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a Unidad Integrada Facultad de Ciencias Agrarias (UNMdP), Estación Experimental Agropecuaria INTA Balcarce, C.C. 276, 7620 Balcarce, Argentina
b Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina)
c Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba C.C. 509, 5000 Córdoba, Argentina
* Corresponding author (laguirre{at}mdp.edu.ar).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: °C daf, °C d after flowering • NMR, nuclear magnetic resonance • PAR, photosynthetically active radiation
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Photosynthetically active radiation (PAR) intercepted by plants during the grain filling period (R6 to R9, Schneiter and Miller, 1981) largely determined oil concentration and weight per grain in the black hull hybrid Dekalb G-100 grown under adequate water and nutrient conditions (Andrade and Ferreiro, 1996; Dosio et al., 2000). Moreover, intercepted PAR from 250 to 450 degree days (°C d) after flowering (near the middle of the grain filling period, base temperature: 6°C) mainly accounted for weight per grain and oil concentration in the same black hull hybrid (Aguirrezábal et al., 2003). Merging their own experimental data with published and unpublished data from other agro-ecological regions, Ruiz and Maddonni (2006) found that normalized weight per grain follow a linear-plateau response with normalized postflowering source–sink ratios (calculated as the ratio between intercepted PAR and grain number per plant or leaf area duration and grain number per plant). In contrast, oil concentration was not related to changes in source–sink ratio in their work. Differences in the hybrid hull type were not considered in their analysis. The response of oil concentration to intercepted PAR during the whole grain filling period was, however, different for a black hull hybrid (Dekalb G-100) and a striped hull one (NKT). While the first increased oil concentration with intercepted PAR, the other remained unaffected for a range from 13.2 to 104.7 MJ per plant (Dosio et al., 2000). It is unknown whether such different responses are specific to the tested genotypes or if they are similar to other black hull or striped hull hybrids. The lack of response of the oil concentration when PAR intercepted by the striped hull hybrid was reduced (Dosio et al., 2000) would be a consequence of the lower level of intercepted PAR investigated in this work (the decrease of oil concentration when intercepted solar radiation decreased could be triggered by a lower level of intercepted PAR in striped hull hybrids than in black hull ones).
Investigating the dynamics of oil yield components during grain filling (e.g., Johnson and Tanner, 1972 for maize [Zea mays L.] weight per grain) could help to identify the underlying mechanism of variations in the final value of these yield components. Recent research characterized the dynamics of accumulation of oil weight and weight per grain in three genotypes with 30, 45, or 58% of oil potential concentration (Mantese et al., 2006) and under different source–sink relationships (estimated as leaf area duration per grain, Ruiz and Maddonni, 2006). In the black hull hybrid Dekalb G-100, the rate of accumulation of weight per grain decreased when intercepted PAR decreased (Andrade and Ferreiro, 1996). In the same hybrid, changes in grain oil concentration were linked to changes in the duration of the period when oil concentration linearly increased (Dosio et al., 1997). The effect of intercepted PAR on the dynamics of accumulation of weight per grain and oil concentration was never investigated in other hybrids. Growth rate of grains inserted on the periphery of the head tends to decrease following a 80% reduction in intercepted radiation during the early post anthesis period (R5.0 to R5.0+10 d) while the duration of the grain filling period showed the opposite trend (Lindström et al., 2006). Such type of compensation between rate and duration could explain the lack of response of oil concentration of the striped hull hybrid NKT when intercepted radiation was decreased (Dosio et al., 2000).
The objectives of this work were (i) to investigate the effect of intercepted PAR during grain filling on final weight per grain and grain oil concentration in several black hull and striped hull hybrids for a larger range of intercepted PAR per plant than that previously reported, and (ii) to analyze the variations in the dynamics of weight per grain and oil concentration under different intercepted PAR during grain filling. Special attention was paid to oil concentration responses to intercepted PAR since there is less information about it, as compared to weight per grain.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Experiments were designed to cover a wide range of (i) genotypes with black hull and striped hull grains, and (ii) intercepted PAR per plant during grain filling. Seven black hull hybrids and five striped hull ones, as well as an intercepted PAR ranging from 3.5 to 104.7 MJ per plant, were evaluated (Table 1 ).
