Physiological characteristics of recent Canada Western Red Spring wheat cultivars: Components of grain nitrogen yield

Transcription

1 Physiological characteristics of recent Canada Western Red Spring wheat cultivars: Components of grain nitrogen yield H. Wang 1,2, T. N. McCaig 1, R. M. DePauw 1, F. R. Clarke 1, and J. M. Clarke 1 1 Research Centre, Agriculture and Agri-Food Canada, Box 1030, Swift Current, Saskatchewan, Canada S9H 3X2. Received 14 November 2002, accepted 21 April Wang, H., McCaig, T. N., DePauw, R. M., Clarke, F. R. and Clarke, J. M Physiological characteristics of recent Canada Western Red Spring wheat cultivars: Components of grain nitrogen yield. Can. J. Plant Sci. 83: Genetic yield gains have been difficult to achieve within the Canada Western Red Spring (CWRS) wheat (Triticum aestivum L.) class, partially because of the requirement for high protein concentration. A previous study indicated that four newer, high-yield CWRS cultivars (registered ) also had higher protein yields. The objective of the present study was to determine if the increase in grain nitrogen (protein) yield of the four newer wheat cultivars, relative to two older cultivars, Neepawa (registered in 1969) and Marquis (introduced in 1909), resulted from increased plant nitrogen uptake, more efficient utilization of nitrogen, or a combination of these factors. The higher nitrogen yields were primarily attributed to more efficient utilization and redistribution of the nitrogen rather than increased uptake of soil nitrogen. The nitrogen harvest index (NHI) of the new cultivars, considered as a group, was higher than the NHI of Neepawa, which in turn was higher than that of the much older cultivar Marquis. The NHI of each of the new cultivars was higher than that of Marquis. The nitrogen concentration in the non-grain tissue at maturity (NGNC M ) of the new cultivars, considered as a group, was lower than that of Neepawa, which in turn was lower than the NGNC M of Marquis. At maturity, all five tissues (leaf blade, stem plus sheath, peduncle, glume, and rachis) for the new cultivars and Neepawa had lower nitrogen concentrations than for the corresponding tissues of Marquis. The nitrogen concentration of the peduncle and leaf-blade tissues of the new cultivars, as a group, were also lower at maturity than the corresponding nitrogen concentrations for Neepawa. The results suggest that low non-grain nitrogen concentration at harvest is associated with improved NHI and grain nitrogen yield in CWRS wheat. This information may improve our understanding of the higher protein yields that have been achieved within this class, and assist in the selection of future parents. Key words: Nitrogen harvest index, nitrogen uptake, nitrogen yield, protein, remobilization, Triticum aestivum Wang, H., McGaig, T. N., DePauw, R. M., Clarke, F. R. et Clarke, J. M Propriétés physiologiques de quelques nouveaux cultivars de blé roux de printemps de l Ouest canadien : composantes du rendement en azote du grain. Can. J. Plant Sci. 83: Il est difficile de réaliser des gains génétiques avec le blé (Triticum aestivum) roux de printemps de l Ouest canadien (BRPO), à cause notamment de la forte concentration en protéines requise. Selon une étude antérieure, quatre nouveaux cultivars de BRPO à rendement élevé (homologués de 1994 à 1997) présentent aussi un fort rendement en protéines. La présente étude devait établir si le rendement en azote du grain (protéines) plus élevé de ces quatre cultivars, comparativement à celui de deux variétés plus anciennes, en l occurrence Neepawa (homologué en 1969) et Marquis (homologué en 1909), venait d une plus grande absorption d azote par la plante, d une meilleure assimilation de cet élément ou d une combinaison de ces facteurs. Le plus fort rendement azoté résulte principalement d une meilleure assimilation et redistribution de l azote et non d une plus grande absorption. L indice de production d azote (IPA) des nouveaux cultivars, pris collectivement, dépasse celui de Neepawa, qui est lui-même plus élevé que celui de Marquis, cultivar beaucoup plus ancien. L IPA des nouveaux cultivars était toujours supérieur à celui de Marquis. À maturité, la concentration d azote dans les autres tissus que le grain des nouveaux cultivars, pris collectivement, était plus faible que celle de Neepawa, plus faible elle aussi que celle de Marquis. À maturité, les cinq tissus (limbe des feuilles, tige et gaine, pédoncule, glume et rachis) des nouveaux cultivars et de Neepawa renfermaient moins d azote que les tissus correspondants chez Marquis. À