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© 2003 Plant Management Network.
Accepted for publication 19 September 2003. Published 27 October 2003.

Defoliation Affects Grain Yield, Protein, and Oil of TopCross High-Oil Corn

Peter R. Thomison, Department of Horticulture and Crop Science, Ohio State University, Columbus 43210; and Emerson D. Nafziger, Department of Crop Sciences, University of Illinois, 1102 Goodwin Avenue, Urbana 61801

Corresponding author: Peter R. Thomison. thomison.1@osu.edu

Thomison, P. R., and Nafziger, E. D. 2003. Defoliation affects grain yield, protein, and oil of TopCross high-oil corn. Online. Crop Management doi:10.1094/CM-2003-1027-01-RS.

Abstract

The TopCross grain production system, in which about 90 percent of the plants in a corn (Zea mays L.) field are male-sterile and the remainder serves to transmit the high-oil character through pollen, is widely used to produce high-oil corn (HOC). In the TopCross system, two types of corn are planted as a physical mixture (a TC Blend). It is not known whether defoliation by hail or other factors affects yield of TC Blends the same as it does normal hybrids, nor whether defoliation affects grain quality, particularly oil content, on which premiums are based. In studies conducted over two years in Ohio and three years in Illinois, grain yields decreased as leaf removal increased in severity, and as time of defoliation neared tassel emergence. The greatest yield reductions caused by defoliation occurred at or near flowering, with complete defoliation at flowering reducing yields by 95 percent or more. Grain oil content was usually less affected by defoliation than grain yield, and it typically required defoliation sufficient to reduce yield by more than 50 percent, and sometimes as high as 70 percent, in order to decrease oil content. Grain oil content was reduced as much as 30 to 40 percent with complete defoliation during late vegetative, flowering, and early grain fill, whereas protein content was increased as much as 50 percent. High-oil corn TC Blends and a conventional hybrid counterpart exhibited similar responses to defoliation for grain yield, and oil and protein content in the Ohio study. Since premiums for contract production of HOC are based on grain oil concentration, the lower oil content caused by severe defoliation may result in reduced premiums.

Introduction

Effects of defoliation on the grain yield of corn hybrids have been well documented in numerous research studies (4,7,8). Results of this research have served as the basis for charts used by crop-hail insurance adjustors in determining grain yield losses due to leaf blade removal by hail (13), as well as wind and frosts. The charts have also been used to estimate effects on yield from other types of mechanical injury such as the destruction of viable leaf tissue by insect feeding, diseases, and/or chemicals. Reduction in corn yield has been shown to be directly proportional to the percentage leaf area destroyed (7). The degree of yield loss caused by defoliation is dependent not only on leaf area destroyed, but also on the growth stage when defoliation occurs. Yield losses from defoliation damage are greatest during the late vegetative and reproductive stages. Although defoliation may cause lower kernel weight and test weight (8,17), little information is available on the effects of defoliation on grain quality especially as it relates to the oil, protein, and starch composition of corn.

High-oil corn is attractive as a livestock feed because it has greater energy value than normal yellow dent corn and can replace more expensive dietary sources of fats and proteins. Feeding trials with HOC indicate that it has improved feed efficiency and results in increased rate of gain over conventional corn (11).

The TopCross grain production system, licensed by DuPont Specialty Grains, is the most widely used method of producing HOC in the US (18). The TopCross system uses a blend (TC Blend) of two types of maize (3). One type, referred to as the grain parent, is a cytoplasmic male sterile (produces no viable pollen) elite hybrid that comprises 90 to 92% of the seed in the blend. The second type, comprising 8 to 10% of the seed in the blend, is a high-oil pollinator. The primary function of pollinators is to provide pollen to male sterile grain parents; however, they contribute little to grain yield. The pollen shed from these pollinator plants contain genes that cause production of kernels with larger than average embryos (11). Since most of the oil and essential amino acids are in the embryo, the increased embryo size of HOC results in greater oil content, and enhances the protein quality of the grain (11). Following the introduction of the TopCross system, HOC production in the US increased from less than 50,000 acres in 1992 to over 1,000,000 acres in 1999. However, since then, HOC production has dropped sharply with acres planted in 2002 estimated at less than 500,000 (18). Several factors have contributed to this decline, including greater production risks (1) and lower grain yields (16) associated with TopCross HOC production.

