Changes in chemical and physical quality parameters of maize grain during three decades of yield improvement

Field Crops Research 59 (1998) 135±140

Changes in chemical and physical quality parameters of maize grain during three decades of yield improvement T.J. Vyn, M. Tollenaar* Crop Science Department, University of Guelph, Guelph, ON, Canada N1G 2W1 Received 24 February 1998; accepted 10 July 1998

Abstract Concern exists that the grain quality of maize (Zea mays L.) may decline due to breeding for increased yield. This study quanti®ed chemical- and physical-quality parameters of maize grain for hybrids representing three decades of grain yield improvement in Ontario, Canada. Six hybrids that were commercially important in Ontario from 1959 to 1988 were grown at two locations in southern Ontario during 1986 and 1987 at two plant densities. Grain contents of N, P, K, Ca, Mg, Zn, Cu, Mn, Se, lysine, tryptophan, and lipid were evaluated as chemical-quality parameters. Test weight, kernel density and weight, kernels exhibiting stress cracks, and breakage susceptibility were examined as indications of physical quality. Concentrations of Mg, Cu, Mn, and Se were greater in kernels of old hybrids than in more recent ones. Nitrogen concentration was greater in grain of recent hybrids and levels of N, P, and Mn all were lesser at high than at low plant density. Concentrations of lysine and tryptophan did not differ among hybrids. Differences in nutrient concentration were often greater among hybrids within an era than among means for eras of hybrid release. Among physical-quality traits, test weight, kernel density and kernel weight increased with more recent hybrids. These parameters were also higher with the lower plant density. Breakage susceptibility of kernels, although not affected by era of hybrid release, was less at low plant density. # 1998 Elsevier Science B.V. All rights reserved. Keywords: Maize (Zea mays L.); Genetic advance; Plant density; Grain physical traits; Grain chemical composition

1. Introduction The genetic improvement of maize grain yield has been substantial during the past three to ®ve decades (Duvick, 1992; Tollenaar et al., 1994) but questions have been raised about possible changes in grain quality associated with this improvement. It has been reported that the chemical quality of the grain varies among maize hybrids (Bullock et al., 1989). Cultivar differences in nutritional quality have also been observed for wheat (Triticum aestivum L.) and barley *Corresponding author. E-mail: [email protected] 0378-4290/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0378-4290(98)00114-2

(Hordeum vulgare L.) (Fuller et al., 1989). Physical grain quality also varies among maize hybrids. Hybrids vary for percent kernels exhibiting stress cracks (Vyn and Moes, 1988) and kernel breakage (Bauer and Carter, 1986; Vyn and Moes, 1988). Changes in grain chemical and physical quality for maize hybrids of different eras do not seem to have been reported. Grain quality in maize may be in¯uenced by growing conditions, in general, and plant density, in particular. It has been reported that kernel breakage is greater at high plant densities (Bauer and Carter, 1986; Moes and Vyn, 1988; Vyn and Moes, 1988). Improve-

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ment of grain yield in Ontario maize hybrids of approximately 1.5% per year during three decades from the late 1950s to the late 1980s appears to be associated with increased stress tolerance (Tollenaar et al., 1994). Differences in yield between old and new hybrids were greatest under marginal (i.e., low-yielding) conditions (Tollenaar, 1991) and grain yield was also affected more by weed interference in an old compared to a more recent hybrid (Tollenaar et al., 1997). Differences in grain quality characteristics among old and more recent hybrids could be associated with differences in stress tolerance among hybrids and may vary with the plant density at which maize is grown. The ®rst objective of this study was to assess chemical characteristics (concentrations of various nutrients and amino acids) and physical quality parameters (density and kernel breakage) of the grain of six selected maize hybrids representing three decades of breeding in Ontario. The second objective was to investigate the interaction (if any) in grain quality between two plant densities and the era of hybrid release. 2. Materials and methods Field experiments were carried out at the Elora Research Station (latitude 438250 N; altitude 380 m; soil-type Typic Hapludalf (USDA taraonomy); mean duration of growing season 2600 CHU (Crop Heat Units; Brown and Bootsma, 1993)) and the Woodstock Research Station (latitude 438080 N; altitude 317 m; soil-type Typic Hapludalf; mean duration of the growing season 2750 CHU). This study was part of a larger experiment (Tollenaar, 1989, 1991), but differed in some treatments and sampling procedures. 2.1. Cultural practices, treatments and plant material Maize was sown at the Elora Research Station on 7 May 1987 and 10 May 1988 and at the Woodstock Research Station on 5 May 1987 and 8 May 1988. The experiment was arranged in a split-plot design with plant density as main plots and maize hybrids as subplots with four replications. The hybrids were sown at a density exceeding 8 plants mÿ2 and, sub-

