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• 21. [Article] Association between length of grain filling period and grain yield in two wheat populations (Triticum aestivum L. em Thell.)

  The objective of this study was to determine interrelationships among agronomic traits in early and late maturing populations. Two populations were obtained from the crosses, Roussalka/Tesopaco 76 and ...

  Citation × Citation Citation Abstract Copy Title: Association between length of grain filling period and grain yield in two wheat populations (Triticum aestivum L. em Thell.) Author: Min, Hwang Kee The objective of this study was to determine interrelationships among agronomic traits in early and late maturing populations. Two populations were obtained from the crosses, Roussalka/Tesopaco 76 and Yamhill/Aspen. Seeds were space planted with split plot design and nine agronomic traits were observed. In comparative studies between early and late populations, the early population was earlier in heading date, maturity date, longer maturity duration, heavier kernel weight, and higher harvest index. However, it was shorter in plant height, had fewer tillers, kernels and lower grain yield than the late population. Grain filling duration expressed positive relationships with grain yield in both crosses, although the correlation coefficient with grain yield was very low compared to other agronomic traits. Grain filling duration showed consistent positive relationships with kernel weight in both populations and with kernel number in the late population. No relationship was found between grain filling duration and tiller number. Grain filling duration influenced grain yield mainly by the indirect effects of kernel weight and kernel number. Yield components generally showed high positive relationships with grain yield; tiller number being the most important, followed by kernel number, and kernel weight. Competition among yield components was minimal in this space planted study. Heading date showed a negative association while plant height and harvest index expressed high positive relationships with grain yield. Title: Association between length of grain filling period and grain yield in two wheat populations (Triticum aestivum L. em Thell.) Author: Min, Hwang Kee The objective of this study was to determine interrelationships among agronomic traits in early and late maturing populations. Two populations were obtained from the crosses, Roussalka/Tesopaco 76 and Yamhill/Aspen. Seeds were space planted with split plot design and nine agronomic traits were observed. In comparative studies between early and late populations, the early population was earlier in heading date, maturity date, longer maturity duration, heavier kernel weight, and higher harvest index. However, it was shorter in plant height, had fewer tillers, kernels and lower grain yield than the late population. Grain filling duration expressed positive relationships with grain yield in both crosses, although the correlation coefficient with grain yield was very low compared to other agronomic traits. Grain filling duration showed consistent positive relationships with kernel weight in both populations and with kernel number in the late population. No relationship was found between grain filling duration and tiller number. Grain filling duration influenced grain yield mainly by the indirect effects of kernel weight and kernel number. Yield components generally showed high positive relationships with grain yield; tiller number being the most important, followed by kernel number, and kernel weight. Competition among yield components was minimal in this space planted study. Heading date showed a negative association while plant height and harvest index expressed high positive relationships with grain yield. Close

• 22. [Article] Multi-location analysis for the identification of quantitative trait loci underlying disease resistance against Cephalosporium gramineum and Puccinia striiformis f. sp. tritici by linkage mapping in wheat (Triticum aestivum L.)

  Wheat (Triticum aestivum L.) is one of the major crops produced in the U.S. Pacific Northwest, a region known for its wheat production for international export. Wheat production in the region is threatened ...

  Citation × Citation Citation Abstract Copy Title: Multi-location analysis for the identification of quantitative trait loci underlying disease resistance against Cephalosporium gramineum and Puccinia striiformis f. sp. tritici by linkage mapping in wheat (Triticum aestivum L.) Author: Vazquez, Maria Dolores Wheat (Triticum aestivum L.) is one of the major crops produced in the U.S. Pacific Northwest, a region known for its wheat production for international export. Wheat production in the region is threatened by diseases such as Cephalosporium stripe and stripe rust. Cephalosporium stripe is a vascular wilt disease of wheat caused by the persistent soil-borne fungus and suspected necrotrophic pathogen Cephalosporium gramineum Nisikado & Ikata, and is a recurring disease in many localities when susceptible cultivars are grown. Stripe rust, a foliar disease of wheat caused by the air-borne biotrophic fungus Puccinia striformis f. sp. tritici is a disease present in every region around the world where commercial wheat is grown. Attaining durable resistance to stripe rust would greatly benefit wheat producers in the region. Combining stripe rust resistance with resistance to other diseases, such as Cephalosporium stripe, is challenging. Wheat cultivars with high levels of resistance to several diseases are favorable candidates for genetic studies to determine the inheritance of resistance and facilitate the development of a method to genotypically select for disease resistance. Two populations of recombinant inbred lines were developed from 'Tubbs'/'NSA-98-0995' (TxN) and 'Einstein'/'Tubbs' (ExT) with population sizes of 271 and 259 F[subscript (5:6)], respectively. Tubbs is susceptible to stripe rust and Cephalosporium stripe while Einstein and NSA-98-0995 demonstrate moderate to high resistance to both diseases. Both populations were assessed across seven environments (combinations of locations and years) for stripe rust resistance under natural infection and four environments for Cephalosporium stripe resistance under artificial inoculation. The populations were mapped using diversity array technology (DArT) and simple sequence repeat (SSR) markers for quantitative trait loci (QTL) analysis. Results for Cephalosporium stripe resistance was quantitatively inherited with several QTL detected (>5), including some QTL in the same chromosome location in both populations. For stripe rust resistance, seven QTL were identified in the TxN population, suggesting quantitative resistance contributed by several minor genes. In the ExT population two QTL with major effects and with epistatic interactions between them were identified. One of them, a major QTL from Tubbs on chromosome 2AS that may be Yr17, was not expressed in the TxN population or in Tubbs, perhaps owing to suppressor(s). Expression of the 2AS QTL in the ExT population may be due to interaction with the QTL on chromosome 6AL from the resistant parent Einstein or to any other gene in the background of the population. QTL on chromosomes 2AS, 5AL, and 6BS were associated with resistance to both Cephalosporium stripe and stripe rust. These results highlight a complex set of interactions among major genes, minor genes, the presence of different stripe rust races, epistasis, genetic background, and possibly a suppressor of resistance. Results from this study are expected to assist in selecting molecular markers to genotypically select for resistance to these diseases, improving the chances of developing wheat cultivars with durable resistance to both diseases in the future. Title: Multi-location analysis for the identification of quantitative trait loci underlying disease resistance against Cephalosporium gramineum and Puccinia striiformis f. sp. tritici by linkage mapping in wheat (Triticum aestivum L.) Author: Vazquez, Maria Dolores Wheat (Triticum aestivum L.) is one of the major crops produced in the U.S. Pacific Northwest, a region known for its wheat production for international export. Wheat production in the region is threatened by diseases such as Cephalosporium stripe and stripe rust. Cephalosporium stripe is a vascular wilt disease of wheat caused by the persistent soil-borne fungus and suspected necrotrophic pathogen Cephalosporium gramineum Nisikado & Ikata, and is a recurring disease in many localities when susceptible cultivars are grown. Stripe rust, a foliar disease of wheat caused by the air-borne biotrophic fungus Puccinia striformis f. sp. tritici is a disease present in every region around the world where commercial wheat is grown. Attaining durable resistance to stripe rust would greatly benefit wheat producers in the region. Combining stripe rust resistance with resistance to other diseases, such as Cephalosporium stripe, is challenging. Wheat cultivars with high levels of resistance to several diseases are favorable candidates for genetic studies to determine the inheritance of resistance and facilitate the development of a method to genotypically select for disease resistance. Two populations of recombinant inbred lines were developed from 'Tubbs'/'NSA-98-0995' (TxN) and 'Einstein'/'Tubbs' (ExT) with population sizes of 271 and 259 F[subscript (5:6)], respectively. Tubbs is susceptible to stripe rust and Cephalosporium stripe while Einstein and NSA-98-0995 demonstrate moderate to high resistance to both diseases. Both populations were assessed across seven environments (combinations of locations and years) for stripe rust resistance under natural infection and four environments for Cephalosporium stripe resistance under artificial inoculation. The populations were mapped using diversity array technology (DArT) and simple sequence repeat (SSR) markers for quantitative trait loci (QTL) analysis. Results for Cephalosporium stripe resistance was quantitatively inherited with several QTL detected (>5), including some QTL in the same chromosome location in both populations. For stripe rust resistance, seven QTL were identified in the TxN population, suggesting quantitative resistance contributed by several minor genes. In the ExT population two QTL with major effects and with epistatic interactions between them were identified. One of them, a major QTL from Tubbs on chromosome 2AS that may be Yr17, was not expressed in the TxN population or in Tubbs, perhaps owing to suppressor(s). Expression of the 2AS QTL in the ExT population may be due to interaction with the QTL on chromosome 6AL from the resistant parent Einstein or to any other gene in the background of the population. QTL on chromosomes 2AS, 5AL, and 6BS were associated with resistance to both Cephalosporium stripe and stripe rust. These results highlight a complex set of interactions among major genes, minor genes, the presence of different stripe rust races, epistasis, genetic background, and possibly a suppressor of resistance. Results from this study are expected to assist in selecting molecular markers to genotypically select for resistance to these diseases, improving the chances of developing wheat cultivars with durable resistance to both diseases in the future. Close

