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a North Dakota State Univ., Dickinson Res. Ext. Ctr., 1133 State Ave., Dickinson, ND 58601-3267
b Univ. Minnesota, Crookston Res. Ext. Ctr., 251 Owen Hall, 2900 Univ. Ave., Crookston, MN 56715-5001
c Univ. Minnesota, Dep. Agron. Plant Gen., 411 Borlaug Hall, St. Paul, MN 55108-6026
d North Dakota State Univ., Dep. Plant Sci., P.O. Box 5051, Fargo, ND 58105-5051
e North Dakota State Univ., Carrington Res. Ext. Ctr., P.O. Box 219, Carrington, ND 58421
* Corresponding author (pcarr{at}ndsuext.nodak.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: DM, dry matter
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Small-grain cultivar adaptation studies in the USA typically are located in environments where synthetic fertilizers and biocides are used. As a result, U.S. organic farmers generally grow modern cultivars that were not developed and selected in environments where organic production methods are used. Many of these farmers want access to modern cultivars developed and selected specifically in organic environments (D. Podoll, personal communication, 2005). However, such cultivars are not available. Some organic farmers grow cultivars developed before the widespread use of synthetic fertilizers and biocides because they believe that older cultivars are better adapted to organic environments than modern cultivars (B. Schmaltz, personal communication, 2005). These farmers believe that modern cultivars are not adapted to environments without using synthetic fertilizer and biocide inputs.
The performance of small-grain cultivars under organic management has been considered in countries outside the USA. Nine spring wheat cultivars were compared under conventional and organic management in Poland in 1989 and 1991 (Poutala et al., 1993). Synthetic fertilizer (100 kg N ha–1), herbicides, and fungicides were applied annually to plots under conventional management, whereas standards established by the International Federation of Organic Agriculture Movements (IFOAM, 2006) were followed in plots managed organically. Grain yield was reduced by 47 to 56% when cultivars were managed organically, and no differences among cultivars were detected. Two cultivars developed after 1979 produced more grain than cultivars developed before 1960 in plots managed conventionally. The researchers concluded that grain yield is equal or superior when modern high-yielding cultivars are grown compared with old cultivars in environments managed organically or conventionally.
Spring wheat cultivars were compared in two certified organic fields over a 2-yr period at Prince Edward Island, Canada (Nass et al., 2003). Grain yield was comparable in two of the four environments with the 10-yr average for Prince Edward Island, while less grain was produced in the other two environments. Yield for one of the cultivars was greater than another cultivar in one of the four environments, in contrast to the ranking of these two cultivars for yield in environments where synthetic agrichemicals were used. However, a similar change in rank between the two cultivars for yield was not detected in the other three environments. These results demonstrate the significant effect that environment can have on cultivar performance, but fail to reveal a consistent difference based on management system (e.g., conventional vs. organic).
Five spring wheat cultivars in 1997 and four in 1998 were compared in certified organic fields and neighboring fields where synthetic agrichemicals were used in the wheat belt region of southern Australia (Kitchen et al., 2003). Grain yield was higher in 11 of 14 paired comparisons in fields where synthetic chemicals were used, but in three instances more grain was produced when fields were managed organically. Interactions between cultivar and management system (conventional and organic) occurred, but the rank of the highest yielding cultivar was unchanged across the 14 paired comparisons. Results of this study suggest that management system can affect crop performance in a region, but not the ranking of adapted cultivars.
Evaluation of oat cultivars in certified organic fields has occurred in Minnesota since the early 1990s, and selection of breeding materials has been done in nurseries grown with minimal synthetic inputs (D.D. Stuthman, personal communication, 2005). A similar effort has not been undertaken with hard red spring wheat, even though this is the most widely grown small-grain crop in the northern Great Plains (USDA-NASS, 2006). While cultivar ranking has not been affected by management system in past research on spring wheat (Poutala et al., 1993; Kitchen et al., 2003; Nass et al., 2003), fewer than 10 cultivars were included in the comparisons and none occurred in regions similar climatically to the northern Great Plains. There is evidence that cultivar ranking for spring wheat is different in certified organic fields and in environments where synthetic agrichemicals are used, but Carr et al. (2003) indicated that results of these field experiments are not published.
