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Photosynthesis, Stomatal Resistance, and Enzyme Activities in Relation to Yield of Field-grown Dry Bean Varieties¹

Photosynthetic rates, stomatal resistances and the activities of three enzymes; ribulose bisphosphate carboxylase (RuBPCase), malate dehydrogenase (MDH), glycolate oxidase (GAO) were determined for nine fieldgrown dry bean (Phaseolus vulgaris L.) varieties. Measurements were made during several developmental stages; vegetative growth, flowering, early pod set, and late pod set. All data were compared to biological and seed yields using seasonal averages as well as using data from each developmental stage separately.

Photosynthetic rates and RuBPCase activities were highest at early pod set, which was the only developmental stage where they were significantly correlated with biological yields. Also at pod set MDH activities were significantly correlated with both seed yield and harvest index, and GAO activity was correlated with biological yield. GAO activity was highest at flowering. The amount of the increase in photosynthesis from flowering to pod set of each variety was correlated positively with its final seed yield.

While photosynthetic rates at pod set were positively correlated with both biological and seed yield in eight of the varieties, in one variety high seed yields were associated with very low photosynthetic rates. This variety, however, also had an exceptionally high harvest index and high MDH and GAO activities. Thus high seed yields are not necessarily associated with high photosynthetic rates but may result from a more efficient utilization of photosynthate.

Key Words: Phaseolus vulgaris L. • Ribulose bisphosphate carboxylase • Glycolate oxidase • Malate dehydrogenase • Developmental stage

² Dep. of Botany, Duke Univ., Durham, NC 27706; Faculty Agronomia, Depto. Fitotechia, Universidad Catholica de Chile Casilla l14-D Santiago, Chile (663193); Dep. of Vegetable Crops, Cornell Univ., Ithaca, NY 14853; and Dep. of Horticultural Science and Landscape Architecture, Univ. of Minnesota, St. Paul, MN 55108, respectively.

Received for publication July 2, 1976.