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SUMMARY

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eturn to table of contents RELATING SILK EMERGENCE AT POLLINATION TO KERNEL SET AT HARVEST by Stephen D. Strachan, Ph.D., DuPont Research Scientist SUMMARY • Maximum kernel set and grain yield occur when pollen shed coincides with rapid silk growth. • Silks attached near the base of the ear emerge first, and silk emergence progresses toward the tip of the ear. Kernel set also progresses from the base to the tip of the ear. • Under the environmental conditions of this study, silks remained receptive to pollination for about five to six days. Maximum silk growth was about 1.6 inches per day. • For this study, the number of kernels per ear correlated highly (r 2 = 0.95) with grain yield per ear. • Grain yield was constant if the total number of kernels/ear was constant. The corn ear may compensate for poor kernel set at the base by producing more kernels at the tip. 18

eturn to table of contents INTRODUCTION Successful harvest of corn seed or grain requires adequate pollen when silks are receptive during pollination. Pollen shed, or anthesis, is controlled by a combination of genetic and environmental factors. The genetic background of the corn plant provides a general baseline for the necessary number of growing degree units until anthesis. Once pollen grains have matured inside corn anthers, these anthers begin to dry and dehisce. As anthers dehisce, they allow pollen grains to fall into the open air and possibly land on receptive corn silks. The process of pollen growth and maturation inside corn anthers with the subsequent drying and splitting of corn anthers to allow pollen release is similar to the process of growth and maturity in soybean with the drying and splitting of the pods to release the soybean seeds. Environmental conditions, such as relative humidity and temperature, are contributing factors for anther dehiscence. During summer nights, temperatures are relatively cooler and relative humidities higher, so anthers maintain a more hydrated state. As the morning progresses, temperatures tend to increase and relative humidities decrease, thus drying corn anthers. Anthers containing mature pollen typically shed pollen around mid-morning. A tassel will normally shed pollen for about five days. Silk emergence is also controlled by a combination of genetic and environmental factors. The genetic background of the corn plant provides a general baseline for the necessary number of growing degree units until silks emerge. Temperature and available moisture also play extremely critical roles for silk emergence, elongation, and exsertion past the tip of the husk. Under ideal temperature and moisture conditions for corn growth, silk exsertion is very rapid and consistent throughout similar areas of the field. However, if corn plants are subjected to dry conditions or drought stress, silk emergence may be delayed and rates of silk growth reduced. Changes in silk growth may affect the number of kernels set on the harvested ear. FIELD STUDY CONDUCTED DuPont conducted a field study relating silk growth at pollination to kernel set at harvest. Ear shoots were covered before any silks were exposed. On the day before silks were to be exposed to pollen, researchers selected 20 ear shoots, clipped the silks back to the tip of the husk, and covered them with ear shoot bags for 1 day. The next day, the shoot bags were removed from 10 of the shoots, exposing the silks to open pollination for 1 day. These ear shoots were then covered with bags to eliminate additional exposure to pollen. The remaining 10 ears were hand-harvested. New silk growth was measured from the tip of the husk for silks attached to developing ovules in kernel positions 5, 15, 25, and 35 from the base of the ear. Cob length and width were also measured. Silk lengths were measured by covering the exserted silks with red “carpenter’s chalk.” The ears were carefully extracted from the husks with silks still attached, and the lengths of red silks at the various kernel positions were measured. This procedure was repeated daily during the entire pollination window. Environmental and soil moisture conditions were nearly ideal for corn growth and pollination. After the crop matured, the selected ears were harvested, kernels per ear were counted, and grain yield per ear was measured. RELATING DAILY SILK GROWTH TO GRAIN YIELD The following series of pictures illustrates daily silk growth and kernel set of matched ears during pollination. Data in the graphs are averages of 10 replications. Pictures for a particular day represent average responses. Pictures for the 12 days during pollination follow the same format: a picture of the developing ear and a picture of a corresponding ear at harvest. Silks first emerge from near the base of the ear. Silks must intercept pollen for kernel set to occur. Initially, silks grow most rapidly at the base of the ear. Kernel set matches silk emergence. 19

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