There is a belief among some farmers that grain yield and quality parameters are superior for small-grain cultivars in environments managed organically when using seed lots produced with organic production methods compared with synthetic agrichemicals (B. Schmaltz, personal communication, 2005). Seed lots of a single cultivar can vary because of differences in production methods (McNeal and Berg, 1960), and these can have a profound impact on subsequent agronomic performance. For example, grain yield was enhanced from 5 to 10% when seed lots comprised of large compared with small kernels were used to establish spring wheat stands (Austenson and Walton, 1970; Spilde 1989). Similarly, seedlings were more vigorous when kernels contained greater amounts of protein compared with low protein kernels (Reiss and Everson, 1973). Grain yield and other agronomic traits may vary for the same cultivar when using a seed lot produced with organic practices and a seed lot with synthetic agrichemicals because of differences in nutrient availability and other factors, but comparisons between the two seed lot types have not been made.
The primary objectives of this study were to: (i) identify hard red spring wheat cultivars that are adapted to growing conditions in certified organic fields in Minnesota and North Dakota; and (ii) identify phenotypical growth traits that are correlated to yield performance in certified organic fields. A secondary objective was to determine if agronomic differences resulted consistently when using a seed lot produced with organic production practices and a seed lot produced with synthetic fertilizers and biocides.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The organic and conventional seed lots for Parshall were comprised of the same number of live kernels (98%) and were nearly identical in weight. In contrast, kernels were 20% heavier for the organic Stoa seed lot than the conventional seed lot. The organic seed lot for Stoa also contained more living kernels (99%) than the conventional seed lot (97%). Seeding rates took into account differences in kernel weights and live kernels between all treatments so identical numbers of living kernels were sown within each environment, although some differences in seeding rates across environments occurred (Table 2).
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Plant growth and development, susceptibility to disease infestations and weed competition were evaluated in cultivar plots. However, only grain yield, protein concentration, kernel weight, and volume weight were determined for treatments in all eight environments. Date when approximately 5% of seeded kernels had emerged as plants in each plot was recorded at Richardton both years, but not at other locations. Emerged plants were counted in a 2-m2 area in the center of each plot around 15 to 20 d after seeding at Richardton and at this same time from smaller areas within plots at other locations both years, except at Fullerton in 2004. Plants again were counted within the same area 5 to 10 d after initial numbers were counted only at Fertile in 2004 and at Richardton both years.
Plant vigor was assessed visually in each plot using a numerical rating (0 = poor vigor; 9 = good vigor) at 15 to 20 d after seeding in all environments except at Fullerton in 2004. Plant vigor was evaluated roughly 15 d later in plots at Fertile and Richardton in 2003, and at Comstock both years. A final assessment of plant vigor occurred approximately 5 d after the second evaluation at both Minnesota locations in 2003 but only at Comstock in 2004.
Plant height was determined when two leaves had emerged fully (Zadoks growth stage 12; Zadoks et al., 1974) by measuring the distance from the soil surface to the tip of the uppermost fully emerged leaf for 10 to 15 plants selected randomly in each plot in all environments except in 2004 at Fullerton. Likewise, height was measured when six leaves had emerged (Zadoks growth stage 16) at Comstock, Fertile, and Richardton in 2003. Plant height was determined from late anthesis through kernel development stages (Zadoks growth stages 69–87) by measuring the distance from the soil surface to the tip of the spike, excluding awns when present, in all environments except at Fullerton in 2004.
The number of days from seeding to emergence of the inflorescence (Zadoks growth stage 55) was recorded for plants in the center three rows of each plot only at Richardton in 2003 and 2004. The percentage of incident solar radiation intercepted by the crop canopy when plants had roughly six emerged leaves (Zadoks growth stage 16) was recorded as a visual estimate of the shaded to unshaded soil surface within each plot at these same two environments and both Minnesota locations in 2004. The amount of photosynthetically active radiation reaching the soil surface was determined around the time that emergence of the inflorescence was completed (Zadoks growth stage 59) using a Line Quantum Sensor (Spectrum Technologies, Inc., Plainfield, IL) at Richardton both years, following a procedure described by Carr et al. (1993).