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The black hull hybrid Dekasol 3881 and the striped hull one ACA 884 were sown at Balcarce (Exp. B1) and at Córdoba (Exp. B2) during the 1998–1999 and 1999–2000 growing seasons, respectively. Treatments to vary intercepted PAR per plant during the whole grain filling period consisted of (i) 80% shaded, (ii) 50% shaded, (iii) thinning to 50% of the original plant density, and (iv) untreated control.
The black hull hybrid Payé (KWS) and the striped hull one Paraíso 30 (Nidera S.A.) were sown at Balcarce during the 2002–2003 and the 2003–2004 growing seasons (Exp. C1 and C2, respectively). Treatments to vary intercepted PAR per plant were applied from 250 to 450°C d after flowering (base temperature: 6°C), the developmental period during which final weight per grain and oil concentration were best accounted for by intercepted PAR per plant (Aguirrezábal et al., 2003). Treatments consisted of (i) 80% shaded and (ii) untreated control.
The black hull hybrid Dekalb G-100, and the striped hull one Northrup King Tordillo were sown at Balcarce during the 1993–1994 (Exp. D) and 1995–1996 (Exp. E) growing seasons. Treatments to vary intercepted PAR per plant during the whole grain filling period consisted of (i) 50% shaded, (ii) thinning to 25% (Exp. D) or 50% (Exp. E) of the original plant density, (iii) 50% shaded + thinning, and (iv) untreated control. Further details about Exp. D and E are given in Dosio et al. (2000).
All experiments excluding B1 and B2 were designed as split plots with main plots completely randomized and three replicates (except for Exp. D with four replicates). Hybrids were assigned to main plots and treatments to subplots. Experiments B1 and B2 were designed as randomized complete blocks with four and three replicates, respectively. In all cases experimental units consisted of four rows 0.7 m apart and 6 m long.
Flowering of a plant was defined by the appearance of stamens in all florets from the outer ring of the capitulum (R5.1 stage, Schneiter and Miller, 1981). Flowering of a plot was registered when 95% of plants had flowered. Flowering occurred between 13 and 20 February in Exp. A1, between 18 and 23 January in Exp. A2, on 28 January in Exp. B1, on 26 January in Exp. B2, between 22 January and 1 February in Exp. C1, between 15 and 20 January in Exp. C2, on 10 February in Exp. D, and on 20 January in Exp. E.
Treatments were applied when 95% of the plants had their inner florets fertilized (after R6, Schneiter and Miller, 1981) in all experiments except for Exp. C1 and C2. Treatments were applied at 250°C d after flowering (R7) in Exp. C1 and C2. Shading treatments were achieved by using a uniform, black, synthetic, and neutral mesh cloth. Physiological maturity was taken as the day in which individual weight per grain did not increase compared to the previous sample (Exp. C, D, and E), or estimated visually (Exp. A and B), from the hard yellow color of the capitulum back face and from the brown color of its bracts (Farizo et al., 1982). Treatments ended at physiological maturity except in Exp. C1 and C2 in which treatments ended at 450°C d after flowering.
Measurements
Global daily incident radiation was measured with pyranometers (LI-200SB, LI-COR, Lincoln, NE) located 400 m (Balcarce) or 2000 m (Córdoba) from the experiments. The proportion of PAR intercepted by the crop as well as daily intercepted PAR per plant was measured as described by Dosio et al. (2000), in all hybrids in A1, B1, B2, C1, C2, D and E, and only in Dekasol 3881 and ACA 884 in A2.
Air temperature was measured with copper-constantan thermocouples (Thermoquar, Buenos Aires) in Balcarce experiments, and with thermistors (Stow Away XTI, ONSET, Computer Corporation, Pocasset, MA) in Córdoba experiments (except in Exp. A2). The sensors were cross-checked before the beginning of the experiments. Measurements were registered every 60 s, data were averaged every 3600 s and recorded with data loggers (Data Logger, LI-COR 1000; Delta-T DL2e Logger, Delta-T Devices Ltd., Cambridge, UK; or ONSET, Computer Corporation, Pocasset, MA). In Exp. A2 air temperature was obtained from a meteorological station placed 
8000 m away from the crops. Thermal time after flowering (0°C d after flowering) was calculated from air temperature using a base temperature of 6°C.
