Leaf Transpiration Effi ciency of Sweet Corn Varieties from Three Eras of Breeding

When measured under midday fi eld conditions, modern varieties of maize (Zea mays L.) often have substomatal carbon dioxide concentration (Ci) values in excess of those required to saturate the photosynthetic carbon dioxide assimilation rate (A). This results in lower leaf transpiration effi ciency (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 (gs), which would decrease TE. I tested whether this occurred in sweet corn by comparing fi ve 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 fi eld conditions on eight sunny days over two seasons in Beltsville, MD. Although there were signifi cant differences among varieties in gs, A, Ci, and TE, no effect of era was signifi cant for any variable except A. Of the four modern varieties tested, two had the highest gs and two had the lowest gs of any of the varieties compared, with high gs 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 gs or decreased leaf TE in sweet corn but that there is signifi cant variation in TE among modern sweet corn varieties. J.A. Bunce, USDA-ARS, Crop Systems and Global Change Lab., Beltsville Agricultural Research Center, 10300 Baltimore Ave., Beltsville MD 20705-2350. Received 7 Sept. 2010. *Corresponding author ( [email protected]). Abbreviations: A, photosynthetic carbon dioxide assimilation rate, ASD, air saturation defi cit for water vapor, Ci, substomatal carbon dioxide concentration, gs, stomatal conductance, LAVPD, leaf to air diff erence in water vapor pressure; (se), sugary enhancer; (su) normal sugary; TE, transpiration effi ciency. Published in Crop Sci. 51:793–799 (2011). doi: 10.2135/cropsci2010.09.0509 Published online 27 Jan. 2011. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.