Nitrogen utilization efficiency of safflower hybrids and open-pollinated varieties under Mediterranean conditions

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Field Crops Research 107 (2008) 56–61 www.elsevier.com/locate/fcr

Nitrogen utilization efficiency of safflower hybrids and open-pollinated varieties under Mediterranean conditions Spyridon D. Koutroubas a,*, Despo K. Papakosta b, Alexandros Doitsinis c a

Democritus University of Thrace, School of Agricultural Development, 68200 Orestiada, Greece b Aristotle University of Thessaloniki, School of Agriculture, 54006 Thessaloniki, Greece c Regional Laboratory of Agricultural Extension and Fertilizer Analysis of Central Makedonia, Sindos-Thessaloniki, Greece Received 20 May 2007; received in revised form 19 December 2007; accepted 19 December 2007

Abstract The identification of the factors determining nutrient utilization of safflower (Carthamus tinctorius L.) is useful for the successful introduction of the crop to the cropping system of a region. A field study was conducted to compare and analyze the relative importance of the various component traits causing variation in nitrogen utilization efficiency (NUE) of safflower under Mediterranean conditions. Ten genotypes, four hybrids and six open-pollinated varieties, were grown for two growing seasons without irrigation, on a silty clay (Typic Xerorthent) soil. Seed yield varied greatly among genotypes and ranged from 923 to 3391 kg ha1. Hybrids showed a mean seed yield superiority of 12.5% against varieties. Seed yield was the most important component of seed N yield and its contribution to the total variation in seed N yield among genotypes was at least 53%. NUE for biomass production during the seed-filling period was lower compared to that during the vegetative period. Genotypes differed in NUE for seed production (NUEs) and the differences followed those of nitrogen harvest index (NHI). The contribution of NHI to the total variation in NUEs among genotypes was much greater compared to that of yield per unit seed nitrogen and accounted for more than 79%. NUEs is positively correlated with seed yield, suggesting that high yield was probably associated with more efficient exploitation of nitrogen. NUEs is negatively correlated with (leaf + stem) N concentration at maturity, meaning that low straw N concentration may be indication of higher NUEs. Results indicated that selection for NUE in safflower should be based on multiple criteria rather than just one criterion and also should be accompanied by evaluation for seed yield to ensure an improvement in both traits. # 2007 Elsevier B.V. All rights reserved. Keywords: Carthamus tinctorius; Nitrogen yield; Seed yield; Genotypes

1. Introduction Safflower is a minor, underutilized crop cultivated mainly in dry–hot climates for its seed, which is used for edible oil extraction and as birdseed. Plants have a deep taproot and xerophytic spine attributes that contribute to good drought and heat tolerance (Dajue and Mu¨ndel, 1996). Safflower is thought to have the potential for being an alternative crop to continuous winter cereal monoculture in areas with Mediterranean type of climate (Yau, 2004; Koutroubas and Papakosta, 2005). This possibility seems to be more feasible in Europe after the recent reform of the Common Agricultural Policy (CAP) of the European Union. Under this new situation, farmers are free to produce in response to demand without losing their entitlement

* Corresponding author. Tel.: +30 2552041125; fax: +30 2552041191. E-mail address: [email protected] (S.D. Koutroubas). 0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2007.12.009

to support, as subsidies were decoupled from production. The introduction of safflower in the cropping system of Mediterranean region could increase local production of vegetable oil and protein-rich meals for feeding livestock. It also could improve the overall nitrogen use efficiencies of cropping systems and minimize nitrate leaching to groundwater (Bassil et al., 2002). Seed yield of a safflower crop can be expressed in terms of a set of various components. The direct yield components are number of plants per plot, number of heads per plant, number of seeds per head and weight of seeds (Gilbert and Tucker, 1967). The relative importance of each yield component is affected by many factors, including genotype, environmental conditions and cultural practices. Temperature, and water and nitrogen availability are important parameters affecting yield components in safflower. Low temperatures during winter lengthen the rosette period and thus the vegetative growth stage, an effect that was associated with higher yields from increases in the number of heads and seeds in the head (Abel, 1975). Erie and