Crop competition with weeds was assessed by comparing a visual estimate of the weed population within each plot to that in border areas separating adjacent plots where winter wheat had been spring seeded at Richardton both years. Aboveground weed biomass was clipped at the soil surface within a 0.5-m2 area in each plot, as was aboveground biomass of developing spring wheat plants. Harvested biomass was dried at 50°C for around 5 d and then weighed. Plant growth stages ranged from the emergence of the inflorescence just being completed to early kernel development (Zadoks growth stages 59–70) when weed populations and aboveground biomass production were assessed, depending on the cultivar.
The percentage of leaf surface discolored by suspected foliar pathogens was estimated visually by observing the overall condition of flag leaves among plants in each plot at Fertile in 2004. The presence or absence of leaf rust (Puccinia triticina Eriks.) on the flag leaf was assessed visually as the percentage of the flag leaf with rust pustules present. Disease pressure was not assessed in other environments, in part because disease symptoms were limited to less than 5% of the flag leaf surface. Likewise, lodging was minimal and not assessed in most environments, with the exceptions of Fertile in 2004, Fullerton in 2003, and Richardton both years. Lodging in these four environments was estimated for plants using a 0 to 9 scale (0 = all plants upright; 9 = all plants flat on the soil surface) when plants were at early stages of kernel development (Zadoks growth stages 70–77).
Spike density was determined by recording the number of spikes in a 1-m2 area in the center of each plot at the hard dough stage of kernel development (Zadoks growth stage 87) at Richardton, and from smaller areas within plots in the other environments at early stages of kernel development (Zadoks growth stages 70–77), except at Fullerton in 2004. A small-plot research combine was used to harvest grain from plots when grain was at the kernel hard stage of development (Zadoks growth stage 92) at all locations both years. Grain yields were reported on a 120 g kg–1 moisture basis. Grain kernel weight and grain volume weight were determined from subsamples. Grain protein concentration was determined for a subsample by near-infrared spectroscopy (Infratec grain analyzer, UAS Service Corp., Hawley, MN). Dockage was determined for a subsample using a Carter-Day Dockage Tester (Seedburo Equipment Co., Chicago, IL) only for grain harvested at Richardton in 2004.
Data were analyzed across all eight environments for grain yield, protein, kernel weight, and volume weight using the GLM procedure for balanced data from SAS (SAS Institute, 1985), since errors were homogeneous. The 19 cultivar treatments were considered fixed while environments and blocks were considered random effects. The environment x cultivar interaction was used to test cultivars, and residual error was used to test the environment x cultivar interaction. Comparisons of treatment means were done using an F-protected LSD (P < 0.05). Stepwise regression analyses were conducted with grain yield as the dependent variable within each environment for plant growth traits and other factors that were not evaluated across all eight environments. Only those independent variables that contributed to the model at P < 0.05 were included.
Stability of cultivars for grain yield was determined using the Cultivar Superiority (Performance) Measure (Lin and Binns, 1988) with the Agrobase 20 computer program (Agronomix Software, Inc., Winnipeg, MB). Stability values calculated using this method are the squares of the differences between an entry mean and the maximum mean at a location, summed and divided by twice the number of locations. Cultivars with the smallest stability values generally have larger yields and also are more stable than cultivars with larger values.
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RESULTS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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A consistent effect of seed lot (conventional and organic) on grain yield was not detected in this study. For example, higher grain yields resulted for Parshall when the organic seed lot was used at Fullerton in 2003, while more grain was produced when the conventional seed lot was sown at Comstock that year (Table 4). Grain yield differences were not detected between the two seed lots for Parshall in the other six environments. Likewise, grain yields were higher when the organic seed lot was sown for Stoa at Comstock in 2004 and Fullerton in 2003, while yield differences were not detected when conventional and organic seed lots were used in the other six environments.