• 23. [Article] Combining ability and gene action estimates and the association of the components of yield in winter wheat crosses

  A diallel cross consisting of ten parents was grown on the Hyslop Agronomy Farm near Corvallis, Oregon, in order to obtain estimates of the gene action contributing to yield and its components in wheat. ...

  Citation × Citation Citation Abstract Copy Title: Combining ability and gene action estimates and the association of the components of yield in winter wheat crosses Author: Kronstad, Warren E. (Warren Ervind), 1932- A diallel cross consisting of ten parents was grown on the Hyslop Agronomy Farm near Corvallis, Oregon, in order to obtain estimates of the gene action contributing to yield and its components in wheat. Gene action estimates were obtained by two methods of diallel analysis and from narrow sense heritability values calculated by parent-progeny regressions involving both parental and F[subscript 1] data. In addition, path-coefficient analysis was utilized to investigate the direct and indirect associations of five variables on yield. The morphological characters measured were: (1) total yield per plant, (2) weight per kernel, (3) number of kernels per spikelet, (4) number of spikelets per spike, (5) number of spikes per plant and, (6) plant height. A large portion of the total genetic variation associated with the yield components, weight per kernel, kernels per spikelet, spikelets per spike and spikes per plant was the result of additive gene action. When the five variables were considered in terms of their associations with yield it was observed that weight per kernel, number of kernels per spikelet and the number of spikelets per spike mainly exerted direct effects on yield. The number of spikes per plant had no direct effect, but an indirect effect on yield through the other variables. A similar indirect association was noted for plant height. The data obtained from the path-coefficient analysis indicated further that the number of kernels per spikelet had the greatest direct effect on yield. Results obtained with correlation coefficients suggested that a negative association exists between weight per kernel and kernels per spikelet. Also such a negative association was found between the number of spikes per plant with weight per kernel and kernels per spikelet. These results would suggest the possible existence of a biological limitation between several of the components of yield. The diallel cross analysis for general and specific combining ability gave similar estimates of gene action when they were compared to narrow sense heritability values. However, when the Jinks-Hayman method was compared with the other two methods of estimating gene action, several discrepancies were observed. This lack of agreement was possibly due to the inability of this experimental material to meet one or all of the genetic assumptions required by the Jinks-Hayman method. The results of this study indicate that a breeding program with emphasis on increases in yield which considers each of the components separately, or in combination of two or more would offer the most promise. By this procedure the breeder could take advantage of the large amount of additive genetic variance associated with each of the components and at the same time, take into consideration any biological limitations which may exist. In utilizing the information obtained in this study in such a breeding procedure the plant breeder would be able to better evaluate the methods for selecting the best parents to be hybridized and in selecting the best lines from hybrid progeny. Title: Combining ability and gene action estimates and the association of the components of yield in winter wheat crosses Author: Kronstad, Warren E. (Warren Ervind), 1932- A diallel cross consisting of ten parents was grown on the Hyslop Agronomy Farm near Corvallis, Oregon, in order to obtain estimates of the gene action contributing to yield and its components in wheat. Gene action estimates were obtained by two methods of diallel analysis and from narrow sense heritability values calculated by parent-progeny regressions involving both parental and F[subscript 1] data. In addition, path-coefficient analysis was utilized to investigate the direct and indirect associations of five variables on yield. The morphological characters measured were: (1) total yield per plant, (2) weight per kernel, (3) number of kernels per spikelet, (4) number of spikelets per spike, (5) number of spikes per plant and, (6) plant height. A large portion of the total genetic variation associated with the yield components, weight per kernel, kernels per spikelet, spikelets per spike and spikes per plant was the result of additive gene action. When the five variables were considered in terms of their associations with yield it was observed that weight per kernel, number of kernels per spikelet and the number of spikelets per spike mainly exerted direct effects on yield. The number of spikes per plant had no direct effect, but an indirect effect on yield through the other variables. A similar indirect association was noted for plant height. The data obtained from the path-coefficient analysis indicated further that the number of kernels per spikelet had the greatest direct effect on yield. Results obtained with correlation coefficients suggested that a negative association exists between weight per kernel and kernels per spikelet. Also such a negative association was found between the number of spikes per plant with weight per kernel and kernels per spikelet. These results would suggest the possible existence of a biological limitation between several of the components of yield. The diallel cross analysis for general and specific combining ability gave similar estimates of gene action when they were compared to narrow sense heritability values. However, when the Jinks-Hayman method was compared with the other two methods of estimating gene action, several discrepancies were observed. This lack of agreement was possibly due to the inability of this experimental material to meet one or all of the genetic assumptions required by the Jinks-Hayman method. The results of this study indicate that a breeding program with emphasis on increases in yield which considers each of the components separately, or in combination of two or more would offer the most promise. By this procedure the breeder could take advantage of the large amount of additive genetic variance associated with each of the components and at the same time, take into consideration any biological limitations which may exist. In utilizing the information obtained in this study in such a breeding procedure the plant breeder would be able to better evaluate the methods for selecting the best parents to be hybridized and in selecting the best lines from hybrid progeny. Close