S.D. Koutroubas et al. / Field Crops Research 107 (2008) 56–61

French (1969) reported that irrigation increased weight per seed and seeds per head, while decreased the percentage of hollow seed. Safflower response to nitrogen is generally greater than to other nutrients (Weiss, 2000). Nitrogen increases seed yield primarily through its effect on the number of heads per plant and the increase is greater in tertiary and to a lesser extent in secondary heads (Weiss, 2000). When soil nitrogen was maintained at an adequate level, the factor limiting high seed yield was insufficient water supply (Jones and Tucker, 1968). Genotypic variation for nitrogen uptake and nitrogen utilization efficiency has been reported for many small grain crops (May et al., 1991; Kelly et al., 1995; Le Gouis et al., 1999; Koutroubas and Ntanos, 2003), and the possibility of improving nitrogen utilization efficiency through plant breeding has been investigated (Van Ginkel et al., 2001; Ju et al., 2006). Such information is limited for safflower. Koutroubas et al. (2004) reported genotypic and seasonal variation in nitrogen accumulation and translocation. Seasonal differences were mainly related to time of sowing. Autumn sowing was superior to spring sowing in nitrogen accumulation up to anthesis, and this resulted in a greater translocation to seed during the filling period. The identification of the factors affecting nitrogen utilization of safflower is important for the successful introduction of the crop to a given cropping system. Such information could be exploited by growers for adopting the appropriate cultural practices and also by breeders for choosing the most efficient selection criteria in order to improve nitrogen exploitation. The purpose of this study was to compare and analyze the relative importance of the various component traits that cause variation in nitrogen utilization efficiency in a diverse set of safflower genotypes, including new hybrids and open-pollinated varieties, under Mediterranean conditions. 2. Materials and methods The experiments were carried out at the farm of the Aristotle University of Thessaloniki (408540 N, 238000 E), Greece during the 1997–1998 and 1998–1999 growing seasons (referred hereafter as 1998 and 1999, respectively). The soil is a silty clay (Typic Xerorthent) with a pH of 7.85 and 0.85% organic matter. The previous crop was wheat in both growing seasons. Ten safflower genotypes, four hybrids and six open-pollinated cultivars of various origins were used. The hybrids included GW 9003, GW 9005, GW 9022, GW 9023 originated from USA and the cultivars included Montola 2000, Montola 2001, Centennial, C9305 originated from USA, Tucson (AS-55) from Chile and Demetra from Greece. The hybrids GW 9003, GW 9005 and the cultivars Centennial, C9305, and Demetra are of linoleic type and the rest genotypes used are of oleic type. The experiment was arranged in a randomized complete block design with three replications. Plots were 4 m long and consisted of four rows, 0.5 m apart. The experimental area was uniformly fertilized with 100 kg N ha1 in the form of ammonium sulfate and 22 kg P ha1 in the form of superphosphate, both broadcast applied just before planting and incorporated in the soil. Seeds were hand-planted on 19 November 1997 and 16 November