sequently, thinned at the seedling stage to obtain plant densities of 4 and 8 plants mÿ2. The hybrids tested were commercially important in central Ontario between 1959 and 1988. They included (with year of introduction in brackets): Pride 5 (1959), Warwick 263 (1961), PAG SX111 (1973) (Cargill Hybrid Seeds), Pioneer 3978 (1976) (Pioneer Hi-Bred), Pioneer 3851 (1983), and Pioneer 3902 (1988). Pride 5 and Warwick 263 are double-cross hybrids whose parents were produced by the University of Guelph and by the Northrup King company. The others were single-cross hybrids. For the purposes of this experiment, these hybrids were classi®ed as 1960s hybrids (Pride 5 and Warwick 263), 1970s hybrids (PAG SX111 and Pioneer 3978), and 1980s hybrids (Pioneer 3851 and Pioneer 3902). Subplots consisted of 12 rows each 6.1 m long, spaced 0.5 m apart. Suf®cient fertilizer was applied at both locations so that yield potential would not be limited by soil fertility: 150 kg N haÿ1, 22 kg P haÿ1 and 42 kg K haÿ1 were applied and incorporated prior to seeding. An additional 100 kg N haÿ1 were applied 6 weeks later. Complete weed control was obtained with herbicide application and hand weeding. Counter 15G [S-(((1,1 dimethylethyl)thio) methyl)0,0-diethyl phosphorodithioate] was applied for rootworm control. In 1988, plots at Elora were irrigated twice in early summer. 2.2. Sampling procedures At maturity, grain was hand-harvested at about 25% moisture content and shelled with a stationary sheller. The grain was dried at 308C in 1987 and at 608C in 1988 until a moisture content of 150 g kgÿ1 was reached. The difference in drying temperatures for the 2 years would not affect the chemical characteristics of the grain. Samples were then placed in a growth cabinet set at 238C and 72% relative humidity for 7 days to ensure that the maize equilibrated at approximately 150 g kgÿ1 moisture content. Broken kernels and foreign material were removed by sieving 300±400 g samples over 4.76 mm round-hole sieve. 2.3. Chemical-quality parameters Samples for chemical analyses were dried at 808C until a constant weight was reached. Within each year

T.J. Vyn, M. Tollenaar / Field Crops Research 59 (1998) 135±140

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and location, the four replications of each treatment were combined resulting in 2 years and two locations with four replications for statistical analysis. The dried grain of each hybrid was ground prior to analyses for concentrations of macronutrient elements N, P, K, Ca, and Mg, for micronutrient elements Zn, Cu, Mn, and Se (selected treatments only), for the amino acids lysine and tryptophan, and for lipid. Nitrogen concentration was determined colorimetrically with a Technicon Auto Analyzer II after digestion of 250 mg samples with sulphuric acid (Thomas et al., 1967). Inductively coupled plasma spectrometry was used for determination of P, K, Ca, Mg, Cu, Zn, and Mn in a nitric acid extract of the grain (Zarcinas et al., 1987). Selenium was determined using Hydride Generation Atomic Absorption Spectroscopy (Barrington Laboratories, Mississauga, Ont.). Lysine and tryptophan were analyzed with a reverse phase high-performance liquid chromatography (Heinrikson and Meredith, 1984). Lipid content was determined using the standard AOAC (1984) methodology.

on a light table, and categorized as having single, double, multiple, or no stress cracks according to criteria described by Thompson and Foster (1963). These categories were combined and reported as total stress cracks. Volumetric test weights were determined according to the method speci®ed by the Canadian Grain Commission (1980). For kernel density, 100 kernels were placed in a solution of 90% ethanol and 10% water and the volume displaced was recorded. Kernel weight was determined from a 200-kernel sample.