• 24. [Article] Oxidative gelation and functionality of wheat flour : effects of grain storage, flour aging, and grain type (hard or soft)

  This study examined changes in flour functionality during storage of grain and subsequent aging of flour milled from the grain. Freshly harvested grain was stored for 24 weeks and flour milled from the ...

  Citation × Citation Citation Abstract Copy Title: Oxidative gelation and functionality of wheat flour : effects of grain storage, flour aging, and grain type (hard or soft) Author: Mattson, Jacob E. This study examined changes in flour functionality during storage of grain and subsequent aging of flour milled from the grain. Freshly harvested grain was stored for 24 weeks and flour milled from the grain at specified time intervals after harvest (0, 3, 6, 12, and 24 weeks). For each milling date flour functionality was measured on the day of milling (day 0) and at specified intervals after milling (1, 3, 6, 13, 27, and 62 days). Storage and aging were conducted at 23 ± 1°C. The functional properties examined were flour absorption characteristics, quantified using the solvent retention capacity (SRC) test, and oxidative gelation capacity (OGC), which was measured viscometrically, using a Rapid Visco Analyzer (RVA). SRC measures absorption capacity of flour emphasizing different flour polymers in each of the four solvents (water, all polymers: sucrose, arabinoxylans (AX) and gliadins: sodium carbonate, damaged starch: lactic acid, glutenins). Oxidative gelation is a process whereupon a weak gel is formed in a hydrated flour system under oxidative conditions and is thought to be largely a function of the reactivity of ferulic acid residues esterified to AX, although proteins are also involved. To determine if oxidation of flour lipids might accompany changes in OGC, the concentration of malondialdehyde (MDA), a lipid oxidation byproduct, was measured. Four soft-wheat varieties with divergent functionalities were selected to examine the effects of storage and aging. Additionally, a survey was conducted to examine the range of OGC in a selection of hard-grained wheat varieties from the Oregon State University wheat-breeding program. From this survey, one variety with high and one variety with low OGC were selected for a pilot study to determine the effect of hydrogen peroxide and azodicarbonamide (ADA) concentrations on OGC in straight grade flour. Variety was the strongest factor in determining flour functionality expressed as SRC and OGC. This is unsurprising, because varieties were chosen based on differences in absorption characteristics and OGC as indicated by preliminary testing. In contrast, variety was the weakest factor in determining changes in MDA concentration. As a function of grain storage time, water, sucrose and sodium carbonate SRC values increased. In contrast, lactic acid SRC values declined. Although many of these changes were statistically significant, their functional significance remains unclear. As a function of grain storage time, OGC initially increased to week 3 then declined to week 24. Not only was this change statistically significant, but the magnitude of the change could be considered functionally significant. Because OGC is a trait that currently only has theoretical value in food processing (i.e. OGC is not a trait currently taken into consideration during food processing), it is difficult to definitively conclude what constitutes functional significance. Grain storage time had the strongest influence on changes in MDA concentration. The trend of changes in MDA concentration was similar to that observed for OGC. Flour age was the weakest contributor to changes in SRC. Looking at individual SRC solvents, flour aging time did not significantly influence changes in water SRC values. However, as flour aged, sucrose SRC values significantly increased and sodium carbonate and lactic acid SRC values decreased. Although changes in sucrose, sodium carbonate, and lactic acid SRCs were statistically significant, their functional significance was again unclear. As a function of flour age, OGC increased. As a function of flour age, MDA concentration initially increased, but subsequently declined and remained constant from day 6 to day 62. Each variety appeared to show a different relationship between peroxide peak viscosity (PPV) and peroxide peak breakdown viscosity (PPBV). Proportional PPBV also appeared to differ between varieties, and the relationships (PPBV% vs PPV) were nonlinear. This suggested that there was a maximum PPV for each variety at which PPBV no longer increased. Data suggest qualitative differences in the gels formed in each variety that require further investigation. Speculation allows the idea that the RVA method used here could provide a way of expressing functional differences in OGC that might relate to structure differences in AX. Title: Oxidative gelation and functionality of wheat flour : effects of grain storage, flour aging, and grain type (hard or soft) Author: Mattson, Jacob E. This study examined changes in flour functionality during storage of grain and subsequent aging of flour milled from the grain. Freshly harvested grain was stored for 24 weeks and flour milled from the grain at specified time intervals after harvest (0, 3, 6, 12, and 24 weeks). For each milling date flour functionality was measured on the day of milling (day 0) and at specified intervals after milling (1, 3, 6, 13, 27, and 62 days). Storage and aging were conducted at 23 ± 1°C. The functional properties examined were flour absorption characteristics, quantified using the solvent retention capacity (SRC) test, and oxidative gelation capacity (OGC), which was measured viscometrically, using a Rapid Visco Analyzer (RVA). SRC measures absorption capacity of flour emphasizing different flour polymers in each of the four solvents (water, all polymers: sucrose, arabinoxylans (AX) and gliadins: sodium carbonate, damaged starch: lactic acid, glutenins). Oxidative gelation is a process whereupon a weak gel is formed in a hydrated flour system under oxidative conditions and is thought to be largely a function of the reactivity of ferulic acid residues esterified to AX, although proteins are also involved. To determine if oxidation of flour lipids might accompany changes in OGC, the concentration of malondialdehyde (MDA), a lipid oxidation byproduct, was measured. Four soft-wheat varieties with divergent functionalities were selected to examine the effects of storage and aging. Additionally, a survey was conducted to examine the range of OGC in a selection of hard-grained wheat varieties from the Oregon State University wheat-breeding program. From this survey, one variety with high and one variety with low OGC were selected for a pilot study to determine the effect of hydrogen peroxide and azodicarbonamide (ADA) concentrations on OGC in straight grade flour. Variety was the strongest factor in determining flour functionality expressed as SRC and OGC. This is unsurprising, because varieties were chosen based on differences in absorption characteristics and OGC as indicated by preliminary testing. In contrast, variety was the weakest factor in determining changes in MDA concentration. As a function of grain storage time, water, sucrose and sodium carbonate SRC values increased. In contrast, lactic acid SRC values declined. Although many of these changes were statistically significant, their functional significance remains unclear. As a function of grain storage time, OGC initially increased to week 3 then declined to week 24. Not only was this change statistically significant, but the magnitude of the change could be considered functionally significant. Because OGC is a trait that currently only has theoretical value in food processing (i.e. OGC is not a trait currently taken into consideration during food processing), it is difficult to definitively conclude what constitutes functional significance. Grain storage time had the strongest influence on changes in MDA concentration. The trend of changes in MDA concentration was similar to that observed for OGC. Flour age was the weakest contributor to changes in SRC. Looking at individual SRC solvents, flour aging time did not significantly influence changes in water SRC values. However, as flour aged, sucrose SRC values significantly increased and sodium carbonate and lactic acid SRC values decreased. Although changes in sucrose, sodium carbonate, and lactic acid SRCs were statistically significant, their functional significance was again unclear. As a function of flour age, OGC increased. As a function of flour age, MDA concentration initially increased, but subsequently declined and remained constant from day 6 to day 62. Each variety appeared to show a different relationship between peroxide peak viscosity (PPV) and peroxide peak breakdown viscosity (PPBV). Proportional PPBV also appeared to differ between varieties, and the relationships (PPBV% vs PPV) were nonlinear. This suggested that there was a maximum PPV for each variety at which PPBV no longer increased. Data suggest qualitative differences in the gels formed in each variety that require further investigation. Speculation allows the idea that the RVA method used here could provide a way of expressing functional differences in OGC that might relate to structure differences in AX. Close

