Carbon isotope discrimination as a tool to improve water-use efficiency in tomato

Carbon isotope discrimination (Delta) is a property that may be used to improve water-use efficiency (WUE). This study tested the association between Delta and WUE with plant materials and growth conditions likely to disrupt the link between Delta and WUE, The cultivated tomato, Lycopersicon esculentum Mill. cv. UC82B, a drought-resistant related species, L. pennellii (Cor.) D'Arcy accession LA716, and the F-1 and F-2 generations of the L. esculentum X L. pennellii cross were grown in containers in wet and dry field environments. The wet environment was repeated in a second year and plants were split into groups terminated early and late in the season. The F-1 generation had greater mean WUE and dry weight (DW) than L. escelentum, but the DW advantage was not maintained in the F-2 generation. Low Delta of L. pennellii suggested that leaf WUE was high, but its whole plant WUE varied relative to the other plant materials in the different environments. There was a negative correlation between Delta and WUE in the F-1 generation, and WUE was generally positively correlated with DW. However, low Delta was associated with large DW in only one environment and with small DW in three environments. Averaged across environments, the top 10% of the plants ranked by WUE had 47% greater WUE than the bottom 10%. In comparison, the bottom 10% ranked by Delta had an average of 16% greater WUE than the top Delta group, but in three of the four environments the bottom group accumulated 33 to 47% less DW than the top Delta group. This study on tomato suggests that WUE can be increased by selecting low Delta, but selecting low Delta done may identify a subpopulation of small plants. Dry weight could probably be increased by traditional breeding techniques.