The yields of the 4-10 highest-yielding varieties in the National Field Trials are by regression compared with the yield of eight corresponding reference varieties during 1980-2008. This
4 Breeding and genetics
Morten Haastrup 1), Per Gregersen 2) & Johannes Ravn Jørgensen 2)
1) Danish Agricultural Advisory Service (DAAS), Knowledge Centre for Agriculture
2) Aarhus University, Faculty of Agricultural Sciences (DJF), Department of Genetics and Biotechnology
4.1 Introduction
When analyzing the contribution of breeding and genetics to yield development in winter wheat over time, it is important to take into account the changes in conditions to which the development of new varieties have to adapt. The yield potential is a complex character that can be bred for in itself, but the realization of the potential will always be constrained by envi-ronmental limitations, such as nutrient availability and exposures to stress. There are two ma-jor cereal breeders in Denmark (Sejet Plant Breeding and Nordic Seed), and so the breeding of new winter wheat varieties is performed under national environmental and regulatory con-straints. Similarly, cultivars from abroad will usually be subject to Danish trial conditions before being sold on the Danish market.
The breeding efforts must adapt to changes in the aim of developing new, higher yielding varieties. The introduction of dwarf genes in 1987/88 follows this aim, but also introduces a switch from tall to very short wheat varieties. Discussions of utilization of nutrient and water resources in the soil during the 1990s turn the breeder to focus on varieties with larger root mass which implies varieties with more vegetative biomass causing taller varieties. Another factor leading to taller varieties during the 1990s was increasing disease incidents caused by Septoria. Taller plants appear to have lesser risk of fatal infection by this fungal disease. In-troduction of strobilurine fungicides in 1998 gives opportunity for extended grain filling pe-riod, and utilization of this yield potential may also be included in the breeding aim. The in-troduction of the Dutch variety Ritmo, which dominated the market in the late 1990s meant an increased tillering, also contributing to the total yield of the wheat plant. With a better resis-tance to Wheat Eyespot (Pseudocercosporella herpotrichoides) added, Ritmo has become the ancestor to all the new Danish varieties that dominate the market today.
Overall, there is a clear picture that the Danish breeding efforts during the last three decades have been modified to meet the challenges from the changes in growing conditions for winter wheat in Denmark. The aim of this paper is to assess whether these breeding efforts, in spite of the challenges, have kept up with the demand for sustained increases in yield potential of new winter wheat varieties.
4.2 Data and method
The yields of the 4-10 highest-yielding varieties in the National Field Trials are by regression compared with the yield of eight corresponding reference varieties during 1980-2008. This
regression analysis makes us able to estimate the improvement in yields contributed by the new high-yielding varieties. The total number of winter wheat varieties in the trials differed amongst years, but it increased considerably throughout the whole period. The fraction of high-yielding varieties (4, 7, or 10) represents c. 20 % of the total number of varieties in the trials. The variety composition of the highest-yielding varieties obviously changed from year to year; however, there was a clear tendency for many varieties to be included in this group for more years before being replaced.
The yields are an average of up to 10 national trials per year. Before 2004 the winter wheat varieties were tested in up to four trial series. Data from before 2004, when the introduction of alpha design enabled all trials to be joined in one series, is therefore adjusted by the trial ref-erence mixture to make a comparison between all years, trials, and varieties possible. The variety Hereward, which is used as reference for a long period (1992-2008) was only included in 5 of 10 trials from 2002. The trial reference mixture was used to correlate the yield between trial series and thereby enabling the comparison with the high yielding varieties in all the tri-als.
Year
1980 1985 1990 1995 2000 2005 2010
Grain Yield [85% DM, dt ha-1]
50 60 70 80 90 100 110
Figure 4.1 The yield of the 4-10 highest yielding varieties in test (bold line) compared to reference varieties (Kraka, Kosack, Sleipner, Pepital, Hereward, Ritmo, Hattrick and Smuggler) participating in national trials for several years (National Field Trials). The periods for reference varieties appear from Table 2.
In addition to the data from the National Field Trials, two minor trials focussing directly on the breeding effects on yield (yields of old varieties under comtemporary growing conditions) were included in the data analysis (an unpublished study from Nordic Seed 2007-2008, and Kjærsgaard et al. (2002)).
regression analysis makes us able to estimate the improvement in yields contributed by the new high-yielding varieties. The total number of winter wheat varieties in the trials differed amongst years, but it increased considerably throughout the whole period. The fraction of high-yielding varieties (4, 7, or 10) represents c. 20 % of the total number of varieties in the trials. The variety composition of the highest-yielding varieties obviously changed from year to year; however, there was a clear tendency for many varieties to be included in this group for more years before being replaced.