maturité, la concentration d azote dans le pédoncule et le limbe des feuilles était aussi plus faible chez les nouvelles variétés, prises collectivement, que chez Neepawa. On en conclut qu une faible concentration en azote dans les autres tissus que le grain à la récolte aboutit à un meilleur IPA et à un rendement supérieur du grain en azote chez le BRPO. Ceci pourrait nous aider à mieux comprendre la hausse du rendement en protéines réalisé avec ce type de blé et faciliter la sélection de futures lignées parentales. Mots clés: Indice de production d azote, absorption d azote, rendement azoté, protéine, remobilisation, Triticum aestivum 2 To whom correspondence should be addressed ( wangh@agr.gc.ca). 699 Abbreviations: CWRS, Canada Western Red Spring; GN M, grain nitrogen at physiological maturity; GS, Zadoks- Chang-Konzak growth scale; NGN M, non-grain nitrogen at maturity; NGNC M, non-grain nitrogen concentration at maturity; NHI, nitrogen harvest index; PN A, plant nitrogen at anthesis; PN M, plant nitrogen at maturity; RN, remobilized nitrogen; WBWC, Western Bread Wheat Co-operative Test.

2 700 CANADIAN JOURNAL OF PLANT SCIENCE The CWRS class represents high-protein wheat suitable for the production of high-volume pan breads, certain types of Asian noodles, and for blending to improve lowprotein wheat. Because of these quality requirements, CWRS breeders attempt to simultaneously select for high grain yield and high protein concentration. This is difficult because of the well-documented, negative relationship between grain yield and protein concentration (McNeal et al. 1972; Jenner et al. 1991; Costa and Kronstad 1994; Simmonds 1995). Fortunately, the negative correlations between grain yield and protein concentration, although significant, are often low (Cox et al. 1985), indicating that it should be possible to increase grain yield without decreasing protein concentration. Within a specific environment, the genetic component of grain protein (nitrogen) yield is represented by the product of grain yield and grain protein (nitrogen) concentration. However, within the CWRS class, the economic requirement of producers for high grain yield has limited genetic increases in protein concentration through the negative relationship mentioned above. Genetic decreases in protein concentration have been prevented by the quality requirements and the registration process in Canada. Consequently, the genetic component of grain protein concentration has essentially been held constant within the CWRS class since Marquis was introduced almost 100 yr ago (Wang et al. 2002). This hypothesis is supported by long-term data from the Canadian Grain Commission (2001); when the annual mean protein concentration of CWRS wheat (all milling grades) harvested across the prairies for the 75-yr period was plotted against year, the mean protein concentration was 13.6% (13.5% moisture basis) and the slope of the regression line was zero, indicating that the protein concentration of CWRS wheat has remained static over time, except for yearly variation due to weather. Therefore, within the CWRS class, genetic differences in grain protein yield are closely associated with genetic differences in grain yield. At the physiological level, grain protein yield is influenced by factors such as plant nitrogen uptake, nitrogen distribution within the plant, and the amount of nitrogen that is remobilized to the grain. Genetic differences in nitrogen uptake in hard red spring wheat have been reported by Beninati and Busch (1992). Grain protein yield was correlated with total plant nitrogen at maturity and NHI in both hard red spring (Löffler et al. 1985; McKendry et al. 1995) and durum (Desai and Bhatia 1978) wheat. Genetic differences in nitrogen remobilization have been reported in soft red winter wheat (Van Sanford and MacKown 1987). Clarke et al. (1990) reported genetic differences in nitrogen remobilization among cultivars representing different Canadian wheat classes. Marquis was the first bread-wheat cultivar widely grown in western Canada (Morrison 1960). Neepawa was registered in 1969 (Campbell 1970) and yielded 17% more than Marquis in the WBWC tests over 22 yr (McCaig and DePauw 1995). In an earlier report, Wang et al. (2002) examined the yield components of four newer CWRS cultivars, registered in the past 10 yr, which combined high grain yield and protein concentration, relative to the earlier cultivars Marquis and Neepawa. The higher grain yields, at equal or slightly higher protein concentrations, also meant that the newer cultivars had larger grain protein