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1998. Due to the frost in winter of 1998, the seedlings were damaged and the experiment was re-sown on 9 March 1999. A rate of 15 seeds per metre of row was used to achieve a final density of approximately 250,000 plants ha1. Plants were grown without supplemental irrigation in both the growing seasons. The crop was kept free of weeds by hand hoeing when necessary. In 1999, trifluralin applied pre-sowing was also used for weed control. Dates of emergence, stem elongation, anthesis and maturity were recorded. Anthesis was scored when florets of the 50% of the heads in a plot had developed and maturity when almost all the heads in a plot showed complete loss of green color. Plant samples, composed of 1-m row segment from each plot, were taken at anthesis and maturity. The plants were cut at ground level and were separated into leaf plus stem, and head at anthesis and also seeds at maturity. All plant samples were dried at 70 8C until constant weight and weighed. The dry vegetative samples were first ground in a hammer mill and then re-ground finely using a 1mm screen. Seed samples were ground using the same screen. The number of heads per plant and the mean number of seeds per head was determined on five consecutive plants from each plot at maturity. Seed weight was taken on 1000 seeds. Seed yield was determined by harvesting the two central rows of each plot using a wheat plot-harvesting machine, after the appropriate screen adjustment. Nitrogen concentration was determined by standard macro-Kjeldahl procedure. In comparing genotypes with respect to nitrogen utilization efficiency the following parameters were calculated: 1. Nitrogen utilization efficiency for biomass accumulation (or physiological efficiency) until anthesis (NUEb-anthesis) = Bwa/Na 2. Nitrogen utilization efficiency for biomass accumulation until maturity (NUEb-maturity) = Bwt/Nt 3. Nitrogen utilization efficiency for seed yield (NUEs) = Sw/Nt 4. Seed yield per unit seed N = Sw/Ns 5. Nitrogen harvest index (NHI) = Ns/Nt, where Bwa: aboveground dry biomass at anthesis, Bwt: aboveground dry biomass at maturity, Sw: seed dry weight, Na: total aboveground N at anthesis, Nt: total aboveground N at maturity and Ns: seed N. Various expressions were constructed and analyzed according to the method suggested by Moll et al. (1982). This analysis involves linearizing the multiplicative relationships by taking logs and then determining the contribution of each component trait to the sum of squares of the resultant trait. The sum of cross products of each component trait by the resultant trait (Sxiyi) divided by the sum of squares of the resultant trait (Syi2) gives the relative contribution of each component variable to resultant variable. This analysis describes the net contribution of each component variable both directly and indirectly through the other variable (Moll et al., 1982). The following expressions were analyzed: 1. Seed N yield = seed yield  seed N concentration, 2. Seed N content per head = seeds per head  seed weight  seed N concentration, and

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3. NUEs = (Sw/Ns)  (Ns/Nt). A statistical analysis was performed according to Steel and Torrie (1980). The homogeneity of variances was checked, and all measured and derived data were subjected to a combined over years analysis of variance (ANOVA). Fisher’s protected least significant difference (LSD) values were calculated and used to compare treatment means. Standard statistical procedures were used for calculating simple correlation coefficients and linear regression equations. 3. Results and discussion The meteorological data recorded during the trial period in each growing season are given in Table 1. Temperature was generally similar in both growing seasons, while total seasonal rainfall was considerable higher in 1998 (286 mm) compared to that in 1999 (154 mm). Genotypes matured almost synchronously at the end of July, irrespective of sowing time. Reproductive period coincided with dry and warm weather conditions in both years. The crop received no rainfall during the reproductive period in 1998 and 28 mm in 1999, distributed in five small events of water (below 10 mm), which means that the benefit from rainfall during seed filling was negligible. Mean daily maximum temperature during the reproductive period was 34 8C in 1998 and 33 8C in 1999. The corresponding values for the mean temperature were 28.2 and 27 8C, respectively. Seed yield was significantly affected by main factors, year (Y) and genotype (G), as well as by their interaction (Table 2). The observed Y  G interaction concerned the ranking of the genotypes in each year, because all genotypes yielded more in 1998 compared to 1999. In 1998, seed yield of the hybrid GW 9003 (3391 kg ha1) was significantly higher than all genotypes except the hybrid GW 9005 (3191 kg ha1) and the variety Tucson (3096 kg ha1). Montola 2001 and Centennial had the lowest seed yield among all genotypes. In 1999, Demetra had higher seed yield (2430 kg ha1) than all genotypes. Centennial, Montola 2001 and GW 9022 had similar seed yield that was lower than all genotypes. Averaged across genotypes, the mean seed yield in 1998 (2638 kg ha1) was by 74% higher compared to that in 1999 (1516 kg ha1). The