Limited information is available on changes in the chemical composition of kernels resulting from defoliation of corn. Singh and Nair (15) found that defoliation increased grain protein and decreased grain sucrose and reducing sugars. Johnson (10) reported that complete defoliation of nine commercial corn hybrids at the five-leaf stage (13) reduced grain protein from 11.4 to 10.7% but had no effect on oil content. So far as known, no studies have addressed the effects of leaf removal on the oil content of corn during grain fill.

Defoliation effects on the agronomic performance and grain quality of HOC corn, especially as it relates to the chemical composition of corn grain, are not known. Unlike commodity grain production, profitability in HOC is not only based on grain yields but also on the oil content of grain. Higher grain oil content commands higher premiums, and if grain oil content falls below a specified content (often in the range of 6.0 to 6.5% on a dry matter basis), no premium is offered. Therefore, HOC growers need to know the effects of defoliation on grain yields and oil content to assess the economic impact of leaf destruction and to successfully manage potential risks associated with this specialty crop.

The objective of this study was to evaluate the effects of defoliation on the agronomic performance and grain quality of TC Blends used in the HOC TopCross production system in different parts of the Corn Belt. Results of this study may serve as a basis for predicting grain quality and yield losses in HOC associated with leaf blade removal or destruction by mechanical or chemical injury, insect feeding, and/or foliar diseases.

Field Experiments to Assess Defoliation Effects

Field experiments were conducted in Illinois and in Ohio. In the Illinois experiments, defoliation effects on a HOC TC Blend at vegetative, flowering and grain fill stages were assessed in 1997 to 1999. In the Ohio experiments, the response of a HOC TC Blend to various late defoliation treatments during flowering and grain fill was compared to its conventional hybrid counterpart in 1996 and 1997.

Illinois experiments. In 1997 and 1998, the experiments were conducted in fields of a private cooperator near Champaign, IL. In 1999, the experiment was planted at the University of Illinois Crop Sciences Research and Education Center near Urbana. The HOC TC Blend Wyffels brand 7115TC was used all three years. The relative maturity of Wyffels 7115TC is 111 days. Plant populations (in plants per acre) at harvest in each year were as follows: 30,800 in 1997; 29,400 in 1998; and 30,500 in 1999.

A randomized complete-block design with three replicates was used. Plots four rows wide (30-inch row spacings) and 20 ft in length were established within each field, with four replications of the 15 treatments. Treatments consisted of complete defoliation at the V3/4 and V6/7 stages (14), 50 and 100% defoliation at the V9/10, V12/13, and V15/16 stages, and 25, 50, and 100% defoliation at the VT (tassel)/R1 (silking) and the R3 (milk) stage of grain development (14). The 25 and 50% defoliation treatments were imposed by cutting off the terminal part of each leaf to remove the appropriate amount of leaf area. The 100% defoliation treatment involved cutting at the collar all fully developed leaves on the plant. Defoliation treatments were imposed by hand as described by Hicks et al. (8). The leaf staging system used in this work is based on the number of leaves with their collar visible (14) and is about 1½ to 2 stages behind that used by hail adjusters, which is based on an indicator leaf that is mostly exposed but does not yet have its collar visible (13). Due to weather and other factors, actual treatment stages were up to one stage earlier than planned in some cases, and so are indicated as stage ranges.

Ohio experiments. Field experiments in 1996 were conducted at three locations: The Ohio State University (OSU) - Ohio Agricultural Research and Development Center (OARDC) Western Branch Research Farm (WBRF) near South Charleston; the OSU Waterman Farm in Columbus (OSUWF); and the Fayette County Extension Crop Diagnostic Farm near Washington Courthouse. Experiments in 1997 were established at four locations: the OSU Farm Science Review near London; the OSU-OARDC Agronomy Farm near Wooster; the WBRF; and the OSUWF. In 1996, a TC Blend, Pfister brand SuperKernoil SK2650-2, was compared with its normal-oil conventional hybrid counterpart, SK2650. In 1997, a different TC Blend, Pfister SuperKernoil SK2650-19 (the same TC Blend grain parent but different pollinator from that used in 1996), was compared to Pfister 2650. The relative maturity of Pfister brand 2650, SK2650-2, and SK2650-19 is 108 days. Plant population at harvest averaged 28,500 to 30000 plants per acre.