yields than the older cultivars. However, the WBWC tests provided no information as to whether the increased grain protein yield resulted from increased plant nitrogen uptake, more efficient utilization of nitrogen, or a combination of these factors. If the increased protein yield was due to increased nitrogen uptake, then there could be implications regarding the fertilizer requirements of the newer cultivars to permit full expression of these traits. Improved understanding of the nitrogen uptake and remobilization might allow us to develop more efficient selection criteria for high yield and protein cultivars for western Canada. The objective of the present study was to determine if the increase in grain nitrogen (protein) yield of four newer wheat cultivars, relative to two older cultivars, resulted from increased plant nitrogen uptake, more efficient utilization of nitrogen, or a combination of these factors. MATERIALS AND METHODS Some details of this experiment related to genotype selection, growth conditions, and measurement of yield components have been reported earlier (Wang et al. 2002). Briefly, two old and four new high-quality CWRS cultivars were used in this study. Old cultivars were Marquis (Morrison 1960) and Neepawa (Campbell 1970). New cultivars were AC Barrie (McCaig et al. 1996), AC Cadillac (DePauw et al. 1998), AC Elsa (Clarke et al. 1997), and AC Intrepid (DePauw et al. 1999), which were developed at the Semiarid Prairie Agricultural Research Centre (SPARC), Swift Current, evaluated in the WBWC test over the period , and registered over the period The tests were conducted on a Swinton loam soil (Orthic Brown Chernozem) near Swift Current, SK, (50 17 N, W) from 1998 to 2000, in a randomized complete block design with four replications. Trials were grown on land that was fallow in the previous year. Each plot was 16 rows, 3 m long, 0.23 m between rows, with four rows of spring-seeded winter wheat between plots (no winter wheat between plots in 1999). Monoammonium phosphate and ammonium sulphate were broadcast each year before seeding with targets of 112 kg ha 1 available N and 67 kg ha 1 available P based on soil tests at the end of October in each year prior to spring seeding. The seeding rate was 250 viable kernels m 2 adjusted according to germination tests carried out prior to seeding. Seeding dates were 28 April 1998, 26 May 1999, and 9 May The only irrigation was 48 mm applied on 16 July 1998, when conditions were very dry. Daily maximum and minimum air temperature and precipitation were recorded for the growing season [1 May to 31 July (Campbell et al. 1988)] at a weather site located 100 to 200 m from the test site (Wang et al. 2002). Phenological development was recorded for each plot every 2 3 d using the Zadoks-Chang-Konzak growth scale (GS) ( Zadoks et al. 1974). Based upon the average GS for the six cultivars, all plants in a random 50-cm row from each plot were sampled, on the same day, for above ground biomass at

3 WANG ET AL. COMPONENTS OF GRAIN NITROGEN YIELD OF SPRING WHEAT CULTIVARS 701 Fig. 1. (a) Total aboveground plant dry matter, (b) non-grain dry matter, (c) nitrogen, and (d) non-grain nitrogen at four growth stages (GS 15, five-leaf; GS 39, flag-leaf ligule visible; GS 69, anthesis complete; GS 89, physiological maturity; Zadoks et al. 1974) for the means (± 1 SE) of six cultivars grown at Swift Current, SK for 3 yr. the following growth stages: GS15 (five main-stem leaves), GS39 (flag-leaf ligule visible), GS69 (anthesis complete; hereafter referred to as anthesis growth stage), and GS89 (physiological maturity). Because results from WBWC tests (McCaig and DePauw 1995; McCaig et al. 1996; Clarke et al. 1997; DePauw et al. 1998, 1999) indicated that the period from seeding to maturity was similar for each of the six cultivars, differing by a maximum of approximately 3 d, all cultivars were sampled on the same day. Plants were separated into leaf blades, stem plus sheath (hereafter referred to as stem ), peduncle, glume, rachis, and kernel, depending upon the growth stage. No attempt was made to retrieve dead leaf tissue that may have fallen to the ground prior to sampling. Samples were oven dried at 60 C for a minimum of 72 h and weighed. The vegetative components were ground on a Wiley mill (Thomas Scientific, Swedesboro, NJ) fitted with a 2-mm screen. Grain samples were ground on a Udy Cyclone Sample Mill (Udy Corp., Fort Collins, CO) fitted with a 1-mm screen. Nitrogen was determined by the Kjeldahl method (Williams 1984). Grain protein concentration (13.5% moisture basis) was