increase in seed yield obtained in 1998 ranged from 20% (Demetra) to 127% (GW 9022) and was probably due to the earlier sowing and the higher rainfall compared to 1999. These results are in agreement with those of Yau (2007), who reported that in a semi-arid Mediterranean environment seed yield were higher by 59–169% in fall or early winter sowing than in late winter or early spring sowing. Several other studies conducted in various environments have demonstrated the superiority of fall sowing against spring sowing as for the seed yield (Abel, 1976; Mu¨ndel et al., 1994; Cazzato et al., 1997; Salera, 1997). Heads fertility, as was specified by the number of seeds per head, was an important factor contributed to the seed yield differences between years in our study (data not shown). Averaged across genotypes, in 1998 produced 115% more seeds per head compared to 1999 (28 vs. 13). Head fertility is a genetically controlled trait that is also affected by environmental conditions, such as temperature and water availability (Abel, 1975; Erie and French, 1969; Cazzato et al., 1997). It has been reported that shifting from November to February sowing the number of seeds per head decreased, particularly in tertiary heads (Cazzato et al., 1997). The disadvantage of late sowing safflower in our study was also associated with the low preanthesis dry matter accumulation and translocation to the seeds that, in turn, led to a low seed yield (Koutroubas et al., 2004). Significant differences in seed yield were also detected between genotype groups separated on the basis of genetic constitution (Table 2). Safflower hybrids had, on average, significantly higher seed yield compared to varieties in both years. The over years mean seed yield was 2225 kg ha1 for hybrids and 1978 kg ha1 for varieties, giving a mean seed yield superiority of 12.5% in hybrids. The corresponding yield advantage of hybrids against varieties was 16.1% in 1998 (2878 vs. 2478 kg ha1) and 6.4% in 1999 (1572 vs. 1478 kg ha1), indicating that hybrids showed a better exploitation of early sowing compared to varieties. Corleto et al. (1997) reported that under favourable environmental conditions seed yield of hybrids exceeded that of varieties by 53%. The inconsistency between our study and that of Corleto et al. (1997) regarding the magnitude of the yield superiority of safflower hybrids compared to varieties can be mainly attributed to the differences in genotypes used and climate.

Table 1 Monthly temperature and precipitation at the farm of Aristotle University of Thessaloniki, Greece during the growing season in 1997–1998 and 1998–1999 Month

Average temperature (8C) Minimum

November December January February March April May June July

Maximum

Mean

Total precipitation (mm)

1997–1998

1998–1999

1997–1998

1998–1999

1997–1998

1998–1999

1997–1998

1998–1999

7.1 2.0 1.0 2.2 1.1 8.2 13.1 18.0 20.2

4.1 6.0 7.0 4.1 4.3 7.8 12.4 18.1 21.5

12.9 9.9 8.5 13.4 12.4 21.1 24.1 31.7 34.9

11.8 10.1 13.1 18.0 14.7 20.8 25.5 31.2 33.0

16.2 5.2 6.7 5.2 7.2 15.9 18.8 26.2 28.8

11.1 3.5 4.2 4.4 9.9 14.8 19.7 24.9 28.1

22.0 51.5 46.0 56.0 9.0 5.0 105.0 0.0 0.0

162.0 16.5 19.0 31.0 50.5 33.5 26.0 43.0 48.5

S.D. Koutroubas et al. / Field Crops Research 107 (2008) 56–61

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Table 2 Seed yield, shoot N concentration, seed N yield and N yield components, and NUE of 10 safflower genotypes grown in 1998 and 1999 Seed yield (kg ha1)

Seed N Seed N yield Seed N Shoot N concentration at concentration (kg ha1) content per anthesis (g kg1) (g kg1) head (mg)

1998 GW 9003 GW 9005 GW 9022 GW 9023 Montola 2000 Montola 2001 C 9305 Centennial Tucson Demetra Mean hybrids Mean varieties Overall mean