A crossover in rank for grain protein concentration occurred for some cultivars in this study. For example, grain protein concentration was greater for ‘Coteau’ than other cultivars except Glupro at Comstock in 2004, while Glupro along with Alsen, BacUp, Dapps, and Ingot produced grain with a greater protein concentration than Coteau at Richardton that year (Table 5). The grain protein concentration was higher for Dapps than other cultivars except Glupro at Fertile in 2004, but was lower for Dapps than Glupro along with BacUp and Coteau at that location in 2003.
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Grain protein concentration was unaffected by seed lot selection in this study, with one exception. Grain protein concentration was greater when the conventional seed lot of Parshall was used compared with the organic seed lot at Comstock in 2003 (Table 5). Differences in grain protein concentration were not detected when using the two seed lots for Parshall in the other seven environments. Likewise, differences in grain protein concentration resulting from using the conventional and organic seed lots were not detected in any environment for Stoa.
Cultivars crossed over in rank for kernel weight across environments. Coteau produced heavier kernels than other cultivars except Chris at Fertile in 2003, while Chris along with Acadia, ‘Gunner’, and Walworth produced heavier kernels than Coteau at that location in 2004 (Table 6). Conversely, Chris produced heavier kernels than Gunner at Fullerton in 2004, while Gunner produced heavier kernels at Comstock that year. No single cultivar produced the heaviest kernels in each of the eight environments, but Chris tended to produce heavy kernels. Conversely, Dapps produced lighter kernels than at least four other cultivars in each environment.
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There was a crossover in ranking among cultivars for grain volume weight. Grain volume weight was heavier for BacUp than other cultivars except Ingot and Oklee at Fullerton in 2004, while it was heavier for those two cultivars along with Alsen than BacUp at Comstock that year (Table 7). Conversely, grain volume weight was heavier for Reeder than other cultivars except Oklee at Richardton in 2004, while grain volume weight was 27 to 60 kg m–3 heavier for Oklee than Reeder at Fullerton, depending on the year.
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Seed lot selection did not affect grain volume weight, except at Fertile and Richardton in 2004. Volume weight was heavier for grain produced when the conventional seed lot of Parshall was used compared with the organic seed lot in both environments (Table 7). Differences in grain volume weight were not detected between the two seed lots for Parshall in the other six environments, or Stoa in all environments.
Plant vigor at Zadoks growth stages 12 to 15 and plant height at Zadoks growth stage 16 explained 48% of the variation in grain yield at Comstock in 2003 (Table 8). However, spike density and other characteristics evaluated in this environment did not contribute significantly to the model. Plant height at Zadoks growth stage 16, spike density at Zadoks growth stages 70 to 87, and plant height at Zadoks growth stage 12 collectively explained 64% of the variation in grain yield at Fertile in 2003. However, plant height at Zadoks growth stages 70 to 77, spike density at Zadoks growth stages 70 to 87, and plant vigor at Zadoks growth stages 10 to 12 only explained 22% of the variation in grain yield at Comstock in 2004. Spike density at Zadoks growth stages 70 to 87 and plant vigor at Zadoks growth stages 10 to 12 explained 50% of the variation in grain yield at Fullerton in 2003. These results show that spike density, plant height, and plant vigor helped to explain the yield variation in several environments; yet, a large portion of the variation still was unexplained.
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Walworth had the lowest stability value (5) for grain yield across the eight environments of the 17 cultivars included in the study. Other modern cultivars having stability values of 20 or less included Ingot (12), Oklee (14), AC Cadillac (17), and Dapps (20). The remaining eight modern cultivars had stability values between 20 and 70, except for Coteau (118) and the two high-protein specialty cultivars, BacUp (103) and Glupro (181). By comparison, the four cultivars released before 1970 all had stability values greater than 70, including 71 for Waldron, 115 for Acadia, 132 for Red Fife, and 134 for Chris. These data indicate greater yield stability occurred for 10 modern cultivars compared with all four older cultivars in this study.
