Browsing by Author "Guardiola, J. L."
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- Aplicaciones del calcio en citriculturaPublication . Duarte, Amílcar; Guardiola, J. L.La esencialidad del calcio para las plantas se estableció de modo inequívoco hace más de cien años, incluyéndose ya como componente en las primeras soluciones nutritivas que se desarrollaron.Lav presencia de calcio en la solución nutritiva se demotró necesaria para el crecimiento de la raíz, que en su ausencia se detiene en el plazo de unas poucas horas.
- El rajado estilar del fruto en los citricos: aspectos anatomicos y morfologicosPublication . García-Luis, A.; Kanduser, Masa; Duarte, Amílcar; Guardiola, J. L.El rajado o agrietado es una alteración del fruto, y aun de otras partes utilizables de la planta, que se caracteriza por la formación de fisuras profundas en la piel o corteza de tal modo que la parte interna comestible del fruto queda expuesta y aun se agrieta. El fruto afectado en muchos casos se desprende prematuramente, pero aun en el caso de que complete su desarrollo y alcance la maduración es inservible para la comercialización. Esta alteración se ha descrito en gran número de especies, entre las que se encuentran frutales de hueso y de pepita, plantas hortícolas (como el tomate) y los cítricos, provocando a menudo pérdidas económicas importantes. Las características de la misma han sido revisadas de modo crítico recientemente por Opara y col. (1997), que resaltan los aspectos siguientes: a) Existe un factor genético en la predisposición a la presencia de esta alteración, mucho más frecuente en algunos cultivares de cada una de las especies; b) Hay una variación marcada en la susceptibilidad a la misma entre árboles y entre frutos de un mismo árbol; c) La alteración es afectada por factores ambientales, de tal modo que su incidencia varía notablemente de un año a otro y entre parcelas de la misma especie; d) No hay un factor causal único de la alteración, y e) Las prácticas correctivas desarrolladas son de resultado errático, variando su eficacia de modo marcado sin que sea posible establecer una pauta de respuesta definida. La influencia de estos factores en la incidencia del rajado en los cítricos son evidentes. La alteración es frecuente en los cultivares Nova, Murcott y Ellendale, mientras se presenta raramente en satsumas y clementinas. Para una misma variedad el porcentaje de rajado varía notablemente entre parcelas y, en una misma parcela, de un año a otro, siendo en general más elevado en regiones cálidas y húmedas, factores climáticos que favorecen la formación de frutos de piel fina (Alexander, 1983; Robe and Van Rensburg, 1996). Probablemente las diferencias climáticas son responsables del comportamiento diferente de algunas variedades en distintas regiones citrícolas, como ocurre con las variedades del tipo navel, que en Florida presentan un porcentaje significativo de frutos rajados mientras en las condiciones de Valencia el rajado del fruto no tiene normalmente importancia, así como de las diferencias en comportamiento en una misma región en años diferentes. Es notable al respecto que el tangor Ortanique, que en las condiciones de Valencia normalmente no se raja, ha presentado este año en algunas parcelas un porcentaje de rajado superior al 40%.
- Factors affecting rind pitting in the mandarin hybrids "fortune" and "nova". The influence of exogenous growth regulatorsPublication . Duarte, Amílcar; Guardiola, J. L.The commercialization of the mandarin hybrids "Fortune" and "Nova" is hindered by the development of cold-induced pitting in the fruit rind which may develop either in the orchard or during storage and transport. In the late cropping cultivar "Fortune", the pitting develops on tree during the winter months and affects mainly the exposed fruit from the north-west quadrant of the tree. The induction of symptoms under uniform conditions in the cold-room reveals differences in the susceptibility to chilling injury among the fruits and the fruit sides. The green fruit is not susceptible. Susceptibility develops as pigmentation progresses, and it is higher for the exposed than for the non-exposed (covered by the foliage) fruits. The application of GA3 at colour-break delays pigmentation and retards the development of susceptibility. The waxing of the fruit offers some protection to cold in the cold-room. However, the incidence of pitting is not related to the wax content of the fruit rind and the application of a wax coverage on tree had only a marginal protective effect. No pitting is usually found on tree in the fruit of the early ripening "Nova" cultivar, which is usually harvested before the winter chilling. The pitting develops during cold storage (8-10 C), and is reduced by GA3 application at colour break, an effect related to the delay in rind pigmentation.
- Flowering and fruit set of 'fortune' hybrid mandarin. Effect of girdling and growth regulatorsPublication . Duarte, Amílcar; Guardiola, J. L.Young orchards of 'Fortune' mandarin usually have a low productivity due to insufficient fruit set. The trees flower profusely, and most of the flowers are borne on leafless inflorescences. Leafy inflorescences are formed in a very low proportion and vegetative sprouts are nearly absent. This sprouting pattern results in a very low leaf/flower ratio. The carbohydrate reserves of the trees are lower than reported for other citrus cultivars, and are depleted shortly after anthesis. Therefore, the growth of the developing fruitlets depends mostly on current photosyntate formation. Most of the ovaries abscise shortly after flowering, having made very little growth. There is a main peak of abscission from early May until the end of June. Late fruitlet abscission lasts until late July. A GA3 spray at flowering retarded the abscission of reproductive organs, but failed to increase the final fruit set. On the other hand girdling did not affect the main wave of drop, but reduced late abscission, which resulted in an increase in set and final yield. Girdling did not increase the level of carbohydrates in the leaves, which indicates that carbohydrate use is determined by availability and fruit set may be limited by photosynthate supply.
- Thinning of ‘Esbal’ clementine with 2,4-dichlorophenoxyacetic acid. Influence on yield, fruit size and fruit quality.Publication . Duarte, Amílcar; Trindade, D. T. G.; Guardiola, J. L.Esbal clementine, which originated as a bud sport from ‘Fina’, is a high parthenocarpyc early maturing cultivar with outstanding fruit quality. The expansion of this cultivar is nevertheless impaired by the small fruit size, as up to 40% of the total yield may be unmarketable due to this reason. Extensive hand thinning and auxin applications at June drop have been tried to overcome this problem with limited success. The application of a 2,4-D spray at or shortly after bloom thins effectively the number of fruits without affecting total yield, reducing the percentage of unmarketable fruit down to 13% and increasing the mean size of the marketable fruit. This thinning effect is not related to an auxin-induced ethylene synthesis, but results from the selective enhancement of the growth of some fruits by the 2,4-D application. The 2,4-D applications had no direct effect on sugar and acid content of the fruit nor in the maturity index, but the increase in fruit size resulted in an earlier maturity. This applications resulted in a reduction in juice content, but this reduction was smaller than observed when auxins were applied at june drop.
- Utilización de reservas en fructificación en el mandarino "Fortune". Influencia de las técnicas de cuajadoPublication . Duarte, Amílcar; Guardiola, J. L.The utilization of reserves in fruiting in the "Fortune" mandarin. The influence of fruit set techniques.The effects on fruit set of GA3, BA, and NAA applications, and that of girdling, has been determined in relation to the mobilization of the reserves during flowring and June drop.Under the conditions of this experiment, performed with high flowering trees, carbohydrate and nitrogen contents in the leaves during flowering and fruitlet abscision were lower than the content found in other cultivars. We could not establish a relationship between metabolite availability and fruit set. Girdling was the only effective fruit set treatment. It had no effect on the carbohydrate and the total nitrogen contents in the leaves, and reduced the amino nitrogen content.