Carbon isotope discrimination and transpiration efficiency in common bean

Se midieron los valores de discriminacion de isotopos de carbono (delta) en diversas lineas geneticas de frijol como indicadores de la eficiencia en el uso de agua. Empleando las mediciones delta en linea, habia una estrecha concordancia entre los valores delta observados y aquellos pronosticados por los modelos delta de fotosintesis C3. Ademas, los valores delta tambien se correlacionaron significativamente con estimaciones de eficiencia de transpiracion (W) medidas en las plantas sembradas en macetas al aire libre a largo plazo. Basado en la raza ancestral y el centro de domesticacion, no se presentaron diferencias significativas en W o delta. Sin embargo, se presentaron diferencias cuando los cv. se analizaron con base en la region geografica para la cual se habian desarrollado. En prom., las lineas desarrolladas para America Central y del Sur presentaron valores de W significativamente mayores (0.63 vs. 0.57 mmol/mol, resp.) y valores delta inferiores (21.07 vs. 21.51 por ciento, resp.) que las lineas desarrolladas para America del Norte. Tambien hubo diferencias pequenas pero significativas en los sesgos de las relaciones entre delta y W que dependieron de la region geografica para las cuales las lineas se habian desarrollado. Las lineas norteamericanas de frijol comun presentaron una relacion mas estrecha entre estos 2 parametros que las lineas de America Central y del Sur. La base para estas diferencias evidentes en la eficiencia de transpiracion no es clara, pero puede haberse relacionado con la variacion en las conductancias foliares o los movimientos foliares paraheliotropicos entre los 2 grupos. (RA-CIAT) spa

Carbon isotope discrimination (delta) values were measured in diverse genetic lines of common bean (Phaseolus vulgaris L.) as indicators of water-use efficiency. Using on-line delta measurements, there was a close agreement between observed delta values and those predicted by C3-photosynthesis delta models. Additionally, delta values were also significantly correlated with transpiration efficiency estimates (W) measured in potted plants grown outdoors on a long-term basis. Based on ancestral race and domestication center, there were no significant differences in W or delta. However, differences occurred when cultivars were analyzed on the basis of the geographic region for which they had been developed. On average, lines developed for Central and South America exhibited significantly higher W values (0.63 vs. 0.57 mmol/mol, respectively) and lower delta values (21.07 vs. 21.51 percent, respectively) than did lines developed for North America. There were also small, but significant differences in the slopes of the relations between delta and W that were dependent on the geographic region for which lines had been developed. North American common bean lines exhibited a steeper relationship between these two parameters than did Central-South American lines. The basis for these apparent differences in transpiration efficiency is unclear, but may have been associated with variation in leaf conductances or paraheliotropic leaf movements among the two groups. (AS) eng