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Thermal time models have been used to predict the development of many different species, including grapevine (Vitis vinifera L.). These models normally assume that there is a linear relationship between temperature and plant development. The goal of this study was to estimate the base temperature and duration in terms of thermal time for predicting veraison for four grapevine cultivars. Historical phenological data for four cultivars that were collected in the Pacific Northwest were used to develop the thermal time model. Base temperatures (T b) of 0 and 10 °C and the best estimated T b using three different methods were evaluated for predicting veraison in grapevine. Thermal time requirements for each individual cultivar were evaluated through analysis of variance, and means were compared using the Fisher's test. The methods that were applied to estimate T b for the development of wine grapes included the least standard deviation in heat units, the regression coefficient, and the development rate method. The estimated T b varied among methods and cultivars. The development rate method provided the lowest T b values for all cultivars. For the three methods, Chardonnay had the lowest T b ranging from 8.7 to 10.7 °C, while the highest T b values were obtained for Riesling and Cabernet Sauvignon with 11.8 and 12.8 °C, respectively. Thermal time also differed among cultivars, when either the fixed or estimated T b was used. Predictions of the beginning of ripening with the estimated temperature resulted in the lowest variation in real days when compared with predictions using T b = 0 or 10 °C, regardless of the method that was used to estimate the T b.

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-Data was analyzed on development of the solanaceen fruit crop Cape gooseberry to evaluate how well a classical thermal time model could describe node appearance in different environments. The data used in the analysis were obtained from experiments conducted in Colombia in open fields and greenhouse condition at two locations with different climate. An empirical, non linear segmented model was used to estimate the base temperature and to parameterize the model for simulation of node appearance vs. time. The base temperature (Tb) used to calculate the thermal time (TT, o Cd) for node appearance was estimated to be 6.29 o C. The slope of the first linear segment was 0.023 nodes per TT and 0.008 for the second linear segment. The time at which the slope of node apperance changed was 1039.5 o Cd after transplanting, determined from a statistical analysis of model for the first segment. When these coefficients were used to predict node appearance at all locations, the model successfully fit the observed data (RSME=2.1), especially for the first segment where node appearance was more homogeneous than the second segment. More nodes were produced by plants grown under greenhouse conditions and minimum and maximum rates of node appearance rates were also higher. Index terms: Nodes, simulation, thermal time, base temperature, Cape gooseberry. TEMPERATURA BASE E MODELO DE SIMULAÇÃO DA APARIÇÃO DE NÓS EM PLANTAS DE FISALIS (Physalis peruviana L.)RESUMO -Dados analisados durante o desenvolvimento de fisalis, espécie frutífera da família das solanáceas, foram usados para avaliar a aparição de nós em diferentes condições ambientais através de um modelo clássico termal de tempo. Os dados usados na análise foram obtidos de experimentos conduzidos em dois locais, com clima diferente, em campos abertos e em condições de estufa, na Colômbia. O modelo não-linear empírico segmentado foi usado para estimar a temperatura-base, e para estabelecer os parâmetros do modelo da simulação da aparição de nós em função do tempo. A temperatura-base (Tb) usada para calcular o tempo termal (TT, ºCd) para a aparição de nós foi 6,29 ºC. A inclinação do segmento linear foi de 0,023 e de 0,008 nós por TT, para o primeiro e segundo segmentos lineares, respectivamente. O tempo estimado para a aparição do nó foi de 1.039,5 ºCd depois do transplante, determinado a partir de uma análise estatística do modelo do primeiro segmento. Quando esses coeficientes foram usados para predizer a aparição de nós em todas as locações, o modelo ajustou-se dados observados adequadamente (RSME=2,1), especialmente para o primeiro segmento, onde a aparição de nós foi mais homogênea do que no segundo segmento. O número de nós e as taxas mínimas e máximas de aparição de nós foram maiores em plantas cultivadas em condições de estufa do que em plantas cultivadas nas demais condições. Termos para indexação: Nós, simulação, tempo termal, temperatura-base, uchuva.

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