determined by near-infrared spectroscopy calibrated with samples from the Grain Research Laboratory (Winnipeg, MB). NHI refers to the proportion of total aboveground nitrogen located in the grain at physiological maturity. Remobilized nitrogen (RN) for a tissue was calculated as the amount of nitrogen present in the tissue at the end of anthesis minus the nitrogen present at physiological maturity. Statistical Analysis All dependent variables were analyzed with the PROC MIXED procedure of SAS software (SAS Institute, Inc. 1996) with the REML option for each year with cultivars fixed and replications random. Bartlett s test for homogeneity of error variances (Steel et al. 1997) was performed over years on each variable. A 3-yr combined analysis was conducted with cultivars fixed and replications, years and cultivar year random. If the error variances were heterogeneous, a REPEATED statement was used to specify a GROUP effect of years. Likelihood ratio χ 2 test was used to determine the significance of year differences. If the cultivar year interaction was significant (P < 0.05), a test for crossover interaction (Azzalini and Cox 1984), as described by Baker (1988), was conducted with α = for calculating the critical t-value (Cornelius et al. 1992). A significant cultivar year crossover interaction indicated that the cultivar ranking was not consistent over years. Means comparisons among cultivars were done by Fisher s protected least significant differences (LSD) based on Student s t distribution. Single degree-of-freedom contrasts were used to compare variable differences between the new group of four cultivars and Neepawa or Marquis using the ESTIMATE statement in the PROC MIXED procedure. An error term of cultivar year was used to calculate the 3-yr combined cultivar LSD. RESULTS AND DISCUSSION Total aboveground plant dry matter, averaged over the six CWRS cultivars, increased throughout the growing season in all years (Fig. 1a). Aboveground, non-grain dry matter increased to a maximum at anthesis and then decreased an average of 10.4% between anthesis and physiological maturity (Fig. 1b). Presumably, the decrease in non-grain dry matter resulted from remobilization of nutrients to the grain, although we can not preclude the possibility that some dead leaf tissue was lost. The dry matter trends for the individual

4 702 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Three-year means for grain nitrogen at maturity (GN M ), plant nitrogen at anthesis (PN A ) and maturity (PN M ), nitrogen harvest index (NHI), non-grain nitrogen at maturity (NGN M ), non-grain nitrogen concentration at maturity (NGNC M ), and remobilized nitrogen (RN) for four new and two old CWRS wheat cultivars grown at Swift Current, SK GN M PN A PN M NHI NGN M NGNC M RN (g m 2 ) (g m 2 ) (g m 2 ) (%) (g m 2 ) (%) (g m 2 ) New cultivars AC Barrie AC Cadillac AC Elsa AC Intrepid Old cultivars Neepawa Marquis LSD (0.05) Cultivar *** NS(0.34) NS(0.08) *** ** *** NS(0.28) Year NS(0.24) NS(0.45) NS(0.29) * NS(0.10) * NS(0.54) Cultivar Year NS(0.94) NS(0.09) NS(0.73) NS(0.33) NS(0.14) * z NS(0.21) *, **, ***, NS, Significant at 0.05, 0.01, 0.001, and non-significant at 0.05 (probability level indicated in parentheses) probability levels, respectively. z Cultivar year crossover interaction was not significant. Fig. 2. Three-year mean comparisons for nitrogen uptake and distribution for Marquis, Neepawa, and four new CWRS cultivars considered as a group (New). Probability values for the single df contrasts between the new group and either Marquis or Neepawa are indicated above the bars for Marquis or Neepawa, respectively. (* P < 0.05, ** P < 0.01, NS non-significant). cultivars were similar to the mean trends shown in Fig. 1a,b, with no consistent differences between old and new cultivars (data not shown). Plant nitrogen reached a maximum at anthesis in 1999 and 2000, but increased between anthesis and physiological maturity in 1998 (Fig. 1c). When wheat is grown under conditions of limited soil moisture during grain filling, most of the plant nitrogen is taken up by anthesis (McNeal et al. 1968; Palta and Fillery 1995; Fangmeier et al. 1999). However, nitrogen may be taken up by roots deeper in the soil after anthesis if there is sufficient moisture (Meinke et al. 1997). McMullan et al. (1988) also presented evidence that uptake of nitrogen after anthesis was contingent upon sufficient soil moisture. The late uptake of nitrogen in 1998 probably resulted from the 48-mm irrigation that was applied during grain filling that year. No irrigations were applied in 1999 or 2000, and single-day precipitation events during grain filling in 1999 or 2000 never exceeded 17 mm. An analysis of the long-term weather data for Swift Current indicated that single-day precipitations as large as 48 mm, during our normal grain-filling period, have only happened in 3 of the past 100 yr (data not shown). Two earlier field trials at Swift Current, SK demonstrated that there was little net, post-anthesis nitrogen uptake without supplemental irrigation to augment soil moisture during grain filling