• 25. [Article] A study of methods of parental evaluation using testers to predict subsequent progeny performance in winter wheat (Triticum aestivum L.)

  The major objective of this study was to determine why certain winter wheat cultivars, when hybridized, will produce a greater proportion of desirable plants in subsequent, segregating generations. Three ...

  Citation × Citation Citation Abstract Copy Title: A study of methods of parental evaluation using testers to predict subsequent progeny performance in winter wheat (Triticum aestivum L.) Author: Alexander, William Larry The major objective of this study was to determine why certain winter wheat cultivars, when hybridized, will produce a greater proportion of desirable plants in subsequent, segregating generations. Three winter wheat parents were chosen as the experimental material, based on their known performance as parents. Yamhill and Pullman Selection 101 are recognized as cultivars with good combining abilities for grain yield. Crosses with Nugaines have been disappointing, even though the cultivar itself is high yielding. Each parent was crossed to a series of five testers. These testers were chosen on the basis of their genetic diversity, especially for the components of yield. This parent x tester crossing scheme was analyzed as a 3 x 5 factorial, where the main effects due to parents and testers were their general combining ability effect estimates. The interactions of these main effects were their specific combining abilities. F₁ hybrids were evaluated for two years and F₂ populations for one year to characterize the parents' capacity to transmit selected attributes to their resulting progeny. These generations were evaluated on a per plant basis for their grain yields and the primary components of yield, tillers per plant, kernels per spike, and 1000 kernel weight. The four methods of evaluating parents assessed were parental performance, midparent-progeny correlations, examination of individual crosses, and combining ability analysis. Midparent-progeny correlations usually were not significant within the progeny of each parent. Significant differences were not found for grain yields among the parents in either year. However, significant differences existed for their expressions of yield components. Parental expressions of the yield components were generally more erratic than those of their F₁ progenies. Significant differences occurred for estimates of general combining ability effects in both years and for each generation in all traits. These estimates for a particular parent were relatively consistent. Specific combining ability was not found to be a dependable means of identifying superior combinations. Associations between the parental general combining ability effect estimates for kernels per spike and 1000 kernel weight were positive. Relationships between other yield component combinations were negative with regard to general combining ability effects. Trends observed in single crosses reflected the relative general combining abilities of the parents. Crosses involving Yamhill generally had fewer tillers with a higher number of kernels per spike, heavier kernel weights, and superior grain yields to those of the other parents. Progeny of Pullman Selection 101 were usually high in tillering, intermediate for number of kernels per spike, low in kernel weights, and intermediate for grain yields. The progeny of Nugaines were characterized by high tillering, a low number of kernels per spike, low kernel weights, and also low grain yields. The parent x tester crossing scheme was found to be an effective way of determining the potentials of the three parents by estimating their general combining abilities, as well as minimizing the number of crosses required. If, as found in this study, the general combining ability effect estimates of the parents for grain yield accurately predict performance of later generations, this parent x tester crossing scheme would be an efficient method of assessing the potentials of prospective parents in breeding programs. Title: A study of methods of parental evaluation using testers to predict subsequent progeny performance in winter wheat (Triticum aestivum L.) Author: Alexander, William Larry The major objective of this study was to determine why certain winter wheat cultivars, when hybridized, will produce a greater proportion of desirable plants in subsequent, segregating generations. Three winter wheat parents were chosen as the experimental material, based on their known performance as parents. Yamhill and Pullman Selection 101 are recognized as cultivars with good combining abilities for grain yield. Crosses with Nugaines have been disappointing, even though the cultivar itself is high yielding. Each parent was crossed to a series of five testers. These testers were chosen on the basis of their genetic diversity, especially for the components of yield. This parent x tester crossing scheme was analyzed as a 3 x 5 factorial, where the main effects due to parents and testers were their general combining ability effect estimates. The interactions of these main effects were their specific combining abilities. F₁ hybrids were evaluated for two years and F₂ populations for one year to characterize the parents' capacity to transmit selected attributes to their resulting progeny. These generations were evaluated on a per plant basis for their grain yields and the primary components of yield, tillers per plant, kernels per spike, and 1000 kernel weight. The four methods of evaluating parents assessed were parental performance, midparent-progeny correlations, examination of individual crosses, and combining ability analysis. Midparent-progeny correlations usually were not significant within the progeny of each parent. Significant differences were not found for grain yields among the parents in either year. However, significant differences existed for their expressions of yield components. Parental expressions of the yield components were generally more erratic than those of their F₁ progenies. Significant differences occurred for estimates of general combining ability effects in both years and for each generation in all traits. These estimates for a particular parent were relatively consistent. Specific combining ability was not found to be a dependable means of identifying superior combinations. Associations between the parental general combining ability effect estimates for kernels per spike and 1000 kernel weight were positive. Relationships between other yield component combinations were negative with regard to general combining ability effects. Trends observed in single crosses reflected the relative general combining abilities of the parents. Crosses involving Yamhill generally had fewer tillers with a higher number of kernels per spike, heavier kernel weights, and superior grain yields to those of the other parents. Progeny of Pullman Selection 101 were usually high in tillering, intermediate for number of kernels per spike, low in kernel weights, and intermediate for grain yields. The progeny of Nugaines were characterized by high tillering, a low number of kernels per spike, low kernel weights, and also low grain yields. The parent x tester crossing scheme was found to be an effective way of determining the potentials of the three parents by estimating their general combining abilities, as well as minimizing the number of crosses required. If, as found in this study, the general combining ability effect estimates of the parents for grain yield accurately predict performance of later generations, this parent x tester crossing scheme would be an efficient method of assessing the potentials of prospective parents in breeding programs. Close

