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Background. Abiotic constraints, historical effects of the last glaciation, and differential dispersal, have been proposed as potential explanations to account for the latitudinal decrease in acorn size of wide-ranging oak species distributed in the U.S. and Canada. Hypothesis. We specifically tested the abiotic constraints hypothesis on oak acorn size in a geographical area without the counfounding influence of glaciation and related dispersal history. Data description. Acorns from seven populations of the white oak Quercus rugosa were collected, encompassing the distribution of the species in Mexico. Study site and years of study. Mexico, 2009Mexico, -2010. Results. Acorn length, width, mass and volume differed significantly among populations and indicated a marked clinal latitudinal reduction in acorn size. A multiple regression model revealed that this reduction in size (measured as acorn volume) can be explained by two important bioclimatic variables (growing season precipitation and growing season degree-days above 5 °C), while spatial variables (latitude and longitude) are not significant. Furthermore, germination percentage was significantly correlated to acorn mass and volume. Conclusions. The main determinants of the latitudinal decline in acorn size are climate factors constraining seed development. This decline is maladaptive for seedling establishment, with important implications for the delination of northern limits of species ranges. Key words: acorn size, climate factors, geographical variation, latitudinal distribution, Quercus. Determinantes climáticos del tamaño de las bellotas y el porcentaje de germinación de Quercus rugosa (Fagaceae) a lo largo de un gradiente latitudinal en México ResumenAntecedentes. Las restricciones abióticas, el efecto histórico de la última glaciación y la dispersión diferencial son posibles explicaciones para la disminución latitudinal del tamaño de las bellotas en especies de encinos de amplia distribución en los EE.UU. y Canadá. Hipótesis. Se probó específicamente la hipótesis de las restricciones abióticas sobre el tamaño de las bellotas de encinos en un área geográfica sin influencia de la historia de colonización postglacial. Descripción de datos. Se colectaron bellotas procedentes de siete poblaciones del encino blanco Quercus rugosa, abarcando la distribución de la especie en México. Sitio de estudio y fechas. México, 2009México, -2010 Resultados. La longitud de las bellotas, el ancho, la masa y el volumen difirieron significativamente entre las poblaciones y mostraron una marcada reducción latitudinal clinal en el tamaño de la bellota. Un modelo de regresión múltiple reveló que esta reducción en el tamaño (medido como volumen de bellota) puede explicarse por dos variables bioclimáticas importantes (precipitación en la temporada de crecimiento y días-grado por encima de 5 °C de la temporada de crecimiento), mientras que las variables espaciales (latitud y longitud) no fueron significativas. Adicionalmente, el porcentaje de germinación se correlacionó...

In time‐course experiments, the amounts of phytoalexin in hypocotyls of the resistant bean cultivar Flor de Mayo were determined after infection with Colletotrichum lindemuthianum. Phaseollin and phaseollidin accumulated as a defence response. However, phaseollidin accumulated earlier than phaseollin and at greater concentrations (155 + 14 compared with 120 + 9 μg g−1 fresh weight). Phaseollidin was found conjugated as a glucoside in the tissue. Fungal treatment apparently led to a decline of approximately 50% in phaseollidin conjugate after only 7 h after infection. Isolation of vacuoles confirmed the presence of phaseollidin glucosides in this organelle. Treatment of the tissue or isolated protoplasts with a fungal elicitor also produced a decrease, by half, of phaseollidin conjugate concentrations from vacuoles isolated from both sources. The contribution of pre‐existing pools of phaseollidin glycoside to the accumulation of this phytoalexin is discussed.