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Worldwide, potato (Solanum tuberosum L.) crops cover 18×10 6 ha, corresponding to a production of 314× 10 6 t. The importance of this crop makes it crucial to control production losses and quality defects due to foliar injury, whether by natural or mechanical causes. The artificial defoliation of potatoes is a common technique used to investigate the correlation between damage caused by either hail or insects and yield. The aim of this study was to evaluate simulated hail damage on different cultivar potatoes of varying maturity to quantify the commercial yield reduction attributable to different defoliation levels through the potato crop cycle. Eight trials were carried out in the Central Ebro Valley (northern Spain) over a period of 4 years with three potato cultivars: Jaerla, Red-Pontiac, and Baraka. Four levels of defoliation (no defoliation, slight defoliation, medium defoliation, and high defoliation) were carried out in several phenological stages. The crop yield losses for each level of defoliation were calculated by correlating the percentage of defoliation applied and the resulting percentage of yield loss. Yield reduction equations were calculated for each trial and phenological stage. Damaged produced during tuber formation or flowering considerably reduced yield. In contrast, defoliations after tubers had completed growth barely affected yields. Differences among cultivars with respect to yield losses were noted regardless of location and year. The early cultivar (Jaerla) recovered worse than the longer-cycle varieties (Red Pontiac and Baraka) as concerns defoliation effects. Effects on yield were similar at the different locations. The regression equations presented may be used for modeling the yield reduction due to defoliation treatments caused by different biotic and abiotic agents.Resumen En todo el mundo, los cultivos de papa (Solanum tuberosum L.) cubren 18×10 6 ha, lo que corresponde a una producción de 314×10 6 t. La importancia de este cultivo hace crucial el control de las pérdidas de producción y de los defectos en calidad debido al daño foliar, ya fuera por causas naturales o mecánicas. La defoliación artificial de papa es una técnica común usada para investigar la correlación entre el daño causado por granizo o insectos y rendimiento. El propósito de este estudio fue evaluar el daño simulado por granizo en diferentes variedades de papa de diversa madurez, para cuantificar la reducción comercial en rendimiento atribuible a diferentes niveles de defoliación a lo largo del ciclo de cultivo de la papa. Se hicieron ocho ensayos en el valle central del Ebro (al norte de España) en un período de cuatro años con tres variedades de papa: Jaerla, Red-Pontiac, y Baraka. Se efectuaron cuatro niveles de defoliación (sin defoliación, ligera, media, y alta defoliación) en varios estados fenológicos. Se calcularon las pérdidas en el rendimiento del cultivo para cada nivel de defoliación, mediante la correlación del porcentaje de defoliación aplicado y el porcentaje resultante de pérdida en el rendimien...

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The sweetener compounds in Stevia, steviol glycosides (SG), are mainly found in the leaves. The SG content depends on the plant's growth stage and is usually highest just before flowering. In temperate areas, Stevia is a polyannual crop (5 -7 years) with a vegetative period lasting from April-May until October, during which time the crop can be harvested two or three times. This research focuses on the need for knowledge about Stevia's response to temperate climates in Southern Europe. Two field assays were established from June to October 2013 at two sites in Navarra (Spain). The biomass and content of the two major SG, stevioside (ST) and rebaudioside A (RA), were measured using High Performance Liquid Chromatography (HPLC) in 66 cloned plants, at different developmental stages. Although the results from the two sites showed different SG leaf content dynamics during the plant growth, the optimum harvest date at both sites coincided with the bud-flowering stage at the beginning of September (around 96 days after planting), when a ST yield of 27 g·m −2 was reached. These results show Stevia's potential as a commercial crop for stevioside production in northern Spain.

Morphological and physiological responses of plants to stress determine the effects on the final production (Prins and Verkaar, 1992). Simulation models of crop development and growth should take into account these processes in order to simulate correctly the damage suffered and the impact on the yield.The foliar area loss is a typical damage in crops caused by fungus, insect attacks or hailstorm and several studies have been done to describe defoliation effects on the main herbaceous and woody crops such as Vitis AbstractThe foliar area loss is a typical damage in crops caused by fungus, insects or hailstorm. A lot of studies have been carried out to describe the effect of defoliation in the main herbaceous and woody crops. The results of two trials carried out in Valle Medio of the Ebro (Spain) are described in this study to determine the effects of different levels of defoliation in several phenological stages in leek crop. Four levels of defoliation were applied: control, slight, moderate and heavy, in six different phenological stages. Defoliations were carried out by means of a jet of water under pressure. According to the results observed, a close relationship between the yield loss with the percentage of defoliation and the crop stage was found. The most critical stage was at the beginning of the stem thickening in which there are maximum losses of 41% with 100% of defoliation. These experimental results were used to obtain regression equations in which the percentage of yield reduction is calculated in relation with the phenological stage and the percentage of defoliation. These equations can be used to improve simulation patterns of the leek growth in case of foliar damages caused by fungus, insect attacks or hailstorm.Additional key words: foliar damage, hail, simulation, yield loss. ResumenEfecto de la defoliación en el cultivo de puerro (Allium porrum L.)La pérdida de área foliar es un daño típico en los cultivos causado por ataques de hongos e insectos o por granizo. Se han realizado numerosos estudios para describir los efectos de la defoliación en los principales cultivos herbáce-os y leñosos. En este trabajo se describen los resultados obtenidos en dos ensayos, llevados a cabo en el Valle Medio del Ebro (España), para determinar el efecto en el cultivo de puerro de diferentes niveles de defoliación aplicados en varios estados fenológicos. Se aplicaron cuatro niveles de defoliación: control, leve, medio y alto en seis estados fenológicos diferentes. La defoliación se llevó a cabo con una maquina de agua a presión. Se observó una estrecha relación entre la pérdida de cosecha, el porcentaje de defoliación y el estado fenológico en que se aplicó. El estado más crítico fue al inicio del engrosamiento del tallo en el cual se alcanzaron las mayores pérdidas, de un 41% para un 100% de defoliación. Estos resultados experimentales se utilizaron para obtener ecuaciones de regresión en las que se calculó el porcentaje de pérdida de cosecha en relación con el estado fenológico y el porcentaje de defoliación...

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