Leaf Transpiration Efficiency of Sweet Corn Varieties from Three Eras of Breeding

When measured under midday field conditions, modern varieties of maize ( Zea mays L.) often have substomatal carbon dioxide concentration (C i ) values in excess of those required to saturate the photosynthetic carbon dioxide assimilation rate (A). This results in lower leaf transpiration efficiency (TE), the ratio of photosynthesis to transpiration, than potentially achievable for a given rate of photosynthesis. In some other crops, breeding has indirectly resulted in a large increase in stomatal conductance (g s ), which would decrease TE. I tested whether this occurred in sweet corn by comparing five open‐pollinated varieties released before 1903 with four standard hybrid varieties released in the mid‐1900s and four varieties released after 1990. Leaf gas exchange of each variety was measured under ambient midday field conditions on eight sunny days over two seasons in Beltsville, MD. Although there were significant differences among varieties in g s , A, C i , and TE, no effect of era was significant for any variable except A. Of the four modern varieties tested, two had the highest g s and two had the lowest g s of any of the varieties compared, with high g s associated with low TE. These four varieties were further compared in a third year and were found to differ consistently in leaf TE but not in A. It is concluded that breeding over the last century has not increased g s or decreased leaf TE in sweet corn but that there is significant variation in TE among modern sweet corn varieties.