2.4. Physical-quality parameters

3.1.1. Macronutrients Hybrids differed for all the macronutrient elements except Ca (Table 1). The differences in P and K did not appear to be related to the era of hybrid release because their concentrations were similar for 1960s and 1980s hybrids. Mg concentration was greater in the 1960s hybrids than in later hybrids. N concentration at lower plant density was greater in 1980s hybrids than in earlier ones, but, differences in N

3. Results and discussion 3.1. Chemical quality The hybrid by plant density interaction was nonsigni®cant for all compounds analyzed except N and most results were averaged across densities (for hybrids) and across hybrids (for density).

Kernel breakage was determined by passing 200 g samples of grain through the Wisconsin Breakage Tester (Watson and Herum, 1986) and sieving as above. The weight of the material remaining on the sieve was used to calculate percent breakage (Watson and Herum, 1986). For stress-crack analysis, 100 unbroken kernels were selected at random, placed

Table 1 Effect of maize hybrids on grain concentration of P, K, Ca, Mg, Zn, Cu, Mn (averaged for two plant densities), and Se P

K

Ca

Mg

Zn

(%) Pride 5 (1960s) Warwick 263 (1960s) PAG SX111 (1970s) Pioneer 3978 (1970s) Pioneer 3851 (1980s) Pioneer 3902 (1980s) Contrasts 1960s vs. 1970s 1960s vs. 1980s 1970s vs. 1980s **, * a

0.29 0.30 0.27 0.25 0.29 0.28

Mn

Se

(mg kg ) a

ab a b c a a

0.37 0.37 0.34 0.37 0.39 0.37

**

*

NS

NS

**

Cu ÿ1

**

a a b a a a

0.021 0.019 0.019 0.016 0.020 0.021 NS NS NS

a a a a a a

0.093 0.091 0.088 0.079 0.089 0.086

a ab c d bc c

13.4 17.1 13.3 13.9 13.1 14.6

bc a b b b b

2.00 2.17 1.32 1.43 1.48 1.18

a a bc bc b c

3.97 4.56 4.12 2.88 3.10 3.41

**

*

**

**

*

*

**

**

*

NS

NS

NS

b a ab d cd c

, NS ± Significance at the 1%, 5%, and nonsignificant at the 5% level of probability, respectively. Within a column, data followed by the same letter do not differ significantly according to the protected LSD test (pˆ0.05).

0.012 0.010 0.018 0.010 0.004 0.008 NS NS *

ab bc a bc c bc

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Table 2 Effect of maize hybrids and plant density on grain concentration of N Hybrid

4 plants mÿ2 (%)

8 plants mÿ2 (%)

Significancea

Pride 5 (1960s) Warwick 263 (1960s) PAG SX111 (1970s) Pioneer 3978 (1970s) Pioneer 3851 (1980s) Pioneer 3902 (1980s)

1.44db 1.53 bc 1.60 b 1.51 cd 1.76 a 1.60 b

1.43 1.48 1.51 1.39 1.46 1.41

NS NS NS

NS

NS NS NS

Contrasts 1960s vs. 1970s 1960s vs. 1980s 1970s vs. 1980s

** **

ab ab a b ab ab

** * **

** * , , NS ± Significance at the 1%, 5%, and nonsignificant at the 5% level of probability, respectively. a Significance of differences between plant densities. b Within a column, data followed by the same letter do not differ significantly according to the protected LSD test (pˆ0.05).