• 26. [Article] The effect of row spacing, rate and date of planting on yield and yield components of four winter wheat cultivars (Triticum aestivum L. em Thell)

  Four winter wheat cultivars, Bezostaya, Maris-Hobbit, Roussalka and Stephens, selected on the basis of the diversity of their pedigree and phenotype, were planted at Hyslop Experiment Station near Corvallis ...

  Citation × Citation Citation Abstract Copy Title: The effect of row spacing, rate and date of planting on yield and yield components of four winter wheat cultivars (Triticum aestivum L. em Thell) Author: Nadjib, Benacef Four winter wheat cultivars, Bezostaya, Maris-Hobbit, Roussalka and Stephens, selected on the basis of the diversity of their pedigree and phenotype, were planted at Hyslop Experiment Station near Corvallis in Western Oregon to study their performance at three different row spacings (10, 16 and 24 cm), three seeding rates (100, 160, and 240 Kg/ha) and at two seeding dates (October 13 and November 12). A similar experiment was conducted at the Sherman Experiment Station, Moro in Eastern Oregon, using only two winter wheat cultivars, Stephens and Jackmar. Data were obtained on grain yield, tillers and spikes per square meter, heading and anthesis date, plant height, kernels per spike, 1000 kernel weight, test weight and harvest index. At Hyslop Experiment Station, Stephens, Bezostaya and Roussalka produced maximum grain yield at 10 cm row spacing and 160 Kg/ha seeding rate, and Maris-Hobbit at 24 cm row spacing and 160 Kg/ha seeding rate. At Sherman Experiment Station, 30 cm row spacing and 90 Kg/ha seeding rate constitutes the best combination for Stephens, and 30 cm row spacing and 120 Kg/ha seeding rate for the club wheat Jackmar. The interaction between row spacings x cultivars and seeding rates x cultivars indicated that all the cultivars produced high numbers of tillers and spikes per m² at narrow (10 cm) row spacing and high (240 Kg/ha) seeding rate. There were no significant differences between row spacings for heading and anthesis date. Lower seeding rate resulted in later heading date. The cultivar Roussalka was the earliest and Maris-Hobbit the latest in average heading date, Plant height decreased with increased row spacing and increased with increased seeding rate. The plants of the four cultivars were shorter at the second date than at the first. More kernels per spike were produced at the second than at the first date. An increase in seeding rates was accompanied by a decrease in the number of kernels per spike. There were no significant differences between the three row spacings, the three seeding rates and the four cultivars for test weight. The different row spacings and seeding rates did not affect the TOGO kernel weight. Considering the cultivars, Stephens produced a higher 1000 kernel weight at the two seeding dates than Maris- Hobbit, Bezostaya and Roussalka. Title: The effect of row spacing, rate and date of planting on yield and yield components of four winter wheat cultivars (Triticum aestivum L. em Thell) Author: Nadjib, Benacef Four winter wheat cultivars, Bezostaya, Maris-Hobbit, Roussalka and Stephens, selected on the basis of the diversity of their pedigree and phenotype, were planted at Hyslop Experiment Station near Corvallis in Western Oregon to study their performance at three different row spacings (10, 16 and 24 cm), three seeding rates (100, 160, and 240 Kg/ha) and at two seeding dates (October 13 and November 12). A similar experiment was conducted at the Sherman Experiment Station, Moro in Eastern Oregon, using only two winter wheat cultivars, Stephens and Jackmar. Data were obtained on grain yield, tillers and spikes per square meter, heading and anthesis date, plant height, kernels per spike, 1000 kernel weight, test weight and harvest index. At Hyslop Experiment Station, Stephens, Bezostaya and Roussalka produced maximum grain yield at 10 cm row spacing and 160 Kg/ha seeding rate, and Maris-Hobbit at 24 cm row spacing and 160 Kg/ha seeding rate. At Sherman Experiment Station, 30 cm row spacing and 90 Kg/ha seeding rate constitutes the best combination for Stephens, and 30 cm row spacing and 120 Kg/ha seeding rate for the club wheat Jackmar. The interaction between row spacings x cultivars and seeding rates x cultivars indicated that all the cultivars produced high numbers of tillers and spikes per m² at narrow (10 cm) row spacing and high (240 Kg/ha) seeding rate. There were no significant differences between row spacings for heading and anthesis date. Lower seeding rate resulted in later heading date. The cultivar Roussalka was the earliest and Maris-Hobbit the latest in average heading date, Plant height decreased with increased row spacing and increased with increased seeding rate. The plants of the four cultivars were shorter at the second date than at the first. More kernels per spike were produced at the second than at the first date. An increase in seeding rates was accompanied by a decrease in the number of kernels per spike. There were no significant differences between the three row spacings, the three seeding rates and the four cultivars for test weight. The different row spacings and seeding rates did not affect the TOGO kernel weight. Considering the cultivars, Stephens produced a higher 1000 kernel weight at the two seeding dates than Maris- Hobbit, Bezostaya and Roussalka. Close

• 27. [Article] Growth rate and phosphorus uptake of wheat (Triticum aestivum VILL., Host) as a function of soil water suction and soil temperature

  The effect of soil temperature and soil water suction on the rate of phosphorus uptake and growth rate of wheat (Triticum aestivum VILL. , Host) was studied. Plants were grown in perlite slabs separated ...

