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Published in Agron J 100:414-420 (2008)
DOI: 10.2134/agrojnl2007.0166
© 2008 American Society of Agronomy
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WHEAT

White Wheat Grain Quality Changes with Genotype, Nitrogen Fertilization, and Water Stress

Carolina Saint Pierrea,b,*, C. James Petersona, Andrew S. Rossa, Jae-Bom Ohma,c, Mary C. Verhoevena, Mark Larsona and Bruce Hoefera

a Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331-3002
b current address: CIMMYT, Km 45 Carretera Mexico-Veracruz, Texcoco, 56130 México
c current address: USDA-ARS-RRVARC, Wheat Quality Lab., 214 Harris Hall, North Dakota State Univ., Fargo, ND 58105

* Corresponding author (c.saintpierre{at}cgiar.org).


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The production of hard white winter (HWW) wheats (Triticum aestivum L.) with acceptable protein content and quality over different environments requires the correct combination of genotypes and management practices. The objectives of this study were to evaluate moisture deficit and N management on grain protein and quality of seven HWW and two soft white winter (SWW) genotypes, and to identify genotypes and traits that minimize grain quality variability. Plots were irrigated during grain fill to replace from 100 to <30% of estimated evapotranspiration (ET). Biomass of three genotypes across the irrigation levels was used as an integrated estimation of plant water stress at late grain fill. Biomass reductions under water stress tended to be higher if plots received high N fertilization. Water stress reduced grain yield, test weight, and kernel weight and diameter. Reducing irrigation increased average grain protein content from 116.4 to 128.3 g kg–1. Nitrogen treatment did not affect grain yield. Additional N increased grain protein content and hardness for all genotypes. Reductions in test weight, and grain weight and diameter were observed under high N fertilization. High N fertilization would increase the numbers of kernels and extend the grain-fill period, which result in greater water and heat stress. The SWW genotypes had greater reductions in test weight than HWW genotypes with increasing water stress. Among HWW genotypes, late maturing genotypes had larger reductions in test weight than early genotypes. In regions where late season water stress is common, early maturing genotypes are more likely to produce consistent grain quality.

Abbreviations: DW, dry weight • ET, evapotranspiration • FW, fresh weight • HI, hardness index • HWW, hard white winter wheat • SKCS, single kernel characterization system • SWW, soft white winter wheat • TW, test weight


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
All rights reserved. No part of this periodical may be r eproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Received for publication May 17, 2007.
   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
WHEAT GRAIN QUALITY has been found to be determined by both genetics and environmental conditions (Peterson et al., 1992; Johansson et al., 2003). Kernel size and composition are mainly affected by environmental conditions which occur after anthesis and impact the rate and duration of grain fill (Dupont and Altenbach, 2003).

Water deficit, usually combined with heat stress, shortens the grain-filling period by accelerating leaf senescence. Reductions in the photosynthetic area caused by water stress limit the amount of assimilate available for grain filling (van Herwaarden et al., 1998a). This results in lower grain yields and higher protein concentrations (Lopez-Bellido et al., 1998). In contrast, both high yields and low grain protein contents are common in regions with relatively mild environmental conditions which favor long grain-filling periods. Panozzo and Eagles (1999) suggested that differences in grain composition are the result of changes in relative rates of carbohydrate and N accumulation induced by stress rather than differences in grain-filling duration. Under water deficit, high grain protein has been associated with low yield, and also with reduced test weight (TW) and kernel weight (Ozturk and Aydin, 2004). Late water deficit negatively affects the conversion of sucrose into starch but generally has less effect on protein deposition in the grain (Panozzo and Eagles, 1999). As a result, water stress can result in small, pinched kernels that are high in protein and low in flour yield.

Increasing N fertilizer and reducing irrigation are common strategies to increase grain protein concentration in spring wheat (Guttieri et al., 2005; van Herwaarden et al., 1998b) and winter wheat (Brown and Petrie, 2006). Increasing grain protein concentration with N fertilization has been more efficient in drier, low-yield areas since dilution of N with carbohydrates occurs in the grain when yields are high (Terman et al., 1969). In some cases, excessive N fertilization during vegetative stages may reduce yield and grain weight (Brown and Petrie, 2006; Nielsen and Halvorson, 1991).