A randomized complete block field design with treatments in a split plot layout was replicated three times. The TC Blend and conventional hybrid counterpart (hereafter referred to as the check hybrid) were assigned to main plots and the defoliation treatments to subplots, four rows wide (30-inch row spacings) and 17.5-ft in length. In 1996, defoliation treatments were as follows: no defoliation, and 50 and 100% leaf blade removal at the R3 (milk) and R5 (full dent) stage of development. In 1997, the same treatments were used as in 1996, except that two additional treatments were established: 50 and 100% leaf blade removal at VT. The procedure used to defoliate plants was the same as that used in the Illinois experiments.

In both the Illinois and Ohio experiments, nutrient, insect, and weed management strategies appropriate for minimizing crop stress were followed. Tables 1 and 2 indicate soil types and planting dates associated with each experiment location. The previous crop at each location was soybean [Glycine max (L.) Merr.]. To minimize possible pollen contamination from the neighboring conventional hybrid counterpart as well as any nearby normal corn, the HOC TC Blend plots were planted in isolation at least 100 ft from normal corn hybrids. Plots were also planted with TC Blend seed as border (20 to 50 ft) on all sides of the isolation field.

Table 1. Field experiment locations and soil types in Illinois and Ohio.

Table 2. Corn planting dates and monthly precipitation totals (inches) for the Illinois and Ohio experimental locations.

^a Values in parentheses are departures from the 30-year average.

^b Cham. = Champaign, Col. = Columbus, S. Ch. = S. Charleston,
Wash. = Washington Courthouse.

Final plant stand and numbers of lodged stalks and barren plants (including plants with small, poorly developed ears) were recorded at maturity prior to harvest. Grain yields and moisture were taken on ears harvested from the center two rows of each plot, with yields adjusted to 15.5% moisture content. In the Ohio study, only ears from TC Blend grain parent plants were sampled for grain oil and protein analysis since pollinator plants generally produced small, poorly developed ears. Analyses of oil and protein content were conducted on shelled grain using near infrared transmission (NIT) spectroscopy (2) and are presented on a dry weight basis.

Data for each trait were subjected to analysis of variance at each location. Data were combined over years for analysis in the Illinois study, and combined over locations each year for analysis in the Ohio experiments. A mixed model was used with locations as random effects, and corn types (HOC TC Blend versus check hybrid) and defoliation treatments as fixed effects. Years were considered as random in the Illinois analysis. Years were examined separately in the Ohio analysis because the TC Blend and defoliation treatments differed each year. Least significant difference values for means separation were calculated according to McIntosh (12).

In the Illinois experiments, rainfall (Table 2) and temperatures (data not shown) were near normal during the 1997 to 1999 growing seasons and favorable for high corn yields. Climatic conditions varied considerably in the Ohio experiments, especially for the amount and distribution of precipitation during the growing season (Table 2). Excessive rainfall in April and May of 1996 delayed planting. Below average rainfall during August coupled with above average temperatures in July through September (data not shown) created moisture stress conditions that reduced corn yield potential. In 1997, although rainfall was generally below average in August and September, below average temperatures (data not shown) during grain fill limited moisture stress.

Grain Yield

Effects of defoliation on grain yield of HOTC at the various developmental stages were similar to those reported for normal corn (4,7,8). At all stages of development, yields decreased as the percentage of leaf tissue removed increased (Tables 3 and 4). The greatest yield reductions caused by defoliation occurred at and near VT, with complete defoliation at VT/R1 reducing yields by 95% or more. Yield losses from complete defoliation at R3 averaged 70 and 58% in the Illinois and Ohio studies, respectively (Tables 3 and 4). Yields were reduced 90% by complete defoliation at V15/16 in the Illinois study. Although the 100% defoliation treatments consistently reduced yields at all development stages, effects of 25% and 50% leaf removal were mixed and often had no impact on yield (Table 3). Effects of 50% leaf removal on grain yield were greatest at VT/R1, with yield reductions averaging 25 and 41% in the Illinois and Ohio studies, respectively (Table 3 and 4).

