Relationship between carbohydrate partitioning and drought resistance in common bean.

Drought is a major yield constraint in common bean (Phaseolus vulgaris L.). Pulse-chase (14)C-labelling experiments were performed using Pinto Villa (drought resistant) and Canario 60 (drought sensitive) cultivars, grown under optimal irrigation and water-deficit conditions. Starch and the radioactive label incorporated into starch were measured in leaves and pods at different time points, between the initiation of pod development and the production of mature pods. The water-stress treatment induced a higher starch accumulation in the drought-resistant cultivar pods than in those of the drought-sensitive cultivar. This effect was more noticeable during the early stages of pod development. Consistently, a reduction of starch content occurred in the leaves of the drought-resistant cultivar during the grain-filling stage. Furthermore, a synchronized accumulation of sucrose was observed in immature pods of this cultivar. These data indicate that carbohydrate partitioning is affected by drought in common bean, and that the modulation of this partitioning towards seed filling has been a successful strategy in the development of drought-resistant cultivars. In addition, our results suggest that, in the drought-resistant cultivar, the efficient carbon mobilization towards the seeds in response to water limitation is favoured by a mechanism that implies a more effective sucrose transport.