3391 3191 2609 2320 2330 1819 2735 1982 3096 2905 2878 2957 2638

10.5 9.4 10.6 11.7 11.8 11.8 13.3 12.0 11.2 11.4 10.6 13.7 11.4

53.0 52.8 57.5 57.4 52.5 59.1 56.8 52.8 52.2 59.5 55.2 64.7 55.3

179.6 168.5 150.0 133.1 122.2 107.5 155.4 104.5 161.6 172.8 157.8 163.6 145.5

0.063 0.060 0.073 0.042 0.038 0.047 0.071 0.048 0.074 0.074 0.060 0.069 0.059

56.1 60.7 56.0 55.6 52.4 53.8 50.4 51.7 56.2 49.0 57.1 61.8 54.2

41.8 43.6 39.9 37.7 39.7 36.3 36.9 41.9 40.2 36.3 40.8 45.3 39.4

13.7 13.4 11.3 11.8 11.9 11.6 12.8 12.0 12.8 11.0 12.6 14.1 12.2

18.9 18.9 17.4 17.4 19.1 16.9 17.6 19.0 19.2 16.8 18.2 21.1 18.1

0.725 0.708 0.650 0.674 0.626 0.685 0.727 0.631 0.670 0.656 0.689 0.781 0.675

1999 GW 9003 GW 9005 GW 9022 GW 9023 Montola 2000 Montola 2001 C 9305 Centennial Tucson Demetra Mean hybrids Mean varieties Overall mean

1940 1643 1147 1557 1420 1163 1487 923 1447 2430 1572 1740 1516

7.9 8.3 5.9 11.4 10.4 10.6 10.7 8.2 9.8 6.6 8.4 10.8 9.0

28.1 29.1 28.9 28.6 25.6 28.2 31.2 30.3 29.6 27.5 28.7 33.5 28.7

54.4 47.9 33.1 44.5 36.4 32.8 46.3 28.0 42.8 66.9 45.0 49.7 43.3

0.016 0.017 0.012 0.016 0.014 0.011 0.019 0.009 0.014 0.020 0.015 0.017 0.015

82.6 83.6 88.6 70.1 74.1 70.7 68.4 82.4 73.9 81.5 81.2 88.7 77.6

70.7 78.6 69.8 67.2 69.9 63.0 68.2 67.0 66.3 69.6 71.6 79.3 69.0

14.2 12.8 10.9 12.1 12.2 8.5 13.2 11.6 12.9 16.9 12.5 14.6 12.5

35.7 34.4 34.7 35.1 39.1 35.6 32.1 33.0 34.0 36.5 35.0 40.9 35.0

0.399 0.371 0.315 0.345 0.311 0.239 0.412 0.351 0.381 0.462 0.358 0.419 0.359

1.2

2.5

16.8

0.013

6.2

3.5

2.1

1.9

0.068

Treatments

LSD (0.05) Source of variation Year (Y) Genotype (G) Hybrids (H) Varieties (V) H vs. V YG CV (%)

351 d.f. Mean squares 1 9 3 5 1 9

18886626** 1121400** 867047** 1323180** 875561** 252249** 10.2

84.61** 9.83** 12.43** 6.25** 19.94** 3.81** 7.4

10646.41** 16.46** 11.15* 22.84** 0.51 17.01** 3.6

NUEbanthesis

NUEbmaturity

NUEs

Sw/Ns

Ns/Nt

156887.70** 0.030000** 8206.6** 13135.6** 1.449 4276.540** 1.503** 2074.90** 0.000444** 110.8** 54.3** 9.140** 6.992** 0.010** 11.15** 0.000330 117.6** 79.1** 9.262* 1.729 0.007* 22.84** 0.000600** 43.4* 20.3** 10.619** 11.517** 0.013** 18526.50** 0.000010 427.3** 149.9** 1.379 0.156 0.004 552.90** 0.000220** 69.2** 14.7** 7.304** 6.936** 0.006** 10.7 21.3 5.7 3.9 10.1 4.4 7.9

NUEb-anthesis, NUEb-maturity: nitrogen utilization efficiency for biomass production until anthesis and maturity, respectively; NUEs: nitrogen utilization efficiency for seed yield; Sw: seed dry weight; Ns: seed N; Nt: total aboveground N at maturity; *, ** significant at 0.05 and 0.01 probability level, respectively.