Weight per grain and grain oil concentration were periodically measured in Exp. B1 (hybrids Dekasol 3881 and ACA 884), Exp. D, and Exp. E (hybrids G-100 and NKT). Three to five capitula were sampled, oven-dried (air circulating at 60°C) up to constant weight, and weighed. Only nonempty grains (kernel occupying at least 20% of total space in the grain) were recovered. In all the experiments final nonempty grains were counted and weighed. Weight per grain was calculated as the quotient between the weight of all nonempty grains in each capitulum and its number. Oil concentration was measured by nuclear magnetic resonance (NMR) technique. Samples were dried in an oven at 60°C for 18 h and placed in dessicators with CaO. When they cooled to 23°C (Robertson and Morrison, 1979) their oil concentrations were determined with a NMR Analyzer Magnet Type 10 (Newport Oxford Instruments, Buckinghamshire, UK) in duplicate and averaged.
Kernel proportion in the grain and kernel oil concentration was determined in Exp. A1, A2, B1, and B2. Samples were prepared as a homogeneous grain mixture of the plants in each experimental unit. After mechanical dehulling, kernel oil concentration was measured by NMR as described for grain oil concentration. Kernel proportion in the grain was calculated in triplicate as Wk/(Wh + Wk), where Wk and Wh represented kernel and hull weight, respectively, considered in a dry base.
Data Analysis
Data were processed by analysis of variance procedures (General Linear Model Procedure; SAS Institute, 1988). When statistical differences were detected in more than one experiment, the highest P value is shown. Differences among means of treatment were evaluated with the Tukey test (P < 0.05). When treatment x hybrid interaction is not statistically significant (P > 0.05) the group means are presented with their significance; otherwise, the values for each hybrid and treatment are presented with their significance.
Two-step conditional models were used to determine the rate and duration of the linear increase phase for weight per grain and oil concentration from Exp. B1, D and E. The first step represented the weight per grain or grain oil concentration during its phase of linear increase: weight per grain (or oil concentration) = a + b x °C d after flowering (°C daf), for °C daf < c, and the second one the weight per grain (or oil concentration) during the stabilization phase: weight per grain or oil concentration = a + b x c, for °C daf > c, where a and b represented the intercept and the rate of the linear increase phase, and c was the unknown °C d after flowering where maximum weight per grain or oil concentration was reached. Duration of the oil concentration linear increase phase was considered as c – duration of the "lag phase" (an initial phase during which oil concentration slowly increased).
To study quantitatively the response of weight per grain and oil concentration to intercepted PAR during grain filling and to source–sink ratio data from different experiments were normalized as described by Ruiz and Maddonni (2006). Briefly, for each data set corresponding to a same hybrid in the same experiment, weight per grain, oil concentration, intercepted PAR during grain filling (the source), and intercepted PAR per grain (the source–sink ratio) were expressed in relative terms as: [(Xi – Xm)/Xm] where Xi is the individual value of each variable, Xm is the average of the variable in that hybrid across the different radiation treatments. Normalized data were adjusted to linear and linear-plateau (two-step conditional) models.
Grain oil concentration, kernel proportion in the grain and kernel oil concentration were expressed as a proportion of the maximum value. Linear regressions were performed on these normalized data.
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RESULTS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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0.01) among hybrids in A1 and A2. In general, striped hull hybrids presented a higher weight per grain than black hull ones (52.2 ± 9.4 mg vs. 42.6 ± 7.8 mg, average of control treatments) and no differences in the grain number between groups were observed (Table 2
). Oil yield per plant ranged from 6.5 to 36.3 g plant–1 among treatments, hybrids, and experiments. In Exp. A1, the hybrid x treatment interaction was statistically significant (P < 0.0001). Oil yield per plant in all the hybrids was different between shaded and thinned treatments (Table 2). In A2, the hybrid x treatment interaction was not statistically significant (P = 0.116). Shaded treatment presented a lower oil yield per plant than the control, and the thinned treatment showed a higher value than the control (Table 2).
