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Dry Matter Accumulation in Kernels of Maize¹

Selection in a breeding program for physiological traits should not be initiated without knowledge of critical growth stages for the crop. The granin yield of maize (Zea mays L.) is the integral of kernel dry matter accumulation over time. The rate and duration of kernel fill have been suggested as factors which might be improved through selection and result in yield improvement. The purpose of these experiments was to follow kernel development at three positions on the ear when treatments were imposed which altered assimilate supply to the ear.

Two maize hybrids, Pioneer brand '3388' and '3369A,' which differed in the yield components, kernel rows ear^-1, and kernel weight, where grown in field plots. Treatments were applied at 50% stand density, shoot bagging ears to allow complete pollination on single day, and 50% leaf area removal. Kernel growth rates were determined for kernels at the base, middle, and tip regions of the ears. Hybrid 3369A had more rapid rates of kernel dry matter accumulation than did 3388 in both years.

Treatments which affected assimilate supply, i.e., thinning and leaf area removal, affected kernel number (ear row)^-1through variations in the cessation of kernel development at the tip of the ears. Rates of kernel dry matter accumulation were similar for kernels from basal and middle regions of the ears, regardless of assimilate supply. Tip kernels may have filled at slower rates than did kernels from the other two regions. Altered duration of the linear phase of kernel dry matter accumulation due to treatments affecting assimilate supply was suggested as one cause of variations in kernel weight on an ear as well as between ears of the same hybrid. A critical stage in the development of maize that is highly dependent on assimilate supply is the 2- to 3-week period after 50% silking; the period when final kernel number is determined.

Key Words: Source-sink • Growth rates • Yield components • Carbohydrate supply • Defoliation, • Zea mays L

² Pioneer Hi-Bred International, Inc., P.O. Box 85, Johnston, IA 50131.

Received for publication December 10, 1979.

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