Hard white wheat is the newest class of wheat in the United States, although not a new class of wheat for growers in Australia and the Middle East. It is distinctive because of its hard grain endosperm and white seed coat (bran). Hard white varieties with potential for both bread and noodle end-use applications have been developed, though understanding environmental effects on grain quality still represents a challenge (Souza et al., 2004; Guttieri et al., 2005).

A shift of large acreage of hard red and SWW to HWW production is being encouraged by Asian market demand and potential premiums for higher grain protein in hard wheat. Consistency in grain quality is a challenge for regions where yield potential is high and annual rainfall, soil fertility, and temperature stresses vary greatly. The transition to HWW would be facilitated with appropriate genotypes released together with management strategies that allow grain to meet protein concentration targets without sacrificing yield and grain quality (Guttieri et al., 2005; Habernicht et al., 2002; Souza et al., 2004).

The first objective of this study was to evaluate the main effects and interactions of moisture deficit and N management on HWW grain protein and grain quality properties such as TW, single kernel hardness index, and grain weight and diameter. The second objective was to compare genotype responses to water stress and N fertilization in terms of agronomic performance and grain quality. Understanding similarities or differences between genotype responses would help develop effective management strategies for specific grain end-use targets. Our ultimate goal was to identify genotypes and traits that minimize variability in grain quality that results from the diverse environments and the wide range of management practices used for wheat production.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Seven HWW and two SWW genotypes were grown under line source irrigation (Engel, 1991; Guttieri et al., 2000) over 2 yr. Genotypes included five Oregon State University breeding program experimental lines with varying high molecular weight glutenin compositions and quality characteristics: OR941048, OR850513–19, OR953475, OR942496, and OR943576 (Table 1 ). Other lines included NW97S277, a sib of the Nebraska cv. Antelope, and IDO591 (Manning/Karl's'), an experimental line from the University of Idaho with potential for use in both bread and noodle applications. Two regionally-adapted SWW genotypes, Stephens and Eltan, were also included in the study (Table 1). Stephens is a major SWW cultivar that has been grown in the region for more than 20 yr. Eltan is a unique SWW cultivar that performs well in bread and Asian noodle applications at higher grain protein levels. Eltan has been used as a check variety in HWW development by the USDA-ARS Western Wheat Quality Laboratory because it produces Asian noodles with superior color.


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  		Table 1. Genotype, identification class, origin, and Glu-locus composition for genotypes grown in Oregon State.

 
Plants were grown at two locations in Oregon during 2002–2003 and 2003–2004. Hermiston Agricultural Research and Extension Center (Hermiston) is located at 45°49' N, 119°17' W, and 185 m above sea level. Central Oregon Agricultural Research Center (Madras) is located at 44°40' N, 121°08' W, and 743.7 m above sea level. Hermiston station has deep, well drained, silt loam soils. Shallow, well drained, loam soils are common at Madras station. Average air temperature was 12.5°C for Hermiston and 9.9°C for Madras during 2002 to 2004. Total recorded annual precipitation levels at each location were 192 and 266 mm (Hermiston; 2002–2003 and 2003–2004, respectively), and 238 and 310 mm (Madras; 2002–2003 and 2003–2004, respectively).

Seed was planted in early fall (21 October at Hermiston 2002–2003; 8 October at Hermiston 2003–2004; 15 October at Madras 2002–2003; 24 September at Madras 2003–2004), in seven 0.15 m spaced rows using 110 kg seed ha–1. Plot size was 2.7 by 1.2 m. The nine wheat genotypes were planted as strips at 90° to the sprinkler line. Genotypes were randomized within four replications.