Seed nitrogen yield was significantly affected by years, genotypes and their interaction (Table 2). Seed N yield varied from 104.5 kg ha1 (Centennial) to 179.6 kg ha1 (GW 9003) in 1998 and from 28 kg ha1 (Centennial) to 66.9 kg ha1

(Demetra) in 1999. The over genotypes mean seed N yield was significantly higher in 1998 (145.5 kg ha1) compared to that in 1999 (43.3 kg ha1). This was the result of the higher seed yield as well as the higher seed N concentration obtained in 1998

Table 3 Contribution of the component trait to the resultant trait of 10 safflower genotypes grown in 1998 and 1999 Resultant trait

2

Y1 log seed N yield (g m ) Y2 log seed N content (g) per head

Y3 log NUEs (Sw/Nt)

Sxiyi/Syi 2

Component trait

X1 X2 X3 X4 X5 X6 X7

2

log seed yield (g m ) log seed N concentration (g g1) log seeds per head log seed weight (g) log seed N concentration (g g1) log(Sw/Nt) log(Ns/Nt)

1998

1999

0.528 0.472 0.586 0.011 0.425 0.207 0.793

1.028 0.028 0.833 0.178 0.011 0.015 0.985

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compared to 1999. Genotypes differed significantly in both seed N concentration and seed N yield. Orthogonal comparisons revealed that hybrids had higher seed N yield compared to varieties (101.4 vs. 89.8 kg ha1). The superiority of hybrids was due to the higher seed yield, because seed N concentration was similar to that of varieties (41.9 g N kg1 for hybrids vs. 42.1 g N kg1 for varieties). Analysis of the log of seed N yield (Y1) as a sum of the logs of seed yield (X1) and seed N concentration (X2) revealed differences in the magnitude of the contribution of each component to the variation in seed N yield among genotypes (Table 3). Seed yield was the most important component of seed N yield and its contribution to the total variation in seed N yield was at least 53%. The relative contribution of seed N concentration was 47% in 1998, while in 1999 it had no contribution, because of the negative correlation with seed N yield (data not shown). These results suggest that breeding for increased seed yield might be accompanied by an increase in nitrogen yield. Seed N yield was significantly correlated with seed N content per head in both years (r = 0.751, P < 0.05 in 1998 and r = 0.874, P < 0.01 in 1999). Seed N content per head could be further partitioned into seeds per head, seed weight and seed N concentration (Table 3). The contribution of seeds per head to the variation of seed N content per head among genotypes was the most important, accounting for 58.6% in 1998 and 83.3% in 1999. The values of the various nitrogen utilization efficiency parameters calculated in this study are given in Table 2. Nitrogen utilization efficiency for biomass production was generally higher in 1999 than in 1998. Averaged across genotypes, NUEb-anthesis was higher than NUEb-maturity in both years, meaning that NUE during the seed-filling period was lower compared with that during the vegetative period. Hybrids had, on average, significantly higher NUEb-anthesis and NUEb-maturity compared to varieties (69.2 vs. 63.7 and 56.2 vs. 52.9, respectively). The mean NUEs was similar for the two years (12.2 in 1998 vs. 12.5 in 1999), because the lower seed yield per unit seed N (Sw/Ns) in 1998 was compensated by the higher NHI (Ns/Nt) compared to 1999. Genotype differences were observed in NUEs with GW 9003, GW 9005, Tucson and C 9305 to have the highest values in 1998 and Demetra in 1999. NUEs was positively correlated with seed yield in both years (Fig. 1), indicating that high yield was probably associated with more efficient exploitation of nitrogen. Additional correlation analysis indicated that there was a negative correlation between NUEs and seed N concentration at maturity, significant for the first year only (r = 0.680, P < 0.05 in 1998 and r = 0.082, P > 0.05 in 1999). Moreover, when values of both years were included in the analysis, seed yield was significantly correlated with seed N concentration at maturity (r = 0.733, P < 0.01). These relationships suggest that high yield may be the result of better exploitation of nitrogen or high seed N concentration, and consequently, may be accompanied by low NUEs. Therefore, safflower breeders should select for both high yield and NUEs in order to ensure an improvement in both traits. Analysis of the log of NUEs (Y3) as a sum of the logs of seed yield per unit seed N (X6) and NHI (Ns/Nt) (X7) revealed differences between components in the magnitude of their

