were determined after 3 months’ culture. The explant type had a significant effect (P > 0.05) on the induction of somatic embryos. Explants from in vitro-germinated seedlings produced the highest embryogenic cultures (90%) and the highest mean number of embryos (19.36) per explant. Cytokinins strongly enhanced induction and regeneration of somatic embryos. TDZ at 1 µm produced the highest embryogenic cultures (100%) and the highest mean number of embryos (24.2). The embryos were germinated on half-strength MS medium without any hormones. A high (98%) survival rate of the regenerated plantlets was recorded over all the treatments in the greenhouse. This is the first report on induction of high-frequency direct somatic embryos from coffee juvenile tissues. This is of great significance in tissue culture and indeed molecular biology manipulations because it allows regeneration of coffee from several explants.

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Aekaterini N. Martini, Maria Papafotiou and Stavros N. Vemmos

different degree of maturity of different parts of mature trees. Using explants from juvenile tissues, which are often at the basal parts of mature trees, in vitro propagation can be achieved. Explants taken from juvenile parts (epicormic shoots, lower

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John L. Maas, Gene J. Galletta and Barbara J. Smith

We have determined in tests conducted both at Beltsville and Poplarville that several strawberry isolates of Colletotrichum acutatum, C. gloeosporioides and C. fragariae produce toxin-like compounds in culture. Crude culture filtrates (CFI elicited general and specific responses in tomato and strawberry plants. Tomato plants initially were used because they are highly responsive to toxins in general, whereas the reaction of strawberry plants apparently is greatly affected by environmental and nutritional growing conditions of the test plant. Toxin symptoms included leaf chlorosis and wilting, leaf midvein darkening, and plant death when CF was applied to leaves or if seedlings or petioles were immersed into CF. Juvenile tissues appear to be more susceptible to the effects of the toxins than mature tissue. No differences in response to culture filtrates were apparent among those from the Colletotrichum isolates. The putative toxins appear to act differentially with susceptible or resistant strawberry germplasm.

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Laurie E. Boyden and Peter S. Cousins

Breeders of woody perennials seek to shorten the time from propagation to flowering and the turnover time between generations. Grapevines usually flower and fruit no earlier than their third season. Onset of flowering occurs when anlagen, undifferentiated primordia arising from axillary and terminal bud meristems, begin to develop into inflorescences as well as tendrils. This occurs in response to hormonal stimuli; high levels of gibberellins in juvenile tissue favor vegetative growth, whereas increased cytokinin levels in physiologically mature tissue favor reproductive growth. We modified a method developed for Vitis vinifera for use on grape rootstock seedlings. Exogenous applications of chlormequat and N-benzyl-9-(2-tetrahydropyranyl) adenine (PBA, a cytokinin) were used induce precocious flowering by increasing the cytokinin:gibberellin ratio, triggering anlagen to develop into inflorescences on physiologically juvenile vines. The optimum treatment was a single application of 3000 micromolar chlormequat and 250 micromolar PBA, followed by 10 subsequent daily applications of PBA alone. Lower concentrations of treatments resulted in a loss of efficacy, and higher treatment concentrations and/or longer durations resulted in phytotoxicity. Abnormalities in flower and leaf morphology were observed with all treatments. Grape rootstock seedlings are dioecious and staminate vines were more responsive to the treatments than pistillate vines. We did not observe production of hermaphroditic flowers on staminate vines. Pollen collected from flowering staminate seedlings was successfully used in crosses that produced fruit and viable seeds. The ability to induce precocious flowering in juvenile grape seedlings has many applications in grape breeding and genetic research.

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M.L. Marin and N. Duran-Vila

A study was conducted to evaluate the potential of in vitro techniques for genetic conservation of citrus. A tissue culture system was developed using explants of juvenile `Pineapple' sweet orange. It consisted of: a) establishment of primary cultures from nodal stem segments followed by the recovery of plants in vitro; and b) successive cycles of secondary cultures consisting of the culture of nodal stem segments from in vitro-grown plants, rooting of shoots obtained from nodal stem segments, and recovery of whole plantlets. Two parameters, K and K', based on the multiplication factors of the different stages of primary and secondary cultures are proposed to monitor the system as a potential tool for genetic conservation of citrus. The system also can be successfully used for the conservation of juvenile tissues of two sweet orange varieties [Citrus sinensis (L.) Osb.], trifoliate orange [Poncirus trifoliata (L.) Raf.], Mexican lime [C. aurantifolia (Christm.) Swing.], and `Eureka' lemon [C. limon (L.) Burro. f.]. Chemical names used: 6-benzylaminopurine (BA); α- naphtbaleneacetic acid (NAA).

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Madhurababu Kunta, John V. da Graça, Nasir S.A. Malik, Eliezer S. Louzada and Mamoudou Sétamou

titers were recorded for grapefruit compared with sweet orange ( F = 17.49; df = 1, 30, P = 0.0002) and juvenile tissues (not sampled from sweet orange), no significant differences were observed for other plant parts between the two host plants

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Masafumi Johkan, Genjirou Mori, Kazuhiko Mitsukuri, Keiichirou Mishiba, Toshinobu Morikawa and Masayuki Oda

, differentiation generally occurs more readily in juvenile tissue than in mature tissue in vitro ( De Donato et al., 1989 ), and tissue browning is frequently observed in callus cultures derived from mature explants in some of the higher plant species ( Tang et al

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Yuyu Wang, Faju Chen, Yubing Wang, Xiaoling Li and Hongwei Liang

juvenile tissues seemed more suitable. Other results indicated that zygotic embryos of cashew nut ( Anacardium occidentale L.) at different developmental stages showed different potential for somatic embryogenesis ( Gogate and Nadgauda, 2003 ). In further

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Oscar García-Rubio and Guadalupe Malda-Barrera

; Ramirez-Malagon et al., 2007 ), where growth regulator complementation, especially cytokinins, is crucial for shoot generation. These findings suggest that endogenous levels of growth regulators present in M. mathildae juvenile tissues are sufficient

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Ajay Nair, Donglin Zhang, John Smagula and Dongyan Hu

spring. Rooting hormone. Adventitious rooting is determined and controlled by a number of factors like environment (light, temperature, and oxygen), nutrition (carbohydrates, water, macro-, and microelements), and plant health (juvenility, tissue