Plots were uniformly irrigated to replace 100% crop ET until 1 wk before anthesis. After that date, a central line-source sprinkler system was used to impose a continuous irrigation gradient. The water gradient was divided to represent four irrigation levels. Plots received 100 to 80% (treatment I3), 80 to 50% (treatment I2), 50 to 30% (treatment I1), and <30% (treatment I0) of measured ET replacement. Irrigation was scheduled using climatic data and ET estimates. Evapotranspiration was estimated by AgriMet, Pacific Northwest Cooperative Agricultural Weather Network, using the 1982 Kimberly-Penman ET model (Wright, 1982). Irrigation rates were confirmed by collecting water in cans placed throughout the gradient. The amount of water applied to fully irrigated plots was 200 and 190 mm at Hermiston in 2002–2003 and 2003–2004 respectively, and 380 and 480 mm at Madras in 2002–2003 and 2003–2004, respectively. Irrigation was continued until full canopy senescence. Alleys of 1 m between irrigation treatments were cut just before harvest to minimize border effects.

Two N treatments were imposed based on yield potential and desired grain protein level at full irrigation. All plots received a single fertilization of 170 kg N ha–1 (N1) in early March (Feekes 4). A blend of urea (46–0–0) and ammonium sulfate (21–0-0–24S) was used to provide 22.4 kg ha–1 of S. For the high N level (N2), there was a second application of 170 kg N ha–1 in May (Feekes 7), before the last uniform irrigation. For the N1 fertilization treatment, grain protein targets ranged from 90 to 130 g kg–1 from the drier to the fully irrigated plots. Under N2, grain protein targets ranged from 110 to 150 g kg–1 from the drier to the fully irrigated plots. Each N treatment had four field replications.

Days to heading and maturity were estimated from emergence date to 50% heading and total loss of green color, respectively. A 0.30 m section of row from each of six treatment combinations (N1I0, N1I1, N1I2, N2I0, N2I1, N2I2) in three genotypes (SWW: Stephens; HWW: IDO591 and OR943576) was hand-cut with a scythe. Samples were cut at ground level during late grain fill (contents of kernel soft but dry). Samples were oven dried at 70°C to constant weight. Aboveground dry matter was separated by hand into stems (stem + leaf sheath), leaves, and heads.

Plots were harvested with a small-plot combine in mid-July in Hermiston and in early August in Madras. There was no significant effect of lodging on grain yield in any treatment. After harvest, grain was cleaned and TW was determined following AACC Method 55–10 (American Association of Cereal Chemists, 2000). Values of kernel weight (mg), size (mm), hardness (hardness index, HI), and moisture content (g kg–1) were determined using the Single Kernel Characterization System (SKCS) model 4100 (Perten Instruments, Springfield, IL). For each sample, the SKCS integrated computer software (Perten Instruments, Springfield, IL) provided the means of 300 individual kernel determinations. The AACC method 55–31 was used for wheat single kernel hardness characterization.

Approximately 40 g of grain was ground in a cyclone mill to pass a 1 mm screen (UDY Corp., Fort Collins, CO). Protein concentration was measured by combustion (AACC 46–30 procedure) with a LECO FP-528 Nitrogen/Protein Determinator (Leco Corp., St. Joseph, MI). Grain crude protein (%) was calculated as %N detected by combustion times 5.7 (AACC 46–30 procedure). Raw protein data were corrected to 120 g kg–1 moisture basis using SKCS moisture values. The corrected grain protein was multiplied by 10 for unit conversion to g kg–1. Grain from Hermiston 2003–2004 was damaged by sprouting during storage; hence milling results from this environment are not reported.

A subsample of 600 g of grain from field replication 1 was combined with 600 g of grain from field replication 2 for milling purposes to increase the amount of flour obtained for each treatment and reduce the total sample number. The same procedure was followed with field replicates 3 and 4. Soft and hard wheats were milled on a Brabender Quadrumat Senior Mill (C.W. Brabender Instruments, South Hackensack, NJ) after tempering following a modified AACC 26–50 procedure. Roll temperature was kept constant at 31°C. Grain flow rate into the break rolls was adjusted to 130 to 135 g min–1 and 140 to 145 g min–1 for SWW and HWW genotypes, respectively. Bran, shorts, break flour, and reduced flour fractions were recovered after 16 min from the moment all grain passed through break rolls. Flour samples resulted from mixing break and reduction flour streams. Flour yield was calculated as the proportion of white flour to total recovered products. Grain from I0 was not included in the flour yield evaluation because of grain yield limitations.