5 WANG ET AL. COMPONENTS OF GRAIN NITROGEN YIELD OF SPRING WHEAT CULTIVARS 703 Fig. 3. Three-year mean comparisons for (a) nitrogen harvest index, and (b) non-grain nitrogen concentration at maturity for Marquis, Neepawa, and four new CWRS cultivars considered as a group (New). Probability values for the single df contrasts between the new group and either Marquis or Neepawa are indicated above the bars for Marquis or Neepawa, respectively. (* P < 0.05, ** P < 0.01). (Campbell et al. 1977; Clarke et al. 1990). These results suggest that nitrogen uptake in this semi-arid region is normally complete by anthesis. Non-grain nitrogen also reached a maximum by anthesis (Fig. 1d). However, the non-grain nitrogen decreased an average of 70.6% between anthesis and physiological maturity. Because the relative decrease in non-grain nitrogen was much greater than the relative decrease in non-grain dry matter (Fig. 1b), most of the nitrogen represented by the decrease was probably remobilized to the developing grain, although a small proportion was probably lost through ammonia volatilization (Parton et al. 1988). The nitrogen trends for the individual cultivars were also very similar to the mean trends shown in Fig. 1c,d, with no consistent differences between old and new cultivars (data not shown). We previously reported that grain yields of the four new cultivars averaged 7.9% higher than Neepawa when grown in the multi-location WBWC test for 3 yr, and 5.9 and 34.3% higher than Neepawa (P = 0.10) and Marquis, respectively, when grown at Swift Current for the three years in the present test (Wang et al. 2002). Individually, each of the new cultivars produced significantly more grain nitrogen at maturity (GN M ), per unit area, than Marquis (Table 1), and as a group, more GN M than Marquis or Neepawa (Fig. 2). The GN M values, based on Kjeldahl analysis of growth samples at physiological maturity, were corroborated by NIR protein analyses of combine-harvest samples; the new cultivars, as a group, produced 33 and 6% more protein, per unit area, than Marquis or Neepawa (P = 0.07), respectively (average of 3 yr; data not shown). Averaged over years, there were no significant cultivar differences in total plant nitrogen at either anthesis (PN A ) or maturity (PN M ) (Table 1). PN M for the new cultivars as a group was significantly higher than that of Marquis, but not different than that of Neepawa (Fig. 2). The results do not indicate that the new cultivars take up more nitrogen than older ones after anthesis; rather, it is possible that the older cultivars lose nitrogen between anthesis and maturity, but this would require further testing to confirm. The results suggest that the new cultivars produced higher protein yields primarily by utilizing plant nitrogen more efficiently rather than extracting more nitrogen from the soil. NHI, which indicates how efficiently the plant partitions nitrogen between grain and non-grain tissues at maturity, has been suggested as a selection tool for genotypes or parents with high grain yield and protein concentration (Löffler and Busch 1982; Clarke et. al. 1990). The NHI of the new cultivars, as a group, was 5 and 28% higher than that of Neepawa and Marquis, respectively (Fig. 3a). The increased NHI of the new cultivars is another indication that they are utilizing nitrogen more efficiently than the older cultivars, and accounts for most of the increased grain nitrogen yields relative to the old cultivars. The NHI of Marquis was especially low, partially because of high amounts of nitrogen remaining in the non-grain tissue of Marquis at maturity (NGN M, Table 1). The NGN M is calculated as the product of non-grain dry matter and NGNC M. Non-grain dry matter at maturity, as reported previously (Wang et al. 2002), did not differ among Neepawa, Marquis, and the new cultivars as a group. However, the NGNC M of the new cultivars, as a group, was 30% lower than that of Marquis and 11% lower than that of Neepawa (Fig. 3b). Therefore, the decreased NGN M of the new cultivars was primarily attributed to the decreased NGNC M of the new cultivars (Table 1). The decreased NGNC M probably also contributed to the increased NHI of the new cultivars, although NHI is also associated with total harvest index, which was previously reported to be higher for the new cultivars (Wang et al. 2000). Although the cultivar year interaction for NGNC M was significant, the crossover interaction was not, indicating that the cultivar ranking was similar over years. The lower NGNC M suggests that the new cultivars are more efficient at translocating nitrogen from vegetative tissue to grain. The results of McMullan et al. (1988) also suggest

