Water is vital for plants. A reduction in water availability may affect crops transpiration and leaf growth. The objective of this study was to determine the response of transpiration and leaf growth to the fraction of transpirable soil water (FTSW) in two potato clones (an old and a new) adapted to Southern Brazil. Three experiments were carried out under a plastic shelter in Santa Maria, RS, Brazil, using two potato clones, an old ('Macaca') and a new ('SMINIA793101-3'). Two of the experiments were in spring (planting on 08/20/2008 (E1) and 10/20/2008 (E2)), and one in fall, (planting on 03/25/2009 (E3)). Soil water, represented by the FTSW, transpiration and leaf growth were measured on a daily basis during the period of soil drying. The threshold FTSW, when transpiration begins to be affected, which is an indicator of stomata closure, was 0.39, 0.47 and 0.28 for the clone 'Macaca' and 0.47, 0.49 and 0.33 for 'SMINIA793101-3' in E1, E2 and E3, respectively, whereas leaf growth was affected at a higher FTSW threshold for 'Macaca'. These results indicate that 'SMINIA793101-3' is more tolerant to soil water deficit than 'Macaca'.
Solanum tuberosum L.; water stress; stomata closure; plant breeding
