Abstract

Keywords

Introduction

Oilseed rape (Brassica napus L.) is an important crop to diversify cereal dominated crop rotations. However, oilseed rape has a relatively poor nitrogen (N) efficiency (Aufhammer et al. 1994, Schjoerring et al. 1995). In order to obtain maximum seed yield, high rates of nitrogen fertilizer have to be applied. Moreover, the relatively small recovery of applied nitrogen in the seed involves risks for leaching of nitrogen to the groundwater (Lickfett 1993). Breeding in improved efficiency for uptake and utilization of nitrogen has never been done in this crop. The aim of this study is to investigate the genetic variation in N efficiency in a genetically broad material of winter oilseed rape and classify the genotypes in their response to N application (responder or non responder) and their efficiency. Efficiency means realizing high grain yield under nitrogen deficiency (Sattelmacher et al. 1994).

Materials and methods

Ninety genotypes from five different groups have been tested: 44 present European breeding lines, 15 hybrids, 15 old land varieties, 13 resyntheses (crosses between Brassica campestris and Brassica oleracera) and 3 crosses between Falcon msl (male sterility Lembke) and resyntheses) They were investigated under field conditions 1998 at the location Einbeck in Northern Germany. The experiment was performed with two N treatments, two replications and plot sizes of 7,9 m². N fertilizer was given in a ‘high’ (240 kgN/ha) and a ‘reduced’ (0 kgN/ha) treatment.

Several characters which possibly are related to N efficiency were evaluated: date of flowering, chlorophyll content, plant height, fresh weight, dry weight, seed yield, N amount in the seeds, straw yield and N amount in the straw, N content in dropped leaves, oil and glucosinolat content in the seed. The harvest indices and the N harvest indices were calculated.

To get the N content in dropped leaves, the leaves freshly dropped during two days were collected at each N supply and dried at 60°C. N, oil and glucosinolat contents were measured with NIRS (near-infrared-reflectance-spectroscopy) (Reinhardt 1992).

Results

All characters showed significant genotype reaction, but there are no significant interactions between genotype and nitrogen application except N content in the biomass at beginning and end of flowering and glucosinolat-content.

Fig.1: Grain yield at two N levels 0 and 240 kg N/ha

The genotypes can react to N supply in four different ways (see Fig.1): efficient or non-efficient according to the grain yield under N deficiency and responder or non-responder according to the grain yield increase due to N application. A subdivision in genotype groups for this character can be made. The resyntheses were always non-efficient, but their crosses with Falcon (Falcon msl x resyntheses) were efficient. The response on N application was different in the genotype groups, only the group of resyntheses have shown no response on N supply.

Uptake efficiency can be characterized by N yield of the overground biomass. For this character no clear grouping can be observed (Fig.2). The resyntheses have shown low grain yields and therefore they have not so much N/ha in the seeds, but the total N yield is not so far away from the other groups, so that there must be more N in the straw.

Fig.2: N yield of the overground biomass (kg N/ha) at two N levels 0 and 240 kg N/ha

Fig.3: N harvest indices at two N levels 0 and 240 kg N/ha

The N harvest index shows the utilization efficiency of the genotypes. Without N supply the N harvest index is higher than at high N supply, indicating a better utilization efficiency (Fig.3).

The hybrids, lines and old land varieties were not separated as groups, only most of the resyntheses shows a poor utilization efficiency.

Fig.4: N content in dropped leaves at two N levels 0 and 240 kg N/ha

N content of dropped leaves showed a large variation at both N levels and is specific for each genotype (Fig.4). No general difference can be observed among genotype groups. This results are in agreement with the results from a similar study at two locations in 1997 (Kessel and Becker 1999).

Conclusion

Breeding strategies for improved N efficiency can be based on selection for low N content in dropped leaves and for high N harvest index. In this experiment the N harvest index was calculated only from overground biomass not including roots and dropped leaves. The contributions of roots, dropped leaves and other physiological aspects are under investigation.

This experiment will be continued at several locations under different climatic conditions.

Acknowledgments

We thank the DFG – Deutsche Forschungsgemeinschaft – for financial support and the KWS – Kleinwanzlebener Saatzucht AG Einbeck - for carrying out the field trials. There are special thanks to Novartis Seeds GmbH for supporting the participation of the presenting author at the International Rapeseed Congress 1999.

References

Aufhammer, W., Kübler, E. und Bury, M. 1994: Stickstoffaufnahme und Stickstoffrückstände von Hauptfrucht- und Ausfallrapsbeständen. J. Agronomy & Crop Science 172, 255-264

Kessel, B. and Becker H.C. 1999: Genetic variation of nitrogen-efficiency in field experiments with oilseed rape (Brassica napus L.). Proceedings of the Sixth International Symposium on Genetics and Molecular Biology of Plant Nutrition, Denmark (in print)

Lickfett, T. 1993: Auswirkungen verminderter Produktionsintensität in zwei Rapsfruchtfolgen auf Elemente des N-Haushaltes im System Boden-Pflanze. Diss., Göttingen

Reinhardt, T.-C. 1992: Entwicklung und Anwendung von Nah-Infrarot-spektroskopischen Methoden für die Bestimmung von Öl-, Protein-, Glucosinolat-, Feuchte- und Fettsäure-Gehalten in intakter Rapssaat. Diss., Göttingen

Sattelmacher, B., Horst, W.J. and Becker, H.C., 1994: Factors that contribute to genetic variation for nutrient efficiency of crop plants. Z. Pflanzenernähr. Bodenk. 157, 215-224

Schjoerring, J.K., Bock, J.G.H., Gammelvind, L., Jensen, C.R. and Mogensen, V.O. 1995: Nitrogen incorporation and remobilization in different shoot components of field-grown winter oilseed rape (Brassica napus L.) as affected by rate of nitrogen application and irrigation. Plant and Soil 177, 255-264