concentration among hybrids were not signi®cant at the high plant density (Table 2). Among the macronutrients, only N and P concentrations were signi®cantly affected by plant density; concentrations were lower at the high than at the low density (Table 3). 3.1.2. Micronutrients Grain [Zn], [Cu], [Mn], and [Se] tended to be higher in 1960s maize hybrids than in later ones (Table 1). The 1960s hybrids had a higher Zn concentration than Table 3 Chemical quality of maize grain as influenced by plant density (averaged for maize hybrids over locations and years) Element

4 plants mÿ2

8 plants mÿ2

Significancea

N (%) P (%) K (%) Ca (%) Mg (%) Zn (mg kgÿ1) Cu (mg kgÿ1) Mn (mg kgÿ1) Fat (%) Lysine (%) Tryptophan (%)

1.57 0.29 0.37 0.020 0.089 15.1 1.56 4.03 3.61 0.18 0.072

1.45 0.27 0.36 0.019 0.086 13.4 1.64 3.31 3.59 0.19 0.075

*

*

*

NS NS NS NS NS *

NS NS NS

, NS ± Significance at the 5%, and nonsignificant at the 5% level of probability, respectively. a Significance of differences between plant densities.

later ones, but this result was almost solely due to a high level of Zn in Warwick 263. Watson and Ramstad (1987) reported [Zn] in maize grain ranging from 12 to 30 mg kgÿ1 with an average of 14 and values obtained in our study were close to this average. Concentrations of Cu and Mn were signi®cantly higher for 1960s hybrids than for 1970s and 1980s hybrids. Averages for Cu (4.0 mg kgÿ1) and Mn (5.0 mg kgÿ1) reported by Watson and Ramstad (1987) are slightly higher than those found in our study. Selenium concentration was lower for 1980s hybrids than for earlier ones (pˆ0.10) and was quite small compared to Watson and Ramstad's (Watson and Ramstad, 1987) report that [Se] in maize grain ranges from 0.01 to 1.0 mg kgÿ1. Except for [Mn], concentrations of minor elements were not affected by plant density (Table 3). 3.1.3. Amino acids and lipid Lysine and tryptophan concentrations did not differ among hybrids (data not shown) or plant densities (Table 3). Protein quality is an important factor when determining maize quality. Bullock et al. (1989) commented that the zein endosperm protein increases as protein concentration increases, lowering feed quality somewhat because zein has only trace amounts of the essential amino acids lysine and tryptophan. Fuller et al. (1989) found little change in amino acid composition due to cultivar in the protein of 19 winter wheat cultivars, 19 spring barley cultivars and 21 winter barley cultivars. Lipid concentrations ranged from 3.38% for Warwick 263 to 3.95% for Pride 5. Although maize hybrids differed in lipid percentage and 1980s hybrids yielded 46% higher than 1960s hybrids (Tollenaar, 1989), differences in lipid levels were not associated with the era of hybrid release (data not shown) or plant density (Table 3). In contrast, Watson and Ramstad (1987) reported that the lipid percentage declined as grain yield of hybrids in the Corn Belt increased. 3.2. Physical quality 3.2.1. Kernel test weight, density, and weight Mean kernel test weight of the 1960s hybrids (757 kg mÿ3) was lower than that of the 1970s and 1980s hybrids (772 kg mÿ3). In 1988, low plant density had a greater test weight than high plant density

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Table 4 Influence of hybrid and plant density on kernel weight and percent kernels exhibiting stress cracks in 1988 Treatment

Kernel weight (mg) 1987

Hybrid Pride 5 (1960s) Warwick 263 (1960s) PAG SX111 (1970s) Pioneer 3978 (1970s) Pioneer 3851 (1980s) Pioneer 3902 (1980s) Density 4 plants mÿ2 8 plants mÿ2 Contrasts 1960s vs. 1970s 1960s vs. 1980s 1970s vs. 1980s

278 320 344 290 325 355

ca b a c b a

Stress cracks 1988

1988

(%)