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In A2, all hybrids, black or striped hull, reduced grain oil concentration when intercepted PAR was reduced by shading, and no differences were observed between thinned treatment and the control (Table 2). Highest differences among treatments were observed in black hull hybrids (mean difference between extreme values was 5.3 and 8.1 oil percentage points for striped hull and black hull hybrids, respectively). Grain number was mostly unaffected for variation in intercepted PAR in both black hull and striped hull hybrids, although in some cases shaded treatment showed a lower grain number than the control (Table 2). Most of the hybrids presented significant differences for weight per grain only between shaded and thinned treatments. In this experiment, mean incident PAR during grain filling was 8.1 ± 3.7 MJ m–2 d–1.
Low incident PAR during 10 consecutive days was registered in Exp. A2. Such a period started 13 d after the beginning of treatment application (data not shown). Mean incident PAR during this period was 4.2 ± 1.1, almost 50% lower than in the rest of the grain filling period. Such a cloudy period began at 240 and ended at 360°C day after flowering and partly overlapped the developmental interval 250 to 450°C d after flowering.
In Exp. C1 and C2, an 80% reduction of intercepted PAR during the period 250 to 450°C d after flowering highly reduced grain oil concentration in the black hull hybrid Payé and the striped hull hybrid Paraíso 30. Grains from control treatments were 20 and 13% heavier than shaded one in the black hull and the striped hull hybrid, respectively, in Exp. C1, and 24% and 26%, respectively, in Exp. C2 (Table 2). The grain number was affected by shading in the black hull hybrid, but not in the striped hull one (Table 2).
In B1 and B2, 80% shaded treatments registered lower values of intercepted PAR per plant during grain filling than those registered in A1, A2, and in previous works (Table 1). Even the black hull hybrid Dekasol 3881 or the striped hull one ACA 884 reduced grain oil concentration when intercepted PAR per plant was reduced (Table 2). Statistical differences were observed between thinned or control treatments and 80% shaded treatment (P < 0.0001), in both hybrids and experiments. In Exp. B2, differences were also significant between thinned or control treatments and 50% shaded one (Table 2). Maximum difference for this variable was observed in the black hull hybrid (17 percentage points, Exp. B). Although both hybrids were affected by intercepted PAR, the maximum grain oil concentration was reached at a lower level of intercepted PAR in the striped hull hybrid (around 20 MJ plant–1) than in the black hull one (around 40 MJ plant–1).
The treatment x hybrid interaction was not statistically significant for grain number, weight per grain, and oil yield per plant (P 
0.13) in Exp. B1 and B2. Increasing intercepted PAR per plant increased grain number from 825 to 1125 in B1 and from 748 to 1090 in B2 (P 0.002). Weight per grain increased from 39.8 to 52.5 mg in B1 and from 52.2 to 79.6 mg in B2 (P 0.002). In these experiments, variations up to 26 g of oil yield per plant were observed between thinned and 80% shaded treatment.
Reducing intercepted PAR during grain filling reduced oil yield per area in all the hybrids. However, striped hull hybrids tend to present higher oil yield per area than black hull ones even for the control (e.g., 1510 vs. 1281 kg ha–1 for striped and black hull hybrids, respectively, Exp. A1) or reduced levels of intercepted PAR during grain filling (e.g., 1128 vs. 806 kg ha–1 for striped and black hull hybrids, respectively, Exp. A1).
Relationships between Weight per Grain and Oil Concentration and Source and Source Sink Ratio for Black and Striped Hull Hybrids
When normalized data from all experiments were pooled, relative weight per grain and relative oil concentration showed a linear-plateau response to relative intercepted PAR during grain filling (r2 = 0.77 and r2 = 0.65, for weight per grain and oil concentration, respectively). The adjustments were not improved by linear functions compared to linear-plateau functions (r2 = 0.73 vs.0.77 and r2 = 0.53 vs. 0.65, for weight per grain and oil concentration, respectively). The relative source–sink ratio (intercepted PAR per grain) did not accounted for better than the source neither for relative weight per grain nor for oil concentration (r2 = 0.74 vs. 0.77 and r2 = 0.62 vs. 0.65, respectively).