Table 3. Grain yield, and oil and protein content (%) of a high-
oil TC Blend with different defoliation treatments from V3/4 to
R3, averaged over three years (1997-1999), Illinois study.

^a Oil and protein by NIT, expressed on a dry weight basis.

Table 4. Grain yield, and oil and protein content of a high-oil (HO) TC Blend and its check hybrid with different defoliation treatments, averaged across three locations in 1996, and four locations in 1997, Ohio study.

^a Oil and protein by NIT, expressed on a dry weight basis.

^b Grain parent only.

^c NA; insufficient sample size and poor quality for NIT analysis.

In the Illinois study (Table 3), complete defoliation at V6/7 and R3 resulted in much larger yield reductions (37%, averaged across three years) in HOC than predicted by the NCIA charts (13) for normal corn (about 12%). However, defoliation effects at V6/7 were variable over years, with no loss in 1997, about 30% in 1998, and almost 70% in 1998 (data not shown). Other investigators (5,10) have also reported major stand and yield losses caused by complete defoliation at this early stage of development in normal corn. These atypical responses have been attributed to unfavorable growing conditions during regrowth following the defoliation event (wet, cold conditions or high temperatures). Though some seven inches of rain fell within 14 days after this treatment in 1998 and about three inches within the same period in 1999, temperatures were moderate and subsequent rainfall adequate for high yields. While wet weather after treatment might explain these yield losses, it is possible that other factors such as disease or patterns of rainfall later in the season (Table 2) contributed. Complete defoliation at R3 reduced yields 70%, whereas NCIA charts (13) indicated yield losses of 59%.

Results of the Ohio study also indicated that yield losses associated with defoliation of the HOC corn and check hybrid were higher (Table 4) than those estimated by NCIA charts (13). Some of the discrepancies in yield losses between the NCIA estimates and our results may be related to differences in the defoliation techniques used and weather conditions at the time of defoliation. Differences in hybrid response to defoliation may also be responsible for some of this variation. Past studies have indicated that corn hybrids and inbreds vary in their response to defoliation (7,8,19). In the Ohio experiment, the check hybrid showed yield reductions caused by defoliation as great as or greater than those associated with the TC Blend, which suggests that TC Blends and conventional hybrids may exhibit similar yield loss response to defoliation during grain fill (Table 4). Since only a limited number of HOC TC Blends were evaluated in this research, conclusions about yield responses of TopCross HOC to defoliation must be narrow.

Grain Oil and Protein Content

The oil content in grain from the non-defoliated TC Blends, averaged across years, was 7.6% and 6.7% in the Illinois and Ohio studies, respectively (Tables 3 and 4) which reflects the range in oil content found in HOC (18). The grain oil content of the check hybrid in the Ohio experiment averaged 3.7% (Table 4). Grain oil content from conventional corn hybrids typically ranges from about 3.5 to 4.0% (18).

Oil and protein content of grain from TC Blends and the check hybrid were significantly affected by leaf removal, with levels of oil decreased and protein increased by severe defoliation. The largest reductions in grain oil content were associated with 100% defoliation at V15/16, VT-R1, and R3 (Tables 3 and 4). In the Illinois study, complete defoliation at V15/16, VT-R1 and R3, reduced oil content 37 to 39% compared to the non-defoliated TC Blend (Table 3). The defoliation treatments prior to V15/16 and those treatments involving 25 or 50% leaf removal generally had negligible effects on oil content (Table 3). In the Ohio experiments, effects of defoliation on oil content were most pronounced at R3, and less consistent in 1996 than in 1997 (Table 4). In 1996, complete defoliation of the TC Blend and check hybrid at R3 reduced oil content 10 and 31%, respectively; in 1997, oil content was reduced 30 and 34%, respectively. Insufficient sample size and poor grain quality prevented oil and protein analysis of grain from the 100% defoliation treatment at VT in 1997. The Ohio results indicated that 100% defoliation as late as R5 could decrease oil content by 20%. Although the Illinois results showed that effects of 50% defoliation treatments on oil content were negligible (Table 3), the Ohio data indicated that 50% defoliation at R3 could reduce oil content by more than 10% (Table 4). These varying responses to defoliation for oil may be related to different TC Blend grain parents and pollinators used in each state.

