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Photosynthetic Differences among Lycopersicon Species and Triticum aestivum Cultivars

Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078

^* Corresponding author.

Leaf photosynthesis rate (A) and water use efficiency expressed as A/g_s (g_s, stomatal conductance) are controlled by stomatal properties and leaf internal anatomical and biochemical/physiological characteristics. Two germplasm entries were selected from each of the genera Triticum and Lycopersicon with contrasting drought resistance. Both drought resistant entries (L. pennellii and T. aestivum cv. TAM W- 101) had the greater A/g_s within each pair. Of the two entries with high A/g_s, L. pennellii had lower A and TAM-101 had higher A than the respective counterpart with low A/g_s (L. esculentum and T. aestivum cv. Sturdy, respectively). Comparison of photosynthetic stomatal supply capacities and mesophyll biochemical demand capacities suggested that differences in mean A and A/g_s in contrasting tomato species were dependent on the lower mean g_s of L. pennellii than L. esculentum, because in leaves with equal g_s the balance between stomatal supply and mesophyll demand was identical. In wheat leaves operating at identical g_s, however, TAM W-101 had greater mesophyll capacity than Sturdy. Lower A and A/g_s of Sturdy than TAM W-101 was correlated with lower carboxylation efficiency and lower light and CO₂ saturated A, factors associated with the photosynthetic biochemistry of mesophyll tissue. At identical g_s, the balance between mesophyll and stomatal capacities and limitations of TAM W-101 was the same as for the two tomato species. This suggested that for these three entries (L. esculentum, L. pennellii, and TAM W-101), the differences in A and A/g_s resulted from differences in the mean and range of g_s. Sturdy was unique by having low A and low A/g_s, a result of poor mesophyll capacity compared to the other entries.

Received for publication January 29, 1993.