The instability of in vitro cultures may cause genetic and epigenetic changes in crops called somaclonal variations. Sometimes, these changes produce beneficial effects; for example, they can be used in breeding programs to generate new cultivars with desirable characteristics. In this article, we present a systematic review designed to answer the following question: How does somaclonal variation contribute to plant genetic improvement? Five electronic databases were searched for articles based on pre-established inclusion and exclusion criteria and with a standardized search string. The somaclonal variation technique has been most frequently applied to ornamental plants, with 49 species cited in 48 articles, and to the main agricultural crops, including sugarcane, rice, banana, potato and wheat, in different countries worldwide. In 69 studies, a technique was applied to evaluate the genetic diversity generated between clones, and, in 63 studies, agronomic performance characteristics were evaluated. Other studies are related to resistance to pathogens, ornamental characteristics and resistance to abiotic stresses. The application of the plant growth regulators (PGRs) benzylaminopurine (BAP) and dichlorophenoxyacetic acid (2,4-D) was the most common method for generating somaclones, and randomly amplified polymorphic DNA (RAPD) molecular markers were the most commonly used markers for identification and characterization. Somaclonal variation has been used in genetic improvement programs for the most economically important crops in the world, generating genetic diversity and supporting the launch of new genotypes resistant to diseases, pests and abiotic stresses. However, much remains to be explored, such as the genetic and epigenetic mechanisms from which somaclonal variation is derived.
El objetivo del estudio fue comparar 2 disoluciones extractoras de boro (fosfato de calcio y Mehlich 3), y determinar su contenido en el suelo y en la planta de banano (tercera hoja). El trabajo se efectuó en el Laboratorio Químico de CORBANA S.A., ubicado en la provincia de Limón, cantón de Pococí, distrito La Rita, en el 2015. Para tal propósito se colectaron muestras de suelo y de tejido foliar provenientes de plantaciones bananeras situadas en el Caribe costarricense. Suelos con contenidos inferiores a 0,2 mg.l-1 de boro presentaron una mayor extracción del elemento con la disolución Mehlich 3, en comparación con la disolución de fosfato de calcio. Contenidos entre 0,2 y 0,7 mg.l-1 mostraron, por su parte, una correlación del 68% entre ambas disoluciones. Niveles superiores a 2 mg.l-1 exhibieron una correlación del 98%. El noventa por ciento de las muestras de suelo analizadas presentaron contenidos de boro menores a 1,0 mg.l-1, con la mayoría de las muestras (64%) en concentraciones de 0,2 a 0,7 mg.l-1. El ámbito de boro recomendado para la planta de banano es de 0,1 a 1,0 mg.l-1, por lo que la mayoría de los suelos muestreados presentaron valores adecuados. Las concentraciones foliares de boro fueron de 10 a 15 mg.kg-1 en la sección central interna de la tercera hoja, mientras que en la sección externa de la hoja (borde) fueron de 10 a 70 mg.kg-1 con un aumento de su concentración hacia el borde de la hoja. Los resultados indican la bondad del uso de la disolución de Mehlich 3 sobre la disolución de fosfato de calcio para la determinación de boro en muestras de suelo.
The full cycle from embryogenic callus (EC) induction to field evaluation of regenerated plants is reported for the first time for banana cv. "Datil" (Musa AA). Immature male flowers were used for EC induction on a modified M1 culture medium. The ideal type of EC was obtained in the presence of 4.5 M and 9.0 M 2,4-dichlorophenoxyacetic acid (2,4-D). Embryogenic cell suspensions were established in both concentrations of 2,4-D; however, only the suspensions from ideal callus (IC) formed with 4.5 µM of 2,4-D were regenerated. A histological study revealed the formation of structurally different cell masses during the regeneration phase of cv. "Datil". The embryos germination was characterized by the growth cellular aggregates, indicating the possible occurrence of secondary embryogenesis. Development and acclimatization of the plants were carried out in a normal manner as observed for other cultivars. Field evaluation of the plants' genetic stability was based on observation of morphological traits. In the vegetative growth phase, 6.61% of the plants presented drooping leaves and deformed semi-limbs. These traits, however, did not affect further plant growth during flowering and harvest phases. The produced fruits were of good quality. And the present study indicates that this cultivar may be stable genetically.
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