Fig. 1. Relationships between nitrogen utilization efficiency for seed production (NUEs) and seed yield for safflower in 1998 and 1999. Each relationship was based on means derived from 10 genotypes (n = 10).

contribution to the variation of NUEs among genotypes (Table 3). The relative contribution of NHI was much greater compared to that of Sw/Ns in both years, accounting for more that 79%. The differences in NUEs among genotypes followed generally those of NHI and could be explained taking into account the nitrogen translocation from vegetative tissues to the seeds during the seed-filling period (Koutroubas et al., 2004). Genotypes with high nitrogen translocation to the seeds showed also high NHI. It seems, therefore, that greater translocation increased the proportion of nitrogen partitioned to the seeds,

Fig. 2. Relationship between (leaf + stem) nitrogen concentration at maturity and nitrogen utilization efficiency for seed production (NUEs) in safflower. The relationship was based on means derived from 10 genotypes and two years of experimentation (n = 20).

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which in turn favoured high NUEs. NUEs was similar in hybrids and varieties (12.5 vs. 12.3) and this was the result of the similarity observed in both seed yield per unit seed N and in NHI. NUEs was negatively correlated with (leaf + stem) N concentration at maturity (Fig. 2), suggesting that low straw N concentration may be indication of higher NUEs. As it is shown by the coefficient of determination (r2), 47% of the variation in NUEs among genotypes could be explained by the variation in straw N concentration. In conclusion, the interrelations found among the various NUE-related traits suggest that using simple selection criteria to improve NUE of safflower might have negative implications on seed yield and quality. Therefore, evaluation and selection of different genotypes for NUE should be based on multiple criteria rather than just one criterion and also should be accompanied by evaluation for seed yield. Acknowledgements The authors wish to thank Dr. Mike Blanco (Global Agro) and Mr. Arthur Hill (Safftech) from USA and also Dr. Waedo Cero´n from Chile for providing safflower seeds as it is referred to Section 2. References Abel, G.H., 1975. Growth and yield of safflower in three temperature regimes. Agron. J. 67, 639–642. Abel, G.H., 1976. Effects of irrigation regimes, planting dates, nitrogen levels, and row spacing on safflower cultivars. Agron. J. 68, 448–451. Bassil, E.S., Kaffka, S.R., Hutmacher, R.A., 2002. Response of safflower (Carthamus tinctorius L.) to residual soil N following cotton (Gossypium spp.) in rotation in the San Joaquin Valley of California. J. Agric. Sci. 138, 395–402. Cazzato, E., Ventricelli, P., Corleto, A., 1997. Effects of date of seeding and supplemental irrigation on hybrid and open-pollinated safflower production in southern Italy. In: Corleto, A., Mu¨ndel, H.-H. (Eds.), Proceedings of the Fourth International Safflower Conference, Bari, Italy, 2–7 June, 1997, Adriatica Editrice. pp. 119–124. Corleto, A., Cazzato, E., Ventricelli, P., 1997. Performance of hybrids and openpollinated safflower in two different Mediterranean environments. In: Corleto, A., Mu¨ndel, H.-H. (Eds.), Proceedings of the Fourth International Safflower Conference, Bari, Italy, 2–7 June, 1997, Adriatica Editrice. pp. 269–275. Dajue, L., Mu¨ndel, H.-H., 1996. Safflower. Carthamus tinctorius L. Promoting the conservation and use of underutilized and neglected crops. 7. Institute of Plant Genetics and Crop Plant Research, Gatersleben/International Plant Genetic Resources Institute, Rome, Italy.

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