4 plants mÿ2

8 plants mÿ2

278 313 360 304 343 358

275 b 299 a 307 a 40 c 292 ab 305 a

38 34 44 44 33 35

Wb 40 a 37 a

E 43 a 32 b

NS NS

NS

d c a c b ab

341 a 297 b

326 a 286 b

**

**

**

**

**

**

**

b b a a b b

** **

** *

, , NS ± Significance at the 1%, 5%, and nonsignificant at the 5% level of probability, respectively. Within a column, data followed by the same letter do not differ significantly according to the protected LSD test (pˆ0.05). b W: Woodstock, E: Elora. a

(769 vs. 763 kg mÿ3), perhaps because of difference in precipitation. In 1987, rainfall was adequate and evenly spaced; in 1988, the spring was extremely dry and moisture stress would likely have been greater for high plant density. Kernel densities of the 1960s hybrids (1.22 g cmÿ3) were lower than those of the 1970s (1.26 g cmÿ3) and 1980s (1.25 g cmÿ3) at Woodstock, but hybrids did not differ at Elora (data not shown). Kernel density was greater at 4 than at 8 plants mÿ2 for both locations (1.26 vs. 1.23 g cmÿ3). Recent hybrids had the heaviest kernels with a few exceptions at 8 plants mÿ2 (Table 4). This increase in kernel weight could be a result of later senescence of leaves during the grain ®lling period (Tollenaar, 1991). In 1988, kernel weight was lower at high density for all but the 1960s hybrids (analysis not shown). The lower kernel weight for the 1970s and 1980s hybrids at 8 plants mÿ2 compared to 4 plants mÿ2 was associated with a 15±20% greater grain yield (Tollenaar, 1989). The same increase in plant density resulted in only a slight yield increase (8%) for Warwick 263 and no change in yield for Pride 5 (Tollenaar, 1989).

3.2.2. Stress cracks and breakage In 1988, the two 1970s hybrids had the largest number of cracked kernels (Table 4). Because the 1960s and 1980s hybrids did not differ, variation among hybrids does not seem to be related to era of release. Density by location interaction occurred due to more stress cracks at the low compared to high plant density at Elora (Table 4). In contrast, Vyn and Moes (1988) reported that stress cracking was not affected by plant density ranging from 5.5 to 7 plants mÿ2. Because only 1±5% of the kernels exhibited stress cracks in 1987, those results are not reported. The higher drying temperature in 1988 may be responsible for increase in stress cracking. A hybrid by density interaction for kernel breakage was apparent in 1987 at both locations and in 1988 at Elora. Kernel breakage was greater at high than at low density (18.2 vs. 15.1%; p<0.05) and differences among maize hybrids were greater at high than at low density. Pioneer 3902 was less susceptible to breakage than the other hybrids at high density and there were no consistent trends among the other ®ve hybrids (data not shown). Bauer and Carter (1986) and

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Vyn and Moes (1988) also reported differences in breakage among maize hybrids and greater breakage at high plant densities. Breakage was greater in 1988 than in 1987 (25.3% vs. 11.0%; p<0.05), which may be attributable to the higher drying temperature in 1988 (608C in 1988 vs. 308C in 1987). Vyn and Moes (1988) found that increased drying temperature was always accompanied by increased kernel breakage susceptibility. Breakage was generally greater for small kernels and was inversely related to kernel density only in 1988 at Elora (data not shown). 4. Conclusions Some reduction in chemical quality may have occurred with breeding for higher grain yield because Mg, Cu, Mn, and Se concentrations were higher in the 1960s hybrids than in later ones. According to Cullison and Lowrey (1987), these elements, with the exception of Se, are rarely lacking in feedstuffs commonly used for livestock. In addition, differences in nutrient concentration between hybrids within an era were frequently greater than differences among means of eras. Physical quality of grain appeared to have improved somewhat in recent hybrids. Test weight and kernel density (at one location) were higher for recent hybrids compared to the 1960s ones. Increasing plant density from 4 to 8 plants mÿ2 generally resulted in lower grain quality as test weight, kernel density and kernel weight decreased while breakage susceptibility increased. For chemical quality, only N, P, and Mn concentrations were adversely affected by the higher plant density. References AOAC, 1984. Official Methods of Analysis of the Association of Official Analytical Chemists, 14th ed. Association of Official Analytical Chemists, Arlington, VA. Bauer, P.J., Carter, P.R., 1986. Effect of seeding date, plant density, moisture availability, and soil nitrogen fertility on maize kernel breakage susceptibility. Crop Sci. 26, 1220±1226. Brown, D.M., Bootsma, A., 1993. Crop heat units for corn and other warm season crops in Ontario. Ont. Minist. Agric. Food