The experimental design was a modified split plot, with four replications. Similar line-source irrigation designs were described by Engel (1991) and Guttieri et al. (2000). Data were analyzed by mixed effects analysis of variance using PROC MIXED in SAS (SAS Institute, 2001). Years and locations were combined as "environments" for the analysis (Geleta et al., 2002), thus each year–location combination represents a different environment. The effects of genotype, irrigation, N fertilization, and environment were considered fixed effects. Replications and the interactions with genotype, irrigation, N fertilization, and environment were considered random effects. Tests of significance for fixed effects and interactions of fixed effects were conducted by combining the appropriate linear combination of mean squares (Hanks et al., 1980; Johnson et al., 1983; McIntosh, 1983). Replications were considered nested within environments. The disadvantage of the system is that the irrigation levels were not randomized because of the systematic arrangement of the line-source sprinkle system. Limitations and statistical analysis of similar designs were discussed by Hanks et al. (1980) and Johnson et al. (1983).


   RESULTS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Biomass of three genotypes across the irrigation levels was used as an integrated estimate of plant water stress at late grain fill (Table 2 ). There were 13.5 and 17.5% biomass reductions at Hermiston in 2002–2003 and 2003–2004, respectively, and 43 and 30% biomass reductions at Madras in 2002–2003 and 2003–2004, respectively, when comparing the high with the low irrigated treatments. Decreased biomass of stems, leaves, and heads all contributed to the decrease in total biomass at lower irrigation levels.


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  		Table 2. Means for total biomass (g m–1), and stem, leaf, and head biomass (g m–1) at late grain fill in Hermiston and Madras during 2002–2003 and 2003–2004.

 
Irrigation had a significant effect on grain yield, grain protein, TW, and single kernel hardness, weight, and diameter (Tables 3 and 4 ). There was no significant difference on average grain yield when the replacement of ET was reduced from 100 to 80%. However, average grain yield was reduced by 16 and 19% when irrigation was 50 to 30% and <30% of ET replacement, respectively. Reducing irrigation from 100 to <30% of ET replacement increased average grain protein content from 116.4 to 128.3 g kg–1. The increase in grain protein was likely a function of yield reduction induced by water stress.


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  		Table 3. Mean squares from analysis of variance for grain yield (t ha–1), grain protein (g kg–1), test weight (kg hL–1), and grain hardness (HI), weight (mg), and diameter (mm) from Hermiston and Madras in 2002–2003 and 2003–2004.

 

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  		Table 4. Means and Duncan grouping for grain yield (t ha–1), grain protein (g kg–1), test weight (kg hl–1), grain hardness (HI), weight (mg) and diameter (mm), and flour yield at Hermiston and Madras nurseries in 2002–2003 and 2003–2004.

 
Average grain TW was reduced by 0.4, 1.5, and 2.5 kg hL–1 as water stress was gradually increased from 100–80 to 80–50%, 80–50 to 50–30%, and from 50–30 to <30%, respectively. Similarly, single kernel weight and diameter decreased as water stress increased. When comparing the highest and lowest irrigation levels (I3 and I0), there was a decrease of 16% in grain weight and 11% for grain diameter. Reductions in test weight, and grain weight and diameter due to water stress were greater under high than under lower N fertilization (Fig. 1 ). Average hardness index was positively correlated with grain protein and increased from 61 to 65 as water stress increased from the highest to lowest irrigation levels. Reductions of 23 g kg–1 were observed for flour yield as water stress increased.