The yields are an average of up to 10 national trials per year. Before 2004 the winter wheat varieties were tested in up to four trial series. Data from before 2004, when the introduction of alpha design enabled all trials to be joined in one series, is therefore adjusted by the trial ref-erence mixture to make a comparison between all years, trials, and varieties possible. The variety Hereward, which is used as reference for a long period (1992-2008) was only included in 5 of 10 trials from 2002. The trial reference mixture was used to correlate the yield between trial series and thereby enabling the comparison with the high yielding varieties in all the tri-als.
Year
1980 1985 1990 1995 2000 2005 2010
Grain Yield [85% DM, dt ha-1 ]
50 60 70 80 90 100 110
Figure 4.1 The yield of the 4-10 highest yielding varieties in test (bold line) compared to reference varieties (Kraka, Kosack, Sleipner, Pepital, Hereward, Ritmo, Hattrick and Smuggler) participating in national trials for several years (National Field Trials). The periods for reference varieties appear from Table 2.
In addition to the data from the National Field Trials, two minor trials focussing directly on the breeding effects on yield (yields of old varieties under comtemporary growing conditions) were included in the data analysis (an unpublished study from Nordic Seed 2007-2008, and Kjærsgaard et al. (2002)).
4.3 Analysis
If the yields of the reference varieties decreased over years due to e.g. break-down of the dis-ease resistance, the slope of the regression of yield on year for each indivual reference variety should be negative. However, table 1 shows that none of the reference varieties had a statisti-cally significant tendency to a higher or lower yield over the years. On the other hand, the highest-yielding varieties significantly increase in yield over years.
Table 4.1 Annual yield increase for reference varieties.
Variety Slope [dt/ha/y] P value
Kraka 0.41 0.37
Kosack 0.04 0.87
Sleipner -0.04 0.96
Pepital -0.30 0.73
Hereward -0.14 0.59
Ritmo 0.01 0.97
Hattrick -1.03 0.33
Smuggler 0.23 0.89
4-10 highest yielding 0.93 <0.001
For the span of years covered by each individual reference variety a regression analysis was made for the relative yield of the 4-10 highest-yielding varieties. This showed that the relative yield of the 4-10 highest-yieldning varieties increased significantly when compared to all ref-erence varieties but Smuggler (Figure 2 and Table 2). From Figure 2, it is evident throughout the whole period that the yield of the high-yielding varieties was equal to the yield of the ref-erence variety at the time it was adobted as refref-erence, but that the group of high-yielding va-rieties gradually out-competes the reference variety when new high-yielding vava-rieties enter the group of 4-10 highest yielding varieties. The slopes do not differ significantly amongst the different reference varieties. The new and highest-yielding varieties contributed with an aver-age yield improvement of 1.1 % per year (1980-2008). This corresponds to an improvement of yield between 82 and c. 100 kg per hectare per year in comparison with the mean yield of the reference varieties in the period.
In a study on yields of old varieties under comtemporary growing conditions, two years’ trials at the Nordic Seed breeding station near Odder showed an improvement in yield correspond-ing to 0.5 % per annum, when the old variety Kraka was compared to the current reference mixture (4 varieties), which is also used as reference mixture in the national yield trials. But with the 10 highest-yielding varieties in the national yield trials doing around 3 % better than the same reference mixture in the same two year period, the improvement per year since Kra-ka might in fact be a bit better, with an estimated improvement corresponding to 0.6 % per annum. Kjærsgaard et al. (2001) found the same improvement in yield per annum, when comparing the variety Kraka to the twelve year younger variety Ritmo in trials at Sealand. In
4.3 Analysis
If the yields of the reference varieties decreased over years due to e.g. break-down of the dis-ease resistance, the slope of the regression of yield on year for each indivual reference variety should be negative. However, table 1 shows that none of the reference varieties had a statisti-cally significant tendency to a higher or lower yield over the years. On the other hand, the highest-yielding varieties significantly increase in yield over years.
Table 4.1 Annual yield increase for reference varieties.