The variability in relative weight per grain and in relative oil concentration were also better accounted for by the variability in the relative source than by the variability in the relative source–sink ratio when separate functions were adjusted to data corresponding to black hull and striped hull hybrids (data not shown). Relative weight per grain of both black hull and striped hull hybrids increased with a similar rate (0.30 ± 0.04 vs. 0.27 ± 0.04, respectively) up to relative intercepted PAR = 0.24 ± 0.10 and 0.33 ± 0.14 for black hull and striped hull hybrids (Fig. 1 ). Relative oil concentration increased with a higher rate (0.26 ± 0.05 vs. 0.20 ± 0.06) up to a higher relative source value (0.21 ± 0.13 vs. –0.03 ± 0.13) in black hull than in striped hull hybrids (Fig. 1).
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Kernel Proportion in the Grain and Kernel Oil Concentration
The higher grain oil concentration of black hull hybrids with respect to striped hull ones was mainly due to a higher kernel proportion in the grain (Table 5
, Exp. A1 and A2). Despite their lower kernel proportion, striped hull hybrids presented a higher weight per grain because they produce grains 13% heavier than black hull hybrids. Increasing intercepted PAR per plant increased kernel oil concentration even in black hull or striped hull hybrids (Table 6
). No effect of radiation treatments was observed on the kernel proportion in the grain, except for Morgan 734 and NKT in Exp A1 (Table 5).
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DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The level of intercepted PAR at which striped hull hybrids reach the maximum grain oil concentration is low compared to the typical values of intercepted PAR during grain filling in sunflower crops grown under potential conditions. These results could help to explain why oil concentration in striped hull hybrids is often considered as more stable to environmental changes than in black hull hybrids (V. Pereyra, President Biosol Semillas, Balcarce, Buenos Aires, Argentina, personal communication, 2007). The level of incident radiation needed to obtain a response in striped hull hybrids in experiments presented here rarely occurs in nature. It would be improbable that variations in incident solar radiation decrease oil concentration in striped hull sunflower crops grown under potential conditions. However, reductions in oil concentration in striped hull crops could be still possible under field conditions because of a low leaf area index during grain filling. Leaf area index during most of grain filling is often lower than the value needed to obtain a 95% interception of the incident solar radiation (2.5 to 3.0, Aguirrezábal et al., 1996, 2003) and other factors as hail, pests, and diseases could reduce it (e.g., Schneiter et al., 1987; Muro et al., 2001). Keeping a higher leaf area index during grain filling through crop management could help to obtain the maximum oil concentration with striped hull hybrids.
Genetic improvement in Argentina has directly or indirectly modified several traits related to yield, yield components and grain quality (López Pereira et al., 1999a, 1999b, 2000), including the increase in grain oil concentration (de la Vega et al., 2007), mainly by increasing kernel proportion in the grain (A. Vazquez, Sunflower Breeder, NIDERA Semillas S.A., Baigorrita, Buenos Aires, Argentina, personal communication, 2004). Results obtained in this work confirm this increase in grain oil concentration even in striped hull hybrids (e.g., the oil concentration of the hybrid Paraiso 30 in Exp. C1 and C2 attained values higher than 48%). Genetic improvement, however, does not seem to have affected the response of oil concentration to changes in intercepted radiation in striped hull and black hull genotypes. In our experiments, all black hull and striped hull hybrids showed the response described for each type of hybrid, independent of the year in which they where released to the market.
Both the rate and the duration of grain filling were affected by intercepted PAR. However, the rate of increase of oil concentration was markedly stable despite wide variations in intercepted PAR. In both black hull and striped hull hybrids, a decrease in intercepted radiation decreased final oil concentration mainly due to a reduction in the duration of the phase during which oil concentration linearly increases. Final oil concentration results from the relationships between the dynamics of weight per grain and oil weight per grain. A lower intercepted radiation decreased final oil concentration through an early detention of the phase during which oil is accumulated in a higher proportion than the rest of the chemical components of the grain. Such developmental process seems to be modulated by a decrease in intercepted radiation near the middle of grain filling (i.e., 250–450°C d after flowering, Aguirrezábal et al. [2003] and Exp. C1 and C2 in this paper). Interestingly, changes in duration of the phase during which oil concentration linearly increases also explained most of the differences in final oil concentration among black hull and striped hull hybrid (e.g., near 5 percentage points between oil concentration values of thinning treatment, Exp. B1). This agrees with Mantese et al. (2006) who observed similar results when studying the dynamics of accumulation of oil in three genotypes with 30, 45, or 58% of oil potential.