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DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Cultivars developed before 1970 generally were lower yielding than several modern cultivars in this study. The one exception occurred at Richardton in 2004 where drought stress reduced grain yield potential. Grain yield differences were not detected between two cultivars developed before 1960 and top performing modern cultivars in that environment, while yields for two cultivars developed in the 1960s were lower. Old cultivars never yielded more and sometimes less than top performing modern cultivars in other field studies under organic management (Poutala et al., 1993; Kitchen et al., 2003). Results of our research and these two previous studies do not support the hypothesis that old cultivars are better adapted to certified organic environments than modern cultivars if grain yield is an important selection criterion.
Past research demonstrated that old cultivars of winter wheat generally had higher grain protein concentration than modern cultivars in fields managed organically (Gooding et al., 1999). A similar relationship between the cultivar development era and ranking for grain protein concentration was not evident among the spring wheat cultivars included in our study. The grain protein concentration produced by the two oldest cultivars was among the lowest of any cultivar evaluated. Environments managed organically reportedly are lower in plant-available N compared with environments where synthetic N fertilizers are applied in Europe (Starling and Richards, 1990), but may not be in the northern Great Plains (Entz et al., 2001). Still, results of our study suggest that some modern hard red spring wheat cultivars may be preferred for grain protein concentration to old cultivars in certified organic environments.
A belief exists among many organic farmers in the northern Great Plains that modern small-grain cultivars generally are not adapted when first introduced into certified organic fields. Some of these growers suggest that progeny in subsequent generations become better adapted to the organic practices that are used (B. Schmaltz, personal communication, 2005). These observations suggest that natural selection may occur following the introduction of a cultivar into environments managed organically.
Natural adaptation can occur if heterogeneous populations are exposed and selection is made to contrasting management practices. A mixed population of genetically diverse winter wheat germplasm demonstrated natural adaptation for grain yield and biomass production when subpopulations were exposed to tilled and no-tilled seedbeds for several generations in the Pacific Northwest (Hwu and Allan, 1992). However, there is little likelihood that natural selection results following the introduction of most modern small-grain cultivars into environments managed organically because of genetic homogeneity in the populations (M.M. McMullen, personal communication, 2005). The genetic composition of wheat and other homozygous self-pollinated crops generally is maintained in most environments. Conditions that can affect homozygosity include an untimely frost or extreme heat that can sterilize the female part of the flower during pollination.
Seed lots produced using conventional and organic practices were included for two modern cultivars in our study. Evidence of natural selection occurring was unlikely for Parshall since the organic seed lot had been grown using certified organic practices for only 2 yr before beginning the study, and individuals comprising the population of this cultivar are genetically homogeneous. In contrast, there was a possibility that natural adaptation would be expressed in the conventional and organic seed lots of Stoa since both had been produced under the respective management schemes for more than 15 yr, and this cultivar is somewhat heterogeneous in genetic composition (S.S. Jones, personal communication, 2005). However, there was little evidence that natural selection occurred for either cultivar based on grain yield and quality comparisons between the two seed lots. Grain yield was comparable between organic and conventional seed lots in six of eight environments for both Parshall and Stoa, and grain protein concentration, kernel weight, and volume weight generally were similar. These results do not support the belief that modern small-grain cultivars become better adapted to production practices after being introduced into environments managed organically.
Agronomic comparisons between seed lots for the same cultivar can be confounded because of environmental differences. These differences can affect grain yield and other traits (Spilde, 1989). Admixtures also can result over time if more than one cultivar of the same crop is grown and a portion of the harvested grain is saved for seeding.
Several wheat cultivars had been grown at the locations where the organic and conventional seed lots of Parshall and Stoa were produced that were used in this study. However, electrophoresis analyses by the N.D. State Seed Department confirmed that cultivar integrity was preserved in the four seed lots that were used (J. Prischmann, personal communication, 2003). The two Parshall seed lots were nearly identical in live kernel numbers and weight, whereas the conventional seed lot of Stoa contained fewer living kernels that were 20% lighter in weight than the organic seed lot. Research by Spilde (1989) and others (Austenson and Walton, 1970) suggested that the lower yields could result when the conventional Stoa seed lot was used because kernels weighed less. Still, no differences in grain yield resulted when the conventional and organic seed lots for Stoa were used in six of the eight environments included in this study. These results suggest that seed lot type (conventional and organic) generally does not affect wheat cultivar performance in certified organic environments, although additional research is needed.
