Measuring canopy cover

Evaluation of some water-use-efficiency related changes in processing tomatoes in California

Water use efficiency (WUE) has inadvertently increased in the past 30 years during tomato breeding in California. Evapotranspiration rates (i.e., water loss via evaporation and plant use) have kept constant at an average of 648 mm, but yields have increased more than 50% since the 1970s to currently over 81 Mg/ha (Hanson and May 2006).

This study compared 8 tomato cultivars released from 1936-2002 to identify particular traits, e.g., stomatal conductance, photosynthetic capacity or root depth, that may have evolved during the breeding process for maximizing yields, or alternatively, improving pest resistance to tomato cultivars.

The preliminary results suggest that canopy architecture, leaf area per plant, and stem biomass has decreased along with an increase in photosynthetic rates and more fruits per branch, i.e., harvest index (Figures 1). These findings can contribute to the understanding of traits involved in the increased WUE in processing tomato and serve for breeding programs as information on which specific physiological, phenological or morphological traits may further increase WUE in tomatoes as well as other crops.

Average photosynthetic rate of four cultivars after irrigation. Years of release from left to right are 1930s, 1960s, 1980s and 2000s. (Barrios-Masias, unpubl. data)

Cultivar evolution of processing tomatoes