  Citation × Citation Citation Abstract Copy Title: Growth rate and phosphorus uptake of wheat (Triticum aestivum VILL., Host) as a function of soil water suction and soil temperature Author: Fazilat, Mohammad The effect of soil temperature and soil water suction on the rate of phosphorus uptake and growth rate of wheat (Triticum aestivum VILL. , Host) was studied. Plants were grown in perlite slabs separated from an osmotic solution by a semi-permeable membrane. Measurements were made at temperatures of 10.0, 18.3, 23.9, 32.2, and 35.0°C, and soil water suctions of 0.35 and 2.5 bars. Five week old wheat seedlings were exposed to these conditions. The dry weight of shoots and roots was determined at two day intervals. Plant material extracted was analyzed for phosphorus concentration. The color intensity was measured on a Bausch and Lomb spectronic 20 spectrophotometer of 420 millimicrons. In general, a constant growth rate, which was approached exponentially during the experimental period was found in all treatment combinations. Growth rate for both shoots and roots was slow at low root temperatures and had a maximum rate at a root temperature of 24.0°C. High soil water suction was a limiting factor in growth rate. Phosphorus concentration of shoots and roots was found to approach a constant value during the experimental period according to the equation y = a+be[superscript]-0.07t[superscript]3/2 where y is the phosphorus concentration, t is the time in days, and a and b are constants. Over the entire range of soil temperatures considered the phosphorus concentration of the shoots increased linearlly with the root temperature, but the phosphorus concentration of the roots slightly decreased by increasing soil temperature and did not increase until the root temperature was about 32.0°C. There was no evidence of much variation in percent of total phosphorus uptake transported to the shoot in the experiments. Trans location of phosphorus from roots to shoots did not appear to be a limiting factor for phosphorus uptake at the low root temperature. It was suggested that the low rates of phosphorus uptake at the low root temperatures resulted from the low level of metabolic activity. Title: Growth rate and phosphorus uptake of wheat (Triticum aestivum VILL., Host) as a function of soil water suction and soil temperature Author: Fazilat, Mohammad The effect of soil temperature and soil water suction on the rate of phosphorus uptake and growth rate of wheat (Triticum aestivum VILL. , Host) was studied. Plants were grown in perlite slabs separated from an osmotic solution by a semi-permeable membrane. Measurements were made at temperatures of 10.0, 18.3, 23.9, 32.2, and 35.0°C, and soil water suctions of 0.35 and 2.5 bars. Five week old wheat seedlings were exposed to these conditions. The dry weight of shoots and roots was determined at two day intervals. Plant material extracted was analyzed for phosphorus concentration. The color intensity was measured on a Bausch and Lomb spectronic 20 spectrophotometer of 420 millimicrons. In general, a constant growth rate, which was approached exponentially during the experimental period was found in all treatment combinations. Growth rate for both shoots and roots was slow at low root temperatures and had a maximum rate at a root temperature of 24.0°C. High soil water suction was a limiting factor in growth rate. Phosphorus concentration of shoots and roots was found to approach a constant value during the experimental period according to the equation y = a+be[superscript]-0.07t[superscript]3/2 where y is the phosphorus concentration, t is the time in days, and a and b are constants. Over the entire range of soil temperatures considered the phosphorus concentration of the shoots increased linearlly with the root temperature, but the phosphorus concentration of the roots slightly decreased by increasing soil temperature and did not increase until the root temperature was about 32.0°C. There was no evidence of much variation in percent of total phosphorus uptake transported to the shoot in the experiments. Trans location of phosphorus from roots to shoots did not appear to be a limiting factor for phosphorus uptake at the low root temperature. It was suggested that the low rates of phosphorus uptake at the low root temperatures resulted from the low level of metabolic activity. Close

• 28. [Article] Effect of moisture stress on yield and quality of winter wheat seed

  Two experiments were conducted to determine the effects of moisture stress on physiological changes that occur during the vegetative and reproductive stages of the wheat (Triticum aestivum L.) plant, and ...