Figure 1
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  		Fig. 1. Grain yield (t ha–1), grain protein (g kg–1), test weight (kg hL–1), and grain hardness (HI), weight (mg) and diameter (mm) for each N rate (N1 = 170 kg N ha–1; N2 = 170 + 170 kg N ha–1) and irrigation level [crop evapotranspiration replacement = 100 to 80% (I3), 80 to 50% (I2), 50 to 30% (I1), <30% (I0)]. Data from Hermiston and Madras nurseries in 2002–2003 and 2003–2004.

 
Averaged over locations, N rates did not affect total biomass or biomass of stems, leaves, and heads (Table 2). However, an increase in total biomass was observed at higher N treatments in Hermiston in 2003–2004. Biomass reductions under water stress tended to be higher if plots received high N fertilization.

Nitrogen fertilization had a significant effect on grain protein, TW, and grain hardness, weight, and diameter, but not on grain yield (Tables 3 and 4). No significant effect on grain yield was observed for interaction between fertilization x genotype or fertilization x irrigation. As expected, grain protein significantly increased with the second application of N. Averaged over irrigation treatments, protein increased from 106 to 141 g kg–1 at Hermiston in 2002–2003, 104 to 140 g kg–1 at Madras 2002–2003, and 89 to 122 g kg–1 at Hermiston in 2003–2004. Grain TW decreased from 77.2 to 75.9 kg hl–1 as N fertilization increased. This was associated with lower single kernel weight and diameter at higher N fertilization levels. Grain hardness was higher at the high N rate than at the N1 treatment. The N fertilization rate had no effect on total flour yield.

The responses in biomass accumulation were not different between genotypes. Averaged over treatments, the late maturing OR943576 showed reduced head biomass and higher leaf biomass when compared with earlier genotypes, such as Stephens. Yield ranged from 6.2 (Eltan, I0, N2) to 11.3 t ha–1 (Stephens, I2, N2) while grain protein varied from 100.3 (OR943576, I3, N1) to 152.2 g kg–1 (OR953475, I0, N2). HWW OR850513–19 had the highest total flour yield (65%) while Eltan, a SWW genotype, the lowest (60%).

Genotype x irrigation interactions were significant for grain yield, TW, and single kernel weight and diameter (Table 3). Grain yield increased in the nine varieties from I0 to I2. From I2 to I3, a yield increase was only observed in OR942496 while the other varieties had constant grain yield. The magnitude of TW reductions with water stress varied with the genotypes. IDO591 had the most stable TW across irrigation treatments. The two SWW genotypes, Eltan and Stephens, and the HWW OR943576, had larger TW reductions as water stress increased. HWW IDO591, OR953475, NW97S277, and OR850513–19 had lower reductions in both grain weight and diameter. Stephens, OR941048, OR942496, OR943576, and Eltan were more sensitive to water stress at both levels of N fertilization as indicated by reductions in grain weight and diameter.

Genotypes differed in their response to N rate for grain protein, test weight, and kernel hardness. Mean grain protein for HWW over treatments and environments ranged from 119.5 (OR941048) to 130.4 (OR953475) g kg–1 while SWW genotypes averaged 120.5 g kg–1 grain protein. A higher increase in protein with N fertilization was observed in HWW OR942496, NW97S277, OR953475, OR943576 than in SWW Stephens and Eltan. An average grain protein increase of 30 g kg–1 was observed in HWW OR942496, NW97S277, OR953475, and OR943576 as N fertilization increased. For SWW genotypes, average response to N fertilization was 26 g kg–1. HWW IDO591 and OR850513–19 had relatively more stable protein concentrations and TW across N treatments than the other genotypes. The two SWW genotypes Eltan and Stephens and the HWW OR943576 and OR942496, showed the largest reductions in TW as N fertilization increased. Grain hardness of HWW increased as protein levels increased with N fertilization. OR942496 and OR953475, however, showed less change in grain hardness as N fertilization increased.

