Resumo Espécies de citros cultivadas em zonas temperadas têm brotação inibida no inverno, retornando na primavera quando elas também florescem. O principal fator que define o destino vegetativo ou reprodutivo das gemas é a presença de frutos em desenvolvimento. Baixas temperaturas no inverno retardam o metabolismo das plantas, que tem sido relatado como necessário para o desenvolvimento do sistema reprodutivo. Durante o ciclo anual, no período de inverno, compostos osmoticamente ativos como a prolina são aumentados como parte da resposta de tolerância ao frio. Foi investigado se a presença de frutos em desenvolvimento e a aplicação de giberelinas exógenas afetam o nível de prolina em folhas cítricas. Em um pomar de tangerina ‘Montenegrina’ adulta, o conteúdo de prolina foliar foi medido em dois períodos de descanso para ramos com ou sem frutos. Os ramos que floresciam, aqueles que não tinham frutos em desenvolvimento, apresentaram níveis mais elevados de prolina, bem como maiores proporções de prolina: clorofila e prolina: aminoácidos totais do que os ramos com frutos. No entanto, a aplicação de giberelinas exógenas, que reduziram a floração, não afetaram o conteúdo de prolina durante os mesmos períodos. Discutimos as maneiras pelas quais a prolina pode estar envolvida na indução floral dos citros.

Abstract Citrus species grown in temperate zones have sprouting inhibited in winter and this is retaken in spring when they also bloom. The main factor that defines the vegetative or reproductive destiny of the buds is the presence of fruits in development. Low winter temperatures slow plant metabolism, which has been reported as necessary for the expression of the reproductive program. During the winter period of the annual cycle, osmotically active compounds such as proline are increased as part of the cold tolerance response. We investigated whether the presence of developing fruit and the application of exogenous gibberellins affect the proline level in citrus leaves. In an orchard of adult ‘Montenegrina’ mandarin trees, leaf proline contents were measured over two rest periods for branches with or without fruits. Branches that bloomed, the ones that did not have developing fruits, had higher proline levels as well as higher proline: chlorophyll and proline: total amino acid ratios than did branches with fruits. However, the application of exogenous gibberellins, which reduced flowering, did not affect proline content during the same periods. We discuss the ways in which proline may be involved in floral induction in citrus.

El uso de productos compensadores de frío en manzana (Malus domestica) es una técnica ampliamente difundida en Uruguay. Este trabajo evaluó la respuesta a la aplicación de compensadores en dos variedades (Red Chief y Granny Smith), en tres momentos de aplicación (MA) en 2005 y 2006. Los compensadores fueron evaluados en un experimento factorial con dos factores, producto y momento. Los productos aplicados fueron cianamida hidrogenada (H2CN2) al 2,5%, aceite mineral parafínico al 3%, aceite mineral parafínico refinado al 2%, y una combinación de H2CN2 al 0,75% + aceite mineral parafínico al 2%. La primera aplicación fue realizada cuando se alcanzaron 250 UF (modelo UTAH) (primera quincena agosto), las siguientes, la primera y tercera semana de setiembre. El inicio de salida de endodormancia se fijó cuando se alcanzó el 50% de la caída de hojas y su finalización fue definida cuando se alcanzó el 50% de yemas brotadas en brindillas en cámara de crecimiento controlado. Semanalmente se evaluó el porcentaje de brotación en condiciones de campo, se cuantificó el crecimiento de brotes vegetativos. En cosecha se evaluó firmeza de pulpa y contenido de sólidos solubles y almidón. Para la mayoría de las condiciones, los efectos ‘MA x producto’ y ‘producto’ sobre la brotación no fueron significativos, mostrando significancia el efecto ‘MA’. Los tratamientos en el segundo y tercer momento mostraron un significativo incremento del porcentaje de yemas brotadas con respecto al control, mientras que los tratamientos aplicados en el primer momento presentaron un adelanto de la misma.

Chemical rest breaking agents to compensate chilling requirements in apple (Malus domestica Borkh) are widely used in Uruguay (34º 37’ SL). This study evaluated the response to the application of rest breaking products in two varieties (Red Chief and Granny Smith), in three moments (AT), during 2005 and 2006. Treatments were evaluated in a factorial arrangement with two factors, product and moment. Products evaluated were: Hydrogen Cyanamide (2.5%), mineral paraffinic oil (3%), refined paraffinic mineral oil (2%) and a mixture of Hydrogen Cyanamide (0.75%) and paraffinic mineral oil (2%). The first application was performed at 250 CU (UTAH model) (during the first 15 days of August), and the following the first and third week of September. Beginning of the endodormancy release was determined when 50% of leaf fell, and completion was defined when 50% of one year old buds sprouted in a grow chamber. Budbreak percentage under field conditions was evaluated weekly, and new shoot length was quantified. At harvest, flesh firmness, soluble solids and starch content were measured. For most cases, ‘AT x product’ interaction and ‘product’ effect on budbreak percentage were not significant, while ‘AT’ effect was significant. Chemical products applied at the second and third AT significantly increased budbreak percentage with respect to control, while products applied first triggered earlier budbreak.

La cuantificación del frío invernal se realiza actualmente en Uruguay con los modelos UTAH y HF, aunque existe evidencia de la falta de ajuste en relación al comportamiento fenológico de la mayoría de los cultivares. Dada la amplia utilización de productos compensadores de frío en cultivos de manzana (Malus domestica), la adecuada cuantificación del frío invernal debería ser un insumo clave para la determinación de las necesidades de aplicación y el momento de su realización. El presente trabajo consistió en cuantificar el frío ocurrido durante el período de endodormición con seis modelos, en dos cultivares de manzana (Red Chief, Granny Smith), evaluando su performance según parámetros del desarrollo del proceso de brotación. Los modelos utilizados fueron HF, UTAH, UTAH+, Modelo Dinámico, North Carolina Model y Modelo para condiciones Subtropicales. El inicio del proceso de salida de endodormición se fijó cuando se alcanzó el 50% de la caída de hojas y su finalización fue definida en cámara de crecimiento controlado cuando se alcanzó el 50% de brotación en brindillas. Si bien el modelo Dinámico se muestra como el más promisorio, para determinar el ajuste de un modelo es necesario un mayor número de años.

In Uruguay UTAH and CH models are usually applied for estimation of chilling accumulation, regardless of which specie or cultivar is considered, although there are evidences of lack of fitness to the phenologyc behaviour of the most cultivars. Chemical rest breaking agents to compensate the chilling requirements in apple (Malus domestica Borkh) are widely used and winter chill quantification should be a relevant issue to adjust this technique. The objective of this work was to quantify the occurrence of winter chill during the endodormancy period with six models, in two apple cultivars (‘Red Chief’, ‘Granny Smith’), according to development indicators of sprouting process. The models used were CH, UTAH, UTAH+, Dynamic Model, North Carolina Model and Model for Subtropical Conditions. Beginning of the endodormancy release was considered when 50% of leaf fall was reached and the end of the process when 50% of one-year-old shoot buds sprouted in a forcing chamber. Although the Dynamic model appears to be more promising, a longer evaluating period is needed to evaluate the fitness of these models.