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Effect of Elevated Growing-Point Temperature on Maize Growth and Yield¹

Clipping of early leaves has been shown to increase the harvest index (HI) or maize (Zea mays L.). In a preliminary greenhouse study, we found that early leaf clipping increased the growing point (GP) temperature of the plant. The objective of this study was to determine if leaf clipping of corn resulted in GP heating in the field, and to determine if the previously observed increase in HI of corn following early leaf clipping was associated with altered GP temperature. Field experiments were conducted in 1978 and 1979 at St. Paul, MN. Growing point heating treatments were designed to simulate the effect of increased GP temperature following early clipping without actually removing the leaves. Clipping at the five-leaf stage (LS) increased GP temperature in the field by as much as 5°C when measured at midday. Clipping and heating increased HI by 18 and 15%, respectively, when averaged over both years. Clipping and heating at the five-LS reduced leaf area by 14 and 7%, respectively. Averaged over both years, both clipping and heating at the five-LS significantly reduced tillering. It appears that the effect of early leaf clipping on corn growth may in part be a response to altered GP temperature. We propose a physiological hypothesis for the effects observed following both early leaf clipping and GP heating.

Key Words: Zea mays L. • Growing point heating • Dry matter partitioning • Early leaf clipping

² Research agronomist, Pioneer Hi-Bred Int. Eastern Division, Tipton, IN 46072; and professor in the Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108.

Received for publication February 10, 1984.