A significant genotype by environment interaction was observed for grain yield, grain protein, TW, and kernel properties; however the ranking of genotypes over environments was not appreciably changed. Within each environment, there was a positive correlation (P < 0.001) between total plant biomass and grain yield, except for Hermiston 2003–2004 where the correlation was not significant (P = 0.08). The greater biomass production observed in Madras in 2003–2004 was not consistent across years and did not result in yield increases.


   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Irrigation and N fertilization contributed to variability in grain protein content and grain quality of HWW and SWW genotypes. Water stress reduced grain yield, TW, and kernel weight and diameter. Late N fertilization had no effect on grain yield. Nitrogen levels were not yield limiting, and the main effect of additional N was to increase grain protein content as also observed by Terman et al. (1969). Accordingly, grain protein of both HWW and SWW genotypes increased at higher N rates. Reductions in TW and grain weight and diameter, however, also were observed under high N fertilization. Reduced grain yield and weight were previously observed by Brown and Petrie (2006) under a fertilization rate of 336 kg N ha–1 in irrigated hard red winter wheats in an arid environment. López-Bellido et al. (1998) observed that N fertilization rate was inversely related to TW in a hard red spring genotype. Van Herwaarden et al. (1998a) reported lower levels of water-soluble carbohydrates available for translocation to developing grain under high N fertilization than under low N fertilization. In our study, the N2 fertilization treatment extended the grain fill period, which could have resulted in greater water and heat stress during late grain fill for plants under high N than under lower fertilization rates. This would also explain why reductions in grain physical quality due to high N fertilization were larger under water stress than under well irrigated conditions. Additionally, the high N rate increased the total kernel number, which tends to reduce kernel size, grain weights, and test weights (Sinclair and Jamieson, 2006).

The HWW genotypes differed in their response to irrigation as compared with the two SWW genotypes, Eltan and Stephens, which had greater reductions in TW than HWW genotypes as water stress increased. Stephens also had greater reductions in grain weight and diameter than the other genotypes as water stress increased. Among HWW genotypes, water stress caused greater TW reductions in late maturing genotypes as OR943576 and OR941048 than in early genotypes. Early maturing genotypes such as IDO591 and OR850513–19 had relatively more stable protein content, TW, and grain weight and diameter. Genotypes which flowered and matured earlier may have partially escaped late-season water stress. Similar findings were reported by Fischer and Maurer (1978). Earliness also allowed plants to escape heat stress, which in combination with water stress has been found to reduce grain quality (Stone et al., 1995; Wardlaw et al., 2002). Earliness would contribute to the ability of a genotype to produce consistently high grain quality, if there is a risk of late season water stress in the region.

Genotype by environment interactions were significant for most measured traits. Thus, conclusions regarding genotype ranking over all environments may not be valid for each particular combination of years and locations. However, genotype by environment interaction contributed a smaller proportion of variability than either genotype or environment main effects, as also observed by Peterson et al. (1998). Genotype ranks would be relatively consistent across environments since genotype by environment interaction mean squares are considerably smaller than environment and genotype mean squares (Fufa et al., 2005).

Increasing N fertilization has been previously identified as a better strategy than reducing irrigation for increasing both grain protein and noodle quality (Guttieri et al., 2005). They observed that late-season water stress reduced flour extraction rates and decreased the quality of Asian noodles. In their study, N fertilization did not affect milling yields and did not cause undesirable noodle discoloration. Rao et al. (1993) suggested early planting date as a strategy to reduce the impact of heat stress in wheat cultivars in the Pacific Northwest (USA). To avoid a negative impact on grain quality, our data suggest that water stress and/or heat stress should be minimized when N fertilization is used to achieve target protein levels.

Wheat cultivars with the ability to achieve high and consistent grain quality over a broad range of environmental conditions are preferable for the milling and baking industry. Even though significant genotype by treatment and genotype by environment interactions were observed, no significant crossover interactions were found. Genotypes superior in grain yield, protein, and quality generally ranked at the top within each management practice or environment. Selection for genotypes with high quality is critical to achieving improved HWW wheat cultivars.

All rights reserved. No part of this periodical may be r eproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 




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