La variabilidad referente a la precipitación de los últimos 410 años (1599 - 2008) del ciclo invierno-primavera (noviembre-junio) en la parte alta de la cuenca del río Nazas, Durango, México se reconstruyó a partir de la cronología o serie de tiempo desarrollada con base en anillos de crecimiento de Pseudotsuga menziesii, que la explicó en 64%. La reconstrucción para estos cuatro siglos, validada con registros de precipitación y datos de archivos históricos, permitió determinar la presencia de sequías severas entre los periodos 1665 - 1688, 1695 - 1718, 1774 - 1791, 1798 - 1813, 1890 - 1896 y 1945 - 1963. Así, en la correspondiente a este último, de 1948 a 1963, se presentó la más importante del siglo XX; así como de, esos 410 años, por su impacto en la sociedad y la economía; sin embargo, aquellas de 1665 - 1688 y 1695 - 1718, pudieron haber causado efectos similares por su intensidad. En la parte alta de la cuenca, la precipitación es modulada de manera significativa (p<0.05) por El Niño Oscilación del Sur (ENSO, por sus siglas en inglés) tanto en su fase fría (La Niña), al producir intensa escasez de agua con repercusiones económicas, políticas y sociales para los pobladores de la Comarca Lagunera, como en su fase cálida (El Niño), con importantes incrementos en la pluviometría de la región.
En la Sierra de Arteaga del estado de Coahuila, México, se generaron cinco cronologías de madera temprana, madera tardía y anillo total de Pseudotsuga menziesii para las montañas La Viga, El Coahuilón, El Tarillal, Los Pilares y El Morro. Un Análisis de Componentes Principales (PCA) indicó que las cinco cronologías presentan una variabilidad común (p<0.001); el componente uno (PC1) explica 72% de la variabilidad, sin embargo, se eliminó la cronología El Morro por tener la más baja correlación. Con las cronologías restantes se desarrolló una regional de 302 años de extensión (1700 a 2001). Mediante un análisis de Función de Respuesta se definió que los crecimientos de madera temprana y tardía responden a la precipitación invierno-primavera. Debido a que la madera tardía explica 50% de la variabilidad en precipitación, se optó por trabajar con la madera temprana para reconstruir la precipitación, que determina 75% de su variabilidad. La reconstrucción señala etapas secas severas para los períodos 1785-1815, 1853-1882, 1951- 1963 y 1970-1985. De igual manera, para los intervalos 1737-1747, 1824-1852 y 1935-1948 se detectó alta precipitación. En general, se observan periódicas cada inicio o finales de siglo (1700, 1800, 1900 y 2000) y cada mitad de siglo (1750, 1850 y 1950). Mediante un análisis de Coherencia de Ondeleta Cruzada se concluyó que el fenómeno de El Niño Oscilación del Sur (ENSO) ha influido de manera significativa (p<0.001) en la variabilidad climática de la región, particularmente para los períodos 1905- 1930 y 1974- 1988.
In this study, the aim was to develop the compositional nutrient diagnosis (CND) norms for Opuntia ficus indica variety 'Rojo Pelón’ fruiting. Statistical analyses involved a dataset of fruit yield and macro-nutrient concentrations of 228 1-year old cladodes from healthy plants. A cutoff yield (1,166.67 g cladode-1) between the low- and high-yield subpopulations was determined after examining six cumulative variance ratio functions related to yield per 1-year old cladode. Means and standard deviations of row-centered log-ratios of five nutrients (N, P, K, Ca, and Mg) and a filling value Rd, which includes all nutrients not chemically analyzed. Estimated preliminary CND norms (mean ± standard deviation of the row-centered log-ratios) are: = ?1.114 ± 0.219, = ?2.194 ±0.076, = 0.163 ± 0.259, = ?0.708 ± 0.157, = 0.401 ± 0.100, and = 3.452 ± 0.095. These CND standards are associated with the following 1-year old fruiting cladode mean concentrations: N=0.958%, P=0.318%, K=3.507%, Ca=4.228%, and Mg=1.448%. Then, the order of macro-nutrient requirements is as follows: Ca>K>Mg>N>P.
Since 2001, 15 to18% of commercial plantings of the medicinal plant St. John's-wort (Hypericum perforatum L.) in Buenos Aires Province, Argentina were affected by a new disease. Disease symptoms of crown and root rot, wilting, chlorosis, and necrosis of the leaves appeared in circular-to-irregular shaped sectors of 12- to 14-month-old plants. Symptoms began with foliage turning yellow followed by an irregular, brown necrosis of the leaf margins. Lesions coalesced to form large necrotic areas causing a severe defoliation of the basal and upper leaves. A soft rot affected the crown and roots causing a complete maceration of these tissues. Infected plants broke off easily because the crown region and the roots were destroyed. As the disease developed, a dark brown discoloration girdled the stems that progressed above the soil line to the apex. The infected stems became dry and breakable. Finally, the affected plants died. Segments (1 cm long) were taken from roots and rotted crowns of diseased plants, dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 1 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar. Plates were incubated in the dark at 26°C for 4 to 7 days. The predominate fungus isolated from the diseased tissue was identified as Fusarium solani (Mart.) Sacc. (1). Koch's postulates were completed by dipping the roots of seedlings in a 2 × 106 conidia per ml suspension of a single spore isolate for 45 min. Plants were repotted (20 inoculated and 10 controls) in a sterilized soil mix (soil/sand 2:1) and held in the greenhouse at 23 to 26°C. Characteristic symptoms identical to the original developed on 90% of inoculated plants within 2 weeks after inoculation. Symptoms included wilt and collapse, crown and root rot, and death of the plants. The fungus was recovered from symptomatic tissues. Control plants dipped into distilled water remained healthy. The experiment was repeated, and the results were identical to the first inoculations. To our knowledge, this is the first report of St. John's-wort as a susceptible host of F. solani. Reference: (1) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.
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