6 704 CANADIAN JOURNAL OF PLANT SCIENCE Table 2. Three-year means for nitrogen concentration at maturity (NC M ), nitrogen per unit area at maturity (N M ), and remobilized nitrogen (RN) for plant tissues of four new and two old CWRS wheat cultivars grown at Swift Current, SK Leaf Stem (plus sheath) Peduncle Glume Rachis NC M N M RN NC M N M RN NC M N M RN NC M N M RN NC M N M RN (%) (g m 2 ) (g m 2 ) (%) (g m 2 ) (g m 2 ) (%) (g m 2 ) (g m 2 ) (%) (g m 2 ) (g m 2 ) (%) (g m 2 ) (g m 2 ) New cultivars AC Barrie AC Cadillac AC Elsa AC Intrepid Old cultivars Neepawa Marquis LSD (0.05) Cultivar *** * NS(0.31) ** ** NS(0.72) *** *** * *** * * *** *** ** Year NS(0.32) * * NS(0.19) NS(0.17) NS(0.98) NS(0.25) * NS(0.99) * NS(0.99) NS(0.95) * * NS(0.15) Cultivar Year *** z ** Y * Z * Y NS(0.24) NS(0.50) NS(0.14) NS(0.13) NS(0.18) NS(0.40) NS(0.13) NS(0.56) NS(0.60) NS(0.12) NS(0.31) *, **, ***, NS, Significant at 0.05, 0.01, 0.001, and non-significant at 0.05 (probability level indicated in parentheses) probability levels, respectively. z Cultivar year crossover interaction was not significant. y Cultivar year crossover interaction for NCM of stem (plus sheath) was significant but only involved changes in rank order within the new cultivars; the crossover interaction for N M of leaf was significant because of changes in rank order between Neepawa and new cultivars. that higher translocation efficiency is a contributing factor to higher grain nitrogen yields, although they did not observe significantly lower nitrogen concentrations in non-grain tissues of genotypes with higher grain nitrogen yields. Leaf protease levels have been related to the remobilization of nitrogen to the developing grain in crops such as wheat (Rao and Croy 1972) and corn (Reed et al. 1980). Cregan and Berkum (1984) suggested that the rate of protein synthesis in the developing seed could be an important factor determining nitrogen movement from vegetative tissues to the grain. Peña (1996) indicated that spike and grain size may be associated with genetic differences in the capacity of the grain to assimilate nitrogen from vegetative tissues. The lower NGNC M of the new cultivars may, therefore, be related to the larger sink size (more kernels per spike and higher kernel weight) found in the new cultivars (Wang et al. 2002). However, it is also possible that leaf proteases are contributing to more efficient breakdown of leaf protein for remobilization. Although the above information suggested that the new cultivars were achieving higher grain nitrogen yields by remobilizing more nitrogen from vegetative tissues, there were no significant differences among cultivars in the amount of remobilized nitrogen (RN; Table 1), nor were there any significant differences in RN between old and new cultivars when the new cultivars were considered as a group (Fig. 2). Because the calculation of RN depended upon growth measurements and nitrogen concentration measurements for several tissues at two stages (anthesis and maturity), true differences in RN may have been masked by the large errors involved in the calculation of such variables. To explain the decreased NGNC M of the new cultivars, relative to both Marquis and Neepawa (Fig. 3b), five nongrain tissues (leaf blade, stem, peduncle, glume, rachis) were examined individually. Nitrogen retranslocation has previously been reported from leaf (Gregory et al. 1981), stem (Simpson et al. 1983), peduncle (Van Sanford and MacKown 1987), glume (Jenner et al. 1991), and rachis (Berecz et al. 1997) tissues. The nitrogen concentrations for all tissues of Marquis were higher than for the corresponding tissues of the new cultivars, individually (Table 2), and as a group (Fig. 4). The nitrogen concentrations of Neepawa leaf blades and peduncle tissues were significantly higher than those of the new cultivars as a group (Fig. 4). Considered individually, three of the four new cultivars exhibited lower