  Citation × Citation Citation Abstract Copy Title: Effect of moisture stress on yield and quality of winter wheat seed Author: Assuncao, Marcos Vinicius Two experiments were conducted to determine the effects of moisture stress on physiological changes that occur during the vegetative and reproductive stages of the wheat (Triticum aestivum L.) plant, and to relate these effects to seed yield, quality and performance. In a field experiment, different levels of moisture stress were obtained by establishing plots in two rainfall areas, and by planting on three different dates in the dryland area. Seed development and maturation occurred under extreme moisture stress in Moro (254mm annual rainfall), while stress at Corvallis (1020 mm annual rainfall) was low. Plants from the early fall planting were subjected to the most stress because of the greater fall growth which removed much of the soil moisture. Lowest seed yields occurred under the greatest moisture stress conditions, primarily because of a reduced number of seeds per spike. Seed size was the quality component most affected by moisture stress. Smaller seed size was associated with lower soil water potential, higher leaf area index during vegetative growth, and higher specific leaf weight and water soluble carbohydrate content of the plants after anthesis. Water soluble carbohydrate content was particularly high in the rachises of the most severely stressed plants, indicating a reduced rate of translocation to the developing seeds. Embryo weight was also reduced in the more stressed plants in proportioa to the reduction in seed weight. The protein contents of seeds from all three moisture stress levels at Moro were similar. Seeds developed under the most severe water stress had the highest respiratory quotient and lowest glutamic acid decarboxylase activity. The growth rate of seedlings produced by these seeds was 29% lower than that from seeds from the less stressed plots. A greenhouse experiment was conducted to study the effects of water stress under controlled conditions. Plants were grown under three moisture regimes (600, 300 and 150 ml water/pot/day) from the time awns were first visible on the main stem until maturity. Water-stressed plants had smaller leaf area and leaf dry weight, higher specific leaf weight, earlier leaf senescence, lower dry weight, and lower seed yield. On the other hand, water-stressed plants produced larger seeds, with heavier embryos, higher protein content, lower CO₂ evolution and lower respiratory quotient. These seeds in turn produced seedlings with greater vigor in terms of seedling growth rate. Because of the compensation ability of the wheat plant, development of management practices to decrease certain yield components in favor of enhanced seed quality is worthy of further study. Title: Effect of moisture stress on yield and quality of winter wheat seed Author: Assuncao, Marcos Vinicius Two experiments were conducted to determine the effects of moisture stress on physiological changes that occur during the vegetative and reproductive stages of the wheat (Triticum aestivum L.) plant, and to relate these effects to seed yield, quality and performance. In a field experiment, different levels of moisture stress were obtained by establishing plots in two rainfall areas, and by planting on three different dates in the dryland area. Seed development and maturation occurred under extreme moisture stress in Moro (254mm annual rainfall), while stress at Corvallis (1020 mm annual rainfall) was low. Plants from the early fall planting were subjected to the most stress because of the greater fall growth which removed much of the soil moisture. Lowest seed yields occurred under the greatest moisture stress conditions, primarily because of a reduced number of seeds per spike. Seed size was the quality component most affected by moisture stress. Smaller seed size was associated with lower soil water potential, higher leaf area index during vegetative growth, and higher specific leaf weight and water soluble carbohydrate content of the plants after anthesis. Water soluble carbohydrate content was particularly high in the rachises of the most severely stressed plants, indicating a reduced rate of translocation to the developing seeds. Embryo weight was also reduced in the more stressed plants in proportioa to the reduction in seed weight. The protein contents of seeds from all three moisture stress levels at Moro were similar. Seeds developed under the most severe water stress had the highest respiratory quotient and lowest glutamic acid decarboxylase activity. The growth rate of seedlings produced by these seeds was 29% lower than that from seeds from the less stressed plots. A greenhouse experiment was conducted to study the effects of water stress under controlled conditions. Plants were grown under three moisture regimes (600, 300 and 150 ml water/pot/day) from the time awns were first visible on the main stem until maturity. Water-stressed plants had smaller leaf area and leaf dry weight, higher specific leaf weight, earlier leaf senescence, lower dry weight, and lower seed yield. On the other hand, water-stressed plants produced larger seeds, with heavier embryos, higher protein content, lower CO₂ evolution and lower respiratory quotient. These seeds in turn produced seedlings with greater vigor in terms of seedling growth rate. Because of the compensation ability of the wheat plant, development of management practices to decrease certain yield components in favor of enhanced seed quality is worthy of further study. Close

• 29. [Article] Effects of three herbicides on yields of five cultivars of winter wheat (Triticum aestivum L. em Thell)

  With the development of new selective herbicides and the frequent change in commercial wheat cultivars, information is needed as to the possible interaction between cultivars and herbicides. The responses of ...

  Citation × Citation Citation Abstract Copy Title: Effects of three herbicides on yields of five cultivars of winter wheat (Triticum aestivum L. em Thell) Author: Yahyaoui, Amor With the development of new selective herbicides and the frequent change in commercial wheat cultivars, information is needed as to the possible interaction between cultivars and herbicides. The responses of five genotypically diverse wheat cultivars (Bezostaya, Daws, Maris Hobbit, Stephens and Yamhill) to diuron [3-(3,4-dichloropheny1)-1,1- dimethylurea], diclofop methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate and 2,4-D (2,4-dichlorophenoxy acetic acid) herbicides were compared under field and greenhouse conditions during the 1979-80 growing season. Grain yield was considered as a measure of herbicide injury when compared to the control plots for each cultivar. Effect on components of yield, plant height and grain protein content also were investigated. Differences in yield performance and related agronomic characters could be attributed to specific herbicides, designated rates and growth stages at the time of application. The lower (1.4 kg/ha) rate of diuron, diclofop and 2,4-D reduced yields less than the higher rate (2.8 kg/ha). Diuron and diclofop applied at the earlier (three to to five leaf) growth stage caused greater yield reductions than when applied at the later (five to six tiller) growth stage. Differential yield responses were found among and within the five winter wheat cultivars. The higher rate of diuron (2.8 kg/ha) caused the most injury in all of the cultivars tested. Major injury from diclofop occurred on the cultivar Maris Hobbit with minor effects on the other four cultivars. The primary reduction in yield from application of 2,4-D was to the cultivar Bezostaya. Among the five wheat cultivars tested in this experiment, Daws was the most tolerant to the three herbicides tested. Among the yield components (number of spikes per unit area, kernels per spike and 1000 kernel weight), number of kernels per spike accounted for most of the variation in yield. The data showed a direct relationship between kernel number and grain yield. Grain protein percentage of Daws, Maris Hobbit, Stephens and Yamhill significantly increased at the higher rate of diuron; whereas a similar increase was noted only in Bezostaya at the lower rate of 2,4-D. These increases in protein were associated with significant decreases in yield. Yield reductions due to herbicide treatments were generally lower than those due to weed competition. Reductions in yield and corresponding changes in the other agronomic characteristics observed in this experiment were the result of concentrations which are higher than those normally used in spraying wheat for weed control. This high chemical dosage was chosen for each herbicide to assure a greater differential response among and within the wheat cultivars. It also provided information for the plant breeder as to which cultivars had higher levels of tolerance. Such information is important when making hybrid combinations for the development of future varieties if higher levels of tolerance to specific herbicides are required. Title: Effects of three herbicides on yields of five cultivars of winter wheat (Triticum aestivum L. em Thell) Author: Yahyaoui, Amor With the development of new selective herbicides and the frequent change in commercial wheat cultivars, information is needed as to the possible interaction between cultivars and herbicides. The responses of five genotypically diverse wheat cultivars (Bezostaya, Daws, Maris Hobbit, Stephens and Yamhill) to diuron [3-(3,4-dichloropheny1)-1,1- dimethylurea], diclofop methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate and 2,4-D (2,4-dichlorophenoxy acetic acid) herbicides were compared under field and greenhouse conditions during the 1979-80 growing season. Grain yield was considered as a measure of herbicide injury when compared to the control plots for each cultivar. Effect on components of yield, plant height and grain protein content also were investigated. Differences in yield performance and related agronomic characters could be attributed to specific herbicides, designated rates and growth stages at the time of application. The lower (1.4 kg/ha) rate of diuron, diclofop and 2,4-D reduced yields less than the higher rate (2.8 kg/ha). Diuron and diclofop applied at the earlier (three to to five leaf) growth stage caused greater yield reductions than when applied at the later (five to six tiller) growth stage. Differential yield responses were found among and within the five winter wheat cultivars. The higher rate of diuron (2.8 kg/ha) caused the most injury in all of the cultivars tested. Major injury from diclofop occurred on the cultivar Maris Hobbit with minor effects on the other four cultivars. The primary reduction in yield from application of 2,4-D was to the cultivar Bezostaya. Among the five wheat cultivars tested in this experiment, Daws was the most tolerant to the three herbicides tested. Among the yield components (number of spikes per unit area, kernels per spike and 1000 kernel weight), number of kernels per spike accounted for most of the variation in yield. The data showed a direct relationship between kernel number and grain yield. Grain protein percentage of Daws, Maris Hobbit, Stephens and Yamhill significantly increased at the higher rate of diuron; whereas a similar increase was noted only in Bezostaya at the lower rate of 2,4-D. These increases in protein were associated with significant decreases in yield. Yield reductions due to herbicide treatments were generally lower than those due to weed competition. Reductions in yield and corresponding changes in the other agronomic characteristics observed in this experiment were the result of concentrations which are higher than those normally used in spraying wheat for weed control. This high chemical dosage was chosen for each herbicide to assure a greater differential response among and within the wheat cultivars. It also provided information for the plant breeder as to which cultivars had higher levels of tolerance. Such information is important when making hybrid combinations for the development of future varieties if higher levels of tolerance to specific herbicides are required. Close