Variety Slope [dt/ha/y] P value
Kraka 0.41 0.37
Kosack 0.04 0.87
Sleipner -0.04 0.96
Pepital -0.30 0.73
Hereward -0.14 0.59
Ritmo 0.01 0.97
Hattrick -1.03 0.33
Smuggler 0.23 0.89
4-10 highest yielding 0.93 <0.001
For the span of years covered by each individual reference variety a regression analysis was made for the relative yield of the 4-10 highest-yielding varieties. This showed that the relative yield of the 4-10 highest-yieldning varieties increased significantly when compared to all ref-erence varieties but Smuggler (Figure 2 and Table 2). From Figure 2, it is evident throughout the whole period that the yield of the high-yielding varieties was equal to the yield of the ref-erence variety at the time it was adobted as refref-erence, but that the group of high-yielding va-rieties gradually out-competes the reference variety when new high-yielding vava-rieties enter the group of 4-10 highest yielding varieties. The slopes do not differ significantly amongst the different reference varieties. The new and highest-yielding varieties contributed with an aver-age yield improvement of 1.1 % per year (1980-2008). This corresponds to an improvement of yield between 82 and c. 100 kg per hectare per year in comparison with the mean yield of the reference varieties in the period.
In a study on yields of old varieties under comtemporary growing conditions, two years’ trials at the Nordic Seed breeding station near Odder showed an improvement in yield correspond-ing to 0.5 % per annum, when the old variety Kraka was compared to the current reference mixture (4 varieties), which is also used as reference mixture in the national yield trials. But with the 10 highest-yielding varieties in the national yield trials doing around 3 % better than the same reference mixture in the same two year period, the improvement per year since Kra-ka might in fact be a bit better, with an estimated improvement corresponding to 0.6 % per annum. Kjærsgaard et al. (2001) found the same improvement in yield per annum, when comparing the variety Kraka to the twelve year younger variety Ritmo in trials at Sealand. In
comparison, Öfversten et al. (2004) found, on the basis of the Finnish statutory variety test, that new varieties contributed to an annual yield increase of 0.63 % in winter wheat and 0.97
% per anno in winter rye.
Year
1980 1985 1990 1995 2000 2005 2010
Grain Yield relative to Reference [%]
90
Figure 4.2 Yield of the 4-10 highest yielding varieties in the national field trials relative to the refer-ence varieties (Kraka, Kosack, Sleipner, Pepital, Hereward, Ritmo, Hattrick and Smuggler) covering different periods (National Field Trials). The periods for reference varieties appear from Table 2.
Table 4.2 Relative annual yield increase of 4-10 higest yielding varieties.
Reference
Hereward 1992-2008 1.09 <0.001 80.9 89
Ritmo 1992-2006 0.85 <0.001 87.8 97
Hattrick 2000-2008 1.39 0.005 90.5 100
Smuggler 2002-2008 0.79 0.260 92.4 102
Mean 1.1 92
This analysis is based on yields of winter wheat varieties in well-conducted trials in the period 1980-2008. How these yields translate into the yields of common Danish agriculture during the same period is another question, to which the answer depends, first of all, on the choice of varieties by the farmers and also on common agricultural practices. Based on the amounts of
comparison, Öfversten et al. (2004) found, on the basis of the Finnish statutory variety test, that new varieties contributed to an annual yield increase of 0.63 % in winter wheat and 0.97
% per anno in winter rye.
Year
1980 1985 1990 1995 2000 2005 2010
Grain Yield relative to Reference [%]
90
Figure 4.2 Yield of the 4-10 highest yielding varieties in the national field trials relative to the refer-ence varieties (Kraka, Kosack, Sleipner, Pepital, Hereward, Ritmo, Hattrick and Smuggler) covering different periods (National Field Trials). The periods for reference varieties appear from Table 2.
Table 4.2 Relative annual yield increase of 4-10 higest yielding varieties.
Reference
Hereward 1992-2008 1.09 <0.001 80.9 89
Ritmo 1992-2006 0.85 <0.001 87.8 97
Hattrick 2000-2008 1.39 0.005 90.5 100
Smuggler 2002-2008 0.79 0.260 92.4 102
Mean 1.1 92
This analysis is based on yields of winter wheat varieties in well-conducted trials in the period 1980-2008. How these yields translate into the yields of common Danish agriculture during the same period is another question, to which the answer depends, first of all, on the choice of varieties by the farmers and also on common agricultural practices. Based on the amounts of
certified sowing seeds sold, as reported by the Danish Plant Directorate every year
(www.pdir.dk), there is a lag of at least four years from their first appearance in the National Field Trials until new high-yielding varieties get their break-throughs as commonly grown varieties. Furthermore, the choice of varieties can be based on other reasons than pure yield, for example quality or disease resistance. For instance, the sowing seed data shows that in the year 2002 the share of sowing seeds from varieties that in previous years had been part of the group of high-yielding varieties, as defined in this analysis, had fallen to a minimum of around 50 %. After 2006, the high-yielding varieties have comprised more than 90 % of the sowing seed sold, and it seems that the new and taller winter wheat varieties with a presuma-bly better ability to take up nitrogen are gaining importance in common agricultural practice.