In contrast to oil, 100% defoliation at VT/R1 and R3 increased protein content 68% and 59% in the Illinois study (Table 3). Defoliation effects on the protein content of grain from the TC Blend and check hybrid were similar in the Ohio study (Table 4). Complete defoliation at R3 and R5 increased protein content, averaged across year and corn type, by 57 and 18%, respectively.

For the Illinois data, the linear correlation coefficient was r = +0.92 between yield and oil, -0.73 between yield and protein, and -0.83 between oil and protein. In the Ohio study, linear correlations between yield and oil were similar for the HOC and the check hybrid each year. In 1996 and 1997, the linear correlation coefficient between yield and oil was +0.95 and +0.89 for HOC, and +0.95 and +0.88 for the check hybrid.

Results of the Ohio study suggest that decreases in grain yield and oil content due to defoliation during grain fill were closely related to decreases in kernel size as measured by 300 kernel weight (data not shown). Previous research on defoliation of corn hybrids (8,17) and inbreds (19) has reported similar effects of defoliation on kernel size. In 1997, kernel weight reductions resulting from complete defoliation at R3 and R5 were 55 and 38%, respectively (data not shown).

The defoliation effects on grain protein observed in this study may be similar to those that occur when drought stress conditions severely depress corn yields (6). Under such conditions, protein deposited early in the kernels is less diluted by starch deposited later during grain fill; consequently grain protein concentration increases. A similar explanation may account for the reduction in oil content associated with severe defoliation. Most of the oil in a corn kernel is in the embryo (11). The majority of embryo growth occurs during the third to fifth week after fertilization with maximum embryo size fixed by 6 weeks after pollination (9). Defoliation at R3, which occurs approximately 3 weeks after pollination, inhibits embryo growth and reduces oil accumulation. When defoliation is delayed until R5, more time for oil to accumulate in the embryo has occurred so the impact of defoliation on oil content is less severe.

Summary

This study evaluated effects of leaf removal on grain yield, and oil and protein content of HOC TC Blends across a range of soil types and weather conditions representative of the central Corn Belt. Effects of defoliation on the grain yield of TC Blends at various developmental stages were similar to the yield reductions reported for conventional corn hybrids. Grain yields decreased as leaf removal increased in severity and as time of defoliation neared VT. Complete defoliation reduced yields by 95% or more at VT/R1, and up to 70% at R3. Grain yield losses were generally larger than those predicted by the NCIA (13). Grain oil content was reduced as much as 30 to 40% with complete defoliation at V15/16, VT/R1, and R3, whereas protein content was increased as much as 50%. Effects of 25% and 50% leaf removal were mixed and often had no impact on yield, oil or protein content. In the Ohio study, two HOC TC Blends and a check hybrid showed similar responses to defoliation during grain fill for yield, and oil and protein content. For the Illinois data averaged over three years, the linear correlation coefficient was r = +0.92 between yield and oils, -0.73 between yield and protein, and -0.83 between oil and protein. However, since only a limited number of TC Blends were evaluated in this research, conclusions about the responses of HOC TC Blends to defoliation must be narrow. Since premiums for contract production of HOC are based on grain oil concentration, the lower oil content caused by severe defoliation may reduce or eliminate potential premiums.

Acknowledgments

We thank DuPont Specialty Grains and Pioneer Hi-Bred, a DuPont Company, for their support of the Ohio study, and for the numerous grain quality analyses provided. The financial support of the Illinois studies by the National Crop Insurance Services is gratefully acknowledged. We also acknowledge the generous donation of grain analysis services by Grand Prairie Cooperative elevator in Tolono, Illinois.

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