North American oak species, with their characteristic strong episodic seasonal shoot growth, are highly problematic for clonal micropropagation, resulting in the inability to achieve a stabilized shoot multiplication stage. The potential for initiating and proliferating shoot cultures derived from Quercus alba, Q. bicolor and Q. rubra explants was investigated, and a micropropagation method for these species was developed. Branch segments from 6 to 7-year-old trees were forced-flushed and the forced shoots were used as source of explants for culture initiation. A consistent shoot multiplication stage was achieved, in 13 of the 15 genotypes established in vitro, although marked differences occurred in explants from different genotypes/species. The control of efficient shoot multiplication involved the culture of decapitated shoots in a stressful horizontal position on cytokinin-containing medium with a sequence of transfers within a 6-week subculture cycle, which was beneficial to overcoming the episodic character of shoot growth. During each subculture cycle, the horizontally placed explants were cultured on media containing 0.2 mg l -1 benzyladenine (BA) for 2 weeks with two successive transfers (2 weeks each) to fresh medium with 0.1 mg l -1 BA, giving a 6-week subculture cycle. The general appearance and vigor of Q. alba and Q. bicolor shoot cultures were improved by the inclusion of both 0.1 mg l -1 BA and 0.5 mg l -1 zeatin in the medium used for the second transfer within the 6-week subculture cycle. Addition of AgNO 3 (3 mg l -1 ) to the shoot proliferation medium of Q. rubra had a significant positive effect on shoot development pattern by reducing deleterious symptoms, including shoot tip necrosis and early senescence of leaves. The three species showed acceptable in vitro rooting rates by culturing microcuttings in medium containing 25 mg l -1 indolebutyric acid for 48 h with subsequent transfer to auxin-free medium supplemented with 0.4% activated charcoal. Although an initial 5-day dark period generally improved the rooting response, it was detrimental to the quality of regenerated plantlets. However, activated charcoal stimulated not only the rooting frequencies, but it also enhanced plant quality, as evidenced by root, shoot and leaf growth.
A reproducible procedure for induction of somatic embryogenesis (SE) from adult trees of Eucalyptus globulus Labill. and the hybrid E. saligna Smith × E. maidenii has been developed for the first time. Somatic embryos were obtained from both shoot apex and leaf explants of all three genotypes evaluated, although embryogenic frequencies were significantly influenced by the species/genotype, auxin and explant type. Picloram was more efficient for somatic embryo induction than naphthaleneacetic acid (NAA), with the highest frequency of induction being obtained in Murashige and Skoog medium containing 40 µM picloram and 40 mg l(-1) gum Arabic, in which 64% of the shoot apex explants and 68.8% of the leaf explants yielded somatic embryos. The embryogenic response of the hybrid was higher than that of the E. globulus, especially when NAA was used. The cultures initiated on picloram-containing medium consisted of nodular embryogenic structures surrounded by a mucilaginous coating layer that emerged from a watery callus developed from the initial explants. Cotyledonary somatic embryos were differentiated after subculture of these nodular embryogenic structures on a medium lacking plant growth regulators. Histological analysis confirmed the bipolar organization of the somatic embryos, with shoot and root meristems and closed procambial tissue that bifurcated into small cotyledons. The root pole was more differentiated than the shoot pole, which appeared to be formed by a few meristematic layers. Maintenance of the embryogenic lines by secondary SE was attained by subculturing individual cotyledonary embryos or small clusters of globular and torpedo embryos on medium with 16.11 µM NAA at 4- to 5-week intervals. Somatic embryos converted into plantlets after being transferred to liquid germination medium although plant regeneration remained poor.
El Instituto Nacional de Semillas (INASE) de Uruguay otorga los títulos de propiedad para los nuevos cultivares, siguiendo las directrices de la Unión Internacional para la Protección de las Obtenciones Vegetales (UPOV). Un cultivar puede ser protegido si cumple con los requisitos de ser diferente, homogéneo y estable (DHE). El objetivo de este estudio fue determinar si 13 cultivares de Solanum tuberosum L. cumplen con el requisito de ser DHE, necesario para ser protegidos. Los ensayos fueron realizados en los otoños de 2008 y 2009 en San José, Uruguay. La unidad experimental fue de parcelas de 30 plantas. Los cultivares candidatos a ser protegidos fueron: ‘Apolline’, ‘Camberra’, ‘Colorado Rose’, ‘CP 97145.2’ (INIA Yaguarí), ‘Daifla’, ‘INIA Iporá’, ‘Kenita’, ‘Mountain Rose’, ‘Mozart’, ‘Purple Majesty’, ‘Red Magic’, ‘Sagita’ y ‘Voyager’. Se incluyeron cinco cultivares de uso público: ‘Atlantic’, ‘Cal White’, ‘Chieftain’ ‘Dark Red Norland’ y Romera’. Se estudiaron 32 características morfo-fenológicas de planta, tallo, hoja, folíolo, brote y tubérculo. Las características de los tubérculos cosechados se analizaron en laboratorio y cámara de brotación. Se realizó la descripción varietal de cada cultivar. Las características que mejor diferenciaron a los cultivares fueron: forma de tubérculo, color de pulpa (blancas, amarillas, rojas y violeta) y color de piel (amarillas, rojas y violeta). Los resultados indicaron que los cultivares candidatos a ser protegidos fueron diferentes a los notoriamente conocidos, presentaron homogeneidad y se mantuvieron estables. Por lo tanto, los 13 cultivares estudiados cumplen con los requisitos de DHE establecidos para la obtención del título de propiedad.
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