Factsheet, Agdex 111/31, ISSN no. 0225±7882. Ont. Minist. Agric. Food, Queen's Park, Ontario. Bullock, D.G., Raymer, P.L., Savage, S., 1989. Variation of protein and fat concentration among commercial corn hybrids grown in the southeastern USA. J. Prod Agric. 2, 157±161. Canadian Grain Commission, 1980. Grain Grading Handbook for Eastern Canada. Canadian Grain Commission, Winnipeg, Man. Cullison, A.E., Lowrey, R.S., 1987. Feeds and Feeding, 4th ed. Prentice-Hall, Englewood Cliffs, NJ. Duvick, D.N., 1992. Genetic contributions to advances in yield of US maize. Maydica 37, 69±79. Fuller, M.F., Cadenhead, A., Brown, D.S., Brewer, A.C., Carver, M., Robinson, R., 1989. Varietal differences in the nutritive value of cereal grains for pigs. J. Agric. Sci. 113, 149±163. Heinrikson, R.L., Meredith, S.C., 1984. Amino acid analysis by reverse-phase high-performance liquid chromatography: precolumn derivatization with phenylisothiocyanate. Anal. Biochem. 136, 65±74. Moes, J., Vyn, T.J., 1988. Management effects on kernel breakage susceptibility of early maturing corn hybrids. Agron. J. 80, 699±704. Thomas, R.L., Sheard, R.W., Moyer, J.R, 1967. Comparison of conventional and automated procedures for N, P and K analysis of plant material using a single digestion. Agron. J. 59, 240± 243. Thompson, R.A., Foster, G.H., 1963. Stress cracks and breakage in artificially dried corn. USDA Marketing Res. Rep. 631. US Govt. Print. Office, Washington, DC. Tollenaar, M., 1989. Genetic improvement in grain yield of commercial maize hybrids grown in Ontario from 1959 to 1988. Crop Sci. 29, 1365±1371. Tollenaar, M., 1991. Physiological basis of genetic improvement of maize hybrids in Ontario from 1959 to 1988. Crop Sci. 31, 119±124. Tollenaar, M., McCullough, D.E., Dwyer, L.M., 1994. Physiological basis of the genetic improvement of corn. In: Slafer, G.A. (Ed.), Genetic Improvement of Field Crops. Marcel Dekker, New York, pp. 183±236. Tollenaar, M., Aguilera, A., Nissanka, S.P., 1997. Grain yield is reduced more by weed interference in an old than in a new maize hybrid. Agron. J. 89, 239±246. Vyn, T.J., Moes, J., 1988. Breakage susceptibility of corn kernels in relation to crop management under long growing season conditions. Agron. J. 80, 915±920. Watson, S.A., Herum, F.L., 1986. Comparison of eight devices for measuring breakage susceptibility of shelled maize. Cereal Chem. 63, 139±142. Watson, S.A., Ramstad, P.E., 1987. Corn: Chemistry and Technology. Am. Assoc. Cereal Chemists, St. Paul, MN. Zarcinas, B.A., Cartwright, B., Spouncer, L.R., 1987. Nitric acid digestion and multi-element analysis of plant material by inductively coupled plasma spectrometry. Commun. Soil Sci. Plant Anal. 18, 131±146.