• 30. [Article] Selective control of volunteer wheat (Triticum aestivum (L.) em. Thell.) in new seedlings of alfalfa (Medicago sativa L.) with fluazifop-butyl and sethoxydim

  Volunteer winter wheat (Triticum aestivum 'Daws') severely suppressed growth of fall-planted alfalfa (Medicago sativa (L.) 'Vernal') seedlings. Wheat competition began soon after alfalfa emerged and continued until ...

  Citation × Citation Citation Abstract Copy Title: Selective control of volunteer wheat (Triticum aestivum (L.) em. Thell.) in new seedlings of alfalfa (Medicago sativa L.) with fluazifop-butyl and sethoxydim Author: Ott, Pablo Volunteer winter wheat (Triticum aestivum 'Daws') severely suppressed growth of fall-planted alfalfa (Medicago sativa (L.) 'Vernal') seedlings. Wheat competition began soon after alfalfa emerged and continued until the first forage harvest the following May. Alfalfa yield at the first cutting was reduced by 1% for each day volunteer wheat was allowed to grow within the period of 20 to 41 days after planting. When the wheat remained until harvest, alfalfa yield was reduced by 85%. Fluazifop-butyl (+) -butyl 2-[4-[[5-(trifluoromethyl)- 2- pyridinyl] oxy] phenoxy] propanoate and sethoxydim 2- (1- (ethoxyimino)butyl] 5- [2- (ethylthio)propyl] -3-hydroxy- 2-cyclohexen-l-one at rates as high as 3.2 kg/ha (plus phytobland oil at 2.3 L/ha) did not injure the alfalfa or reduce the yield of alfalfa hay when applied at any stage of growth from the unifoliate to the fully developed stages. Control of wheat was better when fluazifop-butyl and sethoxydim were applied in the fall than in the summer. Both herbicides controlled wheat slightly better when applied in the one- to five- tiller stages than at earlier or later stages of growth. In general, fluazifop-butyl was more effective than sethoxydim when applied at any given rate. Under favorable conditions, rates of fluazifop-butyl and sethoxydim as low as 0.12 and 0.18 kg/ha, respectively, killed wheat. Wheat growth was suppressed at even lower rates. However, higher rates (0.2 and 0.4 kg/ha of fluazifop- butyl and sethoxydim, respectively) were required to provide a long term effect under a broad range of conditions. The activity of fluazifop-butyl applied at the twotiller stage of wheat took place mainly through foliar rather than root exposure. Fluazifop-butyl at 0.2 kg/ha killed wheat regardless of the soil moisture content (8% vs 15%). The activity of fluazifop-butyl at 0.12, 0.18, and 0.24 kg/ha on wheat was severely reduced when combined with the dimethylamine salt of 2,4-DB [4- (2,4- dichlorophenoxy) butyric acid] at 1.8 kg/ha, but the antagonism was overcome by increasing the rate of the grass killer to 0.36 kg/ha. Title: Selective control of volunteer wheat (Triticum aestivum (L.) em. Thell.) in new seedlings of alfalfa (Medicago sativa L.) with fluazifop-butyl and sethoxydim Author: Ott, Pablo Volunteer winter wheat (Triticum aestivum 'Daws') severely suppressed growth of fall-planted alfalfa (Medicago sativa (L.) 'Vernal') seedlings. Wheat competition began soon after alfalfa emerged and continued until the first forage harvest the following May. Alfalfa yield at the first cutting was reduced by 1% for each day volunteer wheat was allowed to grow within the period of 20 to 41 days after planting. When the wheat remained until harvest, alfalfa yield was reduced by 85%. Fluazifop-butyl (+) -butyl 2-[4-[[5-(trifluoromethyl)- 2- pyridinyl] oxy] phenoxy] propanoate and sethoxydim 2- (1- (ethoxyimino)butyl] 5- [2- (ethylthio)propyl] -3-hydroxy- 2-cyclohexen-l-one at rates as high as 3.2 kg/ha (plus phytobland oil at 2.3 L/ha) did not injure the alfalfa or reduce the yield of alfalfa hay when applied at any stage of growth from the unifoliate to the fully developed stages. Control of wheat was better when fluazifop-butyl and sethoxydim were applied in the fall than in the summer. Both herbicides controlled wheat slightly better when applied in the one- to five- tiller stages than at earlier or later stages of growth. In general, fluazifop-butyl was more effective than sethoxydim when applied at any given rate. Under favorable conditions, rates of fluazifop-butyl and sethoxydim as low as 0.12 and 0.18 kg/ha, respectively, killed wheat. Wheat growth was suppressed at even lower rates. However, higher rates (0.2 and 0.4 kg/ha of fluazifop- butyl and sethoxydim, respectively) were required to provide a long term effect under a broad range of conditions. The activity of fluazifop-butyl applied at the twotiller stage of wheat took place mainly through foliar rather than root exposure. Fluazifop-butyl at 0.2 kg/ha killed wheat regardless of the soil moisture content (8% vs 15%). The activity of fluazifop-butyl at 0.12, 0.18, and 0.24 kg/ha on wheat was severely reduced when combined with the dimethylamine salt of 2,4-DB [4- (2,4- dichlorophenoxy) butyric acid] at 1.8 kg/ha, but the antagonism was overcome by increasing the rate of the grass killer to 0.36 kg/ha. Close