leaf-blade and peduncle nitrogen concentrations than Neepawa, while the concentrations for AC Barrie were not significantly lower than those of Neepawa (Table 2). In each of the new cultivars, the amount of nitrogen remaining at maturity in the stem, peduncle, and rachis was less than the nitrogen found in the corresponding tissues of Marquis (Table 2). The new cultivars, as a group, had less nitrogen at maturity than Marquis in all non-grain plant parts, except glumes (Fig. 4). However, there were no significant differences at maturity between the amount of nitrogen in the plant tissues of Neepawa and the tissues of the new cultivars, individually, or as a group. Leaf-blade tissue contributed the greatest amount of remobilized nitrogen, followed by stem, peduncle, glume, and rachis, respectively (Fig. 4, Table 2), although the rachis contributed

7 WANG ET AL. COMPONENTS OF GRAIN NITROGEN YIELD OF SPRING WHEAT CULTIVARS 705 Fig. 4. Three-year mean comparisons for (a) nitrogen concentration at maturity, (b) nitrogen per unit area at maturity, and (c) remobilised nitrogen of non-grain plant tissues for Marquis, Neepawa, and four new CWRS cultivars considered as a group (New). Probability values for the single df contrasts between the new group and either Marquis or Neepawa are indicated above the bars for Marquis or Neepawa, respectively. (* P < 0.05, ** P < 0.01, NS, non-significant). very little. This agrees with results presented by Jenner et al. (1991) that leaves and stems are the most important reserves for nitrogen. In the present study, the amount of RN from the peduncle, glume, and rachis of each of the new cultivars was greater than the RN from the corresponding tissues of Marquis (Table 2). However, there were no significant differences in RN between Neepawa and the new cultivars. For the new cultivars as a group, 21% of the total RN was contributed by the peduncle, compared to 20% for Neepawa and 14% for Marquis. Van Sanford and MacKown (1987) reported that the nitrogen contribution from the peduncle ranged from 10 to 26% of the total RN for a group of nine soft red winter wheat varieties. The results of the present study suggest that the peduncle and glume tissues are more important sources of RN for Neepawa and the new cultivars than they are for Marquis. The above results indicated that nitrogen concentrations at maturity, for leaf-blade and peduncle tissues, represented the most consistent difference between the new and old cultivars. Although the cultivar year interaction was highly significant for leaf-blade tissue, there was not a significant crossover interaction (Table 2). Examination of the individual years for leaf-blade nitrogen concentration at maturity indicated that Marquis was higher than all of the new cultivars, considered individually, in each of the 3 yr, while Neepawa was higher than all of the new cultivars, considered individually, in each of the three years, at the P < 0.10 level of significance (data not shown). Individual year data also suggested that leaf tissue separated new and old cultivars more consistently than peduncle tissue (data not shown), even though the cultivar year interaction was not significant for peduncle nitrogen concentration (Table 2). The metabolic differences responsible for NGNC M may be intimately linked with the ability of the newer cultivars to produce higher grain nitrogen yields. Because the measurement of leaf tissue at maturity could be useful as a means to identify genotypes with low NGNC M, the leaves from different positions on the stem were examined separately. The nitrogen concentrations at maturity of the flag, penultimate, and other leaves were all higher for both Marquis and Neepawa, compared to the new cultivars as a group (Fig. 5). When the new cultivars were considered individually, the nitrogen concentration of the flag leafblade was significantly higher for Marquis and Neepawa than for all of the new cultivars, and the cultivar year interaction was not significant (data not shown). The nitrogen concentration of the penultimate leaf-blade was significantly higher for Neepawa than for three of the new cultivars. The nitrogen concentration of the other leaves was significantly higher for Neepawa than for two of the new cultivars, and nominally higher than the nitrogen concentrations for other two new cultivars. These results suggest that the flag leaf-blade may be the most useful tissue to identify genotypes with low NGNC M. Considerably more nitrogen was also remobilized from the flag leaf-blade than from the penultimate and other leaves (Fig. 5).