No compensation between rate and duration was observed neither for weight per grain nor for grain oil concentration. Compensation between rate and duration of leaf expansion has been identified as a common response in Arabidopsis thaliana (L.) Heynh. to different environmental stresses such as light, soil water deficit, and temperature (see discussion in Aguirrezábal et al., 2006). It has been also detected in growth of sunflower grains following an 80% reduction in intercepted radiation during the early post anthesis period (R5.0 to R5.0+10 d, Lindström et al., 2006). Based on these results, it could be suggested that compensation between variables underlying the dynamics of weight per grain could only be triggered by environmental stresses affecting the crop during initial stages of the evolution.
The kernel proportion in the grain was affected by treatments in both striped hull and black hull hybrids. These results disagree with our previous findings in one striped hull and one black hull hybrid (Santalla et al., 2002) and with assumptions that the kernel proportion in the grain is stable to environmental changes (e.g., Villalobos et al., 1996). The relationship between grain oil concentration and the kernel proportion in the grain was weak but significant for the black hull hybrid Dekasol 3881. However, oil concentration in the kernel was affected by intercepted radiation in most of cases. Oil concentration in the kernel was the only variable to account for variations in grain oil concentration in the hybrid ACA 884 while it largely explained most of the changes in the grain oil concentration (the proportion of variation accounted for by kernel oil concentration and kernel proportion in the grain were 92 and 13%, respectively) in hybrid Dekasol 3881. Although it is shown in this work that the kernel proportion in the grain is not insensitive to environmental changes its variation was very low. Changes in grain oil concentration following changes in intercepted radiation during grain filling largely depend on its effect on kernel oil concentration of both striped hull and black hull hybrids.
Weight per grain and oil concentration followed linear-plateau relationships with the source– sink relationship during grain filling. These results agree with results from Ruiz and Maddonni (2006). In this work, the source during grain filling was, however, a better explanatory variable than source–sink relationship of both weight per grain and oil concentration. Differences between our results and those from Ruiz and Maddonni (2006) probably arise from the main origin of source–sink variation during grain filling (the grain number and the leaf area per plant in the work of Ruiz and Maddonni, 2006, and the incident radiation in our work). Our results help us to better understand the validity domain of the source–sink relationships during grain filling as an explanatory variable of weight per grain and oil concentration in sunflower. The source is a better predictor than source–sink relationships when the crops are exposed to lower incident radiation during grain filling. In the land, such conditions are frequent in several regions in which sunflowers are grown (e.g., the cloudy period at Córdoba in Exp. A2 in this work). Interestingly, Ruiz and Maddonni (2006) did not find a relationship between source–sink and oil concentration. In this work, a relationship was found when all the data were pooled. Moreover, a clear difference in sensitivity was detected when normalized oil concentration of striped and black hull were separately related to both normalized intercepted variation and normalized source–sink relationships during grain filling. Differences between our results and those from these authors could be partly explained by the fact that we discriminated data by hull color. It is also probable that normalization applied by Ruiz and Maddonni (2006) could not account for slight differences among protocols of oil concentration measurement among different works (in our work all oil concentration data were measured in the same laboratory and by using the same protocol).
Contrary to the data described for grain oil concentration, in our experiments no clear differences were identified in the response of weight per grain to changes in intercepted radiation among black hull and striped hull hybrids. Critical periods for weight per grain and oil concentration were similar (Aguirrezábal et al., 2003) and both oil yield components showed similar responses to changes in source–sink relationships in the work of Ruiz and Maddonni (2006). These results suggest that the mechanisms involved in the determination of weight per grain and oil accumulation are, at least to some extent, unlinked. The behavior of grain number per plant was neither different among striped and black hull hybrids. Due to the similar behavior of grain number and weight per grain and the lower sensitivity of oil concentration to changes on intercepted PAR, oil yield per area tended to be similar or higher in striped hull hybrids than in black hull ones at low levels of intercepted PAR per plant suggesting that sowing striped hull hybrids could be considered when low radiation levels are expected.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication June 15, 2007.
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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