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eturn to table of

eturn to table of contents • Based on daily silk and cob measurements during pollination, the developing ear focuses the majority of its resources on silk growth in order to better catch viable pollen. • After a few days, silk growth slows, and the developing ear focuses its resources on cob growth in order to provide space and support for developing kernels. • The probability of successful pollination decreases as silks enter the latter phases of their life cycles. Silk Length (inches) 7 6 5 4 3 2 1 0 Sums of Silk Growth for Positions 5, 15, 25, and 35 and Total Cob Volume During Pollination Silk Growth Field is 50% Silk on Day 4 Cob Growth 1 2 3 4 5 6 7 8 9 10 11 12 Sample Day 14 12 10 8 6 4 2 0 Cob Volume (cubic inches) Covered ear (silks not exposed to pollen). Normal ear (silks exposed to pollen daily). Silks remain attached to the developing ovule until the ovule is fertilized. After the male and female gametes have fused, the developing ovule creates an abscission layer at the base of the silk. The silk no longer receives water and nutrients, causing the silk to turn brown and die. Usually a silk will start to turn brown about one day after successful fertilization. A more accurate and timely method to estimate the percent of successful pollination in a field is the following method: 1. Remove the ear from the plant. 2. Gently peel the husks from the ear so that the silks are disturbed as little as possible. 3. Grab the ear by the base and hold the ear so that the tip is pointing toward the ground. 4. Gently shake the ear. Silks will fall from fertilized ovules, while silks of ovules not fertilized will remain attached to the developing ovules. missing kernels. Under certain environmental conditions, some hybrids may produce ears with a few missing kernels at the base of the ear even when moisture and pollination conditions appear to be ideal. In these studies, total growth of silks at the very base of the ear was less than total silk growth along the rest of the ear (see “Cumulative Growth During Pollination”). The combination of slightly less total silk growth at the base of the ear and the tendency for silks to occasionally not emerge from the husk may at least partially explain this incomplete kernel fill. The crown of the mature corn kernel has a silk scar where the silk was attached to the developing ovule. This silk scar can be difficult to see on kernels of some corn hybrids. The photo below is of a corn line that shows a prominent silk scar at maturity. 22 5. Percent pollination is equal to the percent of ovules with no silks attached. A few silks may remain attached to ovules after pollination is complete. In this study, the silks that were still attached did not grow past the tip of the husk (see picture above). When this occurs, the end result is a mature ear with a few

eturn to table of contents ESTIMATING GRAIN YIELD WHEN INCOMPLETE POLLINATION OCCURS Grain yield per ear is a function of the total number of kernels produced multiplied by the weights of these individual kernels. In these studies, grain yield per ear correlated very highly with the number of kernels produced per ear. A small loss in kernel number does not substantially reduce grain yield because the kernels surrounding the area of the missing kernel will often compensate by becoming a bit larger. However, as the loss in kernel count becomes excessive, the remaining kernels on the ear cannot grow sufficiently to compensate for the loss in kernel numbers. Ears produced on “Day 5” and “Day 8” have different appearances but similar grain yields and kernel counts. Corn ears will often compensate for poor kernel fill at the base of the ear by increasing the kernel fill at the tip. The corn plant has a specific amount of resources that it will devote to grain fill. During the grain-filling interval, the corn plant will adapt to the best of its ability with the resources available to produce maximum yield of the viable kernels attached to the corn ear. Grain yield per acre is also a function of the total number of kernels per acre multiplied by the individual weights of these kernels. Approximately 85% of the variability in grain yield is related to the number of kernels produced per acre, while the remaining 15% of the variability in grain yield is related to the weights of these kernels (Otegui et al., 1995b). Corn growing on an acre of soil under specific environmental conditions is capable of devoting a certain amount of resources to grain yield. Two cornfields with similar grain yields will most likely have similar amounts of kernels produced per acre. The cornfield with the higher population will likely have more but smaller, harvested ears than a cornfield planted at a lower population. The challenge before agronomists and farmers is to manage an everchanging supply of resources so that the corn properly partitions these resources between vegetative and grain yield demands. Normal Ear* Day 2 Day 3 Day 4 *silks exposed to pollen daily Percent of Normal Ear Grain Harvest Wt (oz/ear) 120 100 80 60 40 20 8 7 6 5 4 3 2 1 0 0 Day 1 Day 5 Day 6 Day 7 Day 8 Grain Weight and Kernel Count of Ears Exposed to Pollen for One Day Field is 50% Silk on Day 4 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Sample Day Day 8 Day 9 Day 9 Day 10 Day 10 Day 11 Kernel Weight Kernel Count Grain Yield Per Ear as a Function of Kernels Per Ear y = 0.0098x R 2 = 0.95 Day 11 0 100 200 300 400 500 600 700 800 Kernels per Ear 23

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