8 706 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 5. Three-year mean comparisons for (a) nitrogen concentration at maturity, (b) nitrogen per unit area at maturity, and (c) remobilised nitrogen of leaf tissues for Marquis, Neepawa, and four new CWRS cultivars considered as a group (New). Probability values for the single df contrasts between the new group and either Marquis or Neepawa are indicated above the bars for Marquis or Neepawa, respectively. (* P < 0.05, ** P < 0.01, NS, non-significant). However, our measurements could not detect differences, between old and new cultivars, in the amounts of RN from specific leaf positions (i.e., flag, penultimate, other); as mentioned earlier, this may be associated with the large errors involved in the measurement of RN. ACKNOWLEDGEMENTS We gratefully acknowledge Dale Kern for providing excellent technical assistance, and Agriculture and Agri-Food Canada, including the Matching Investment Initiative, for providing financial support for this research. Azzalini, A. and Cox, D. R Two new tests associated with analysis of variance. J. R. Statist. Soc. B. 46: Baker, R. J Tests for crossover genotype-environmental interaction. Can. J. Plant Sci. 68: Beninati, N. F. and Busch, R. H Grain protein inheritance and nitrogen uptake and redistribution in a spring wheat cross. Crop Sci. 32: Berecz, K., Debreczeni, K. and Presing, M Incorporation of N-15 labelled fertilizer nitrogen into upper vegetative plant parts in wheat and its mobilization during grain development. Plant Physiol. Biochem. 35: Campbell, A. B Neepawa hard red spring wheat. Can. J. Plant Sci. 50: Campbell, C. A., Cameron, D. R., Nicholaichuk, W. and Davidson, H. R Effects of fertilizer N and soil moisture on growth, N content, and moisture use by spring wheat. Can. J. Soil Sci. 57: Campbell, C. A., Zentner, R. P. and Johnson, P. J Effect of crop rotation and fertilization on the quantitative relationship between spring wheat yield and moisture use in southwestern Saskatchewan (Canada). Can. J. Soil Sci. 68: Canadian Grain Commission Quality of 2001 Western Canadian Wheat. Canada Western Red Spring Wheat. [Online] Available: wht01hs04-e.htm [14 November 2002]. Clarke, J. M., Campbell, C. A., Cutforth, H. W., DePauw, R. M. and Winkleman, G. E Nitrogen and phosphorus uptake, translocation, and utilization efficiency of wheat in relation to environment and cultivar yield and protein levels. Can. J. Plant Sci. 70: Clarke, J. M., DePauw, R. M., McCaig, T. N., Fernandez, M. R., Knox, R. E. and McLeod, J. G AC Elsa hard red spring wheat. Can. J. Plant Sci. 77: Cornelius, P. L., Seyedsadr, M. and Crossa, J Using the shifted multiplicative model to search for separability in crop genotype trials. Theor. Appl. Genet. 84: Costa, J. M. and Kronstad, W. E Association of grain protein concentration and selected traits in hard red winter wheat populations in the pacific northwest. Crop Sci. 34: Cox, M. C., Qualset, C. O. and Rains, D. W Genetic variation for nitrogen assimilation and translocation in wheat. II. Nitrogen assimilation in relation to grain yield and protein. Crop Sci. 25:

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