Various traits may be desirable for cultivars that are grown in environments managed organically. An ability to compete with weeds is one characteristic that has been identified (Poutala et al., 1993; Lammerts van Bueren et al., 2003). Weed growth suppression has been linked to plant stature, and Nass et al. (2003) suggested that tall cultivars may be more competitive because of a denser plant canopy and heightened ability to shade the soil surface. Early plant vigor and vegetative growth may enhance the ability of small-grain cultivars to compete with weeds (Richards and Heppel, 1990).
Several phenotypical growth traits relating to early crop growth and plant stature helped to explain the variation in grain yield in some of the environments in our study. However, the amount of variation explained was inconsistent. For example, early plant vigor was assessed at Zadoks growth stages 10 to 12 in seven environments but contributed to explaining variation in grain yield in only three environments. Plant stature was determined at the same time in the seven environments and contributed to explaining variation in yield in only one environment. Finally, plant height assessed at later growth stages contributed to explaining variation in grain yield in fewer than half of the environments. Cosser et al. (1997) reported little relationship between plant stature and grain yield or even an ability to suppress weed growth in some instances. Our data suggest that tallness may not be an important trait among cultivars adapted to environments managed organically because of the impact of the trait on weeds, particularly if grain yield is an important selection criterion.
Resistance to disease is a desirable quality for small-grain cultivars to possess in environments managed organically (Lammerts van Bueren et al., 2003). In our study, a lack of flag leaf discoloration resulting from suspected plant pathogens and leaf rust both helped to explain the variation in grain yield in the single environment where disease pressure was severe. Other traits relating to plant development, canopy closure, aboveground biomass production, and spike density were correlated with grain yield, but not consistently. These results suggest an inability of using the phenotypical growth traits evaluated in this study to predict reliably the performance of hard red spring wheat cultivars for yield in environments managed organically.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Caution should be used in applying results of this investigation to the ongoing debate regarding cultivar adaptation in environments managed organically. Cultivars developed in different eras were included in the study, but only two were developed before 1960, when synthetic agrichemicals began to be used commercially. Better representation of cultivars developed before 1960 along with modern cultivars may be warranted in future research to determine with certainty if unimproved heritage and other old cultivars are inferior to modern cultivars for grain yield and quality in environments managed organically.
Our results do not support the hypothesis that natural selection occurs in succeeding generations following the introduction of a modern cultivar into environments managed organically. However, natural selection may occur after an old landrace or other genetically heterogeneous population is introduced. Research should be considered which explores the possibility.
Beyond the scope of this investigation was determining if the need exists to develop and select small-grain cultivars in environments managed organically. Resources dedicated to develop and select small-grain cultivars are shrinking at public agricultural institutions, so an answer to this question is needed for the limited funds still available to have the greatest impact on commercial farmers. Research is needed that determines if distinct breeding programs are necessary to develop and select cultivars that are adapted to certified organic environments and environments where synthetic agrichemicals are used. If not, then resources could remain focused on developing and selecting cultivars in the dominant production system used by commercial farmers in a region.
This investigation failed to identify phenotypical growth traits and development traits that explained consistently the variation in grain yield. Additional work is needed to determine if phenotypical growth traits not considered in this investigation can be used to predict small-grain cultivar adaptation in certified organic environments, particularly if farmer–scientist cultivar breeding efforts continue to generate interest.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication March 16, 2006.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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from the analysis of variance for grain yield, crude protein, kernel weight, and test weight of 19 hard red spring wheat cultivar treatments in eight experiments (environments) over a 2-yr period in certified organic fields within Minnesota and North Dakota.