Competition in Variety Mixtures of Spring Wheat
SAMUEL KNAPP
Agroscope, Institute for Plant Production Sciences IPS, Reckenholzstrasse 191, 8046 Zürich, Switzerland, www.agroscope.admin.ch
mpetitive ability, intergenotypic competition
One way to deal with unpredictable growing conditions and pest pressure is to employ within crop diversity to achieve greater
major question is how to design this diversity. In this study the yield performance of a historic set of spring wheat varieties in monoculture and mixtures has been assessed. It was found that competitive ability is often reversed to monoculture yield. Plant height was identified
e strength. Progress in plant breeding for high monoculture yield has produced varieties that are smaller and of less competi implications of this reverse relationship for plant breeding and the identification of varieties for mixtures are discussed.
Mixtures of varieties are expected to be more resistant towards plant diseases and produce more stable yields across environm
monoculture stands. However, yields of mixtures often deviate from the expected yield calculated from the monoculture yields of the components. Besides the competition against weeds, crop plants in a monoculture stand are only exposed to intragenotypic competition; whe
f other varieties – intergenotypic competition. This additional type of competition leads to a different performance of a variety in a mixture and thus to deviation of the mixture yield from the expected yield.
mance under monoculture conditions and the choice of varieties for mixtures will rely on such varieties. Thus, the objective of this study was to assess the relation of monoculture performance and the competitive abiltiy in variet
Eight Swiss spring wheat varieties from the last 30 years have been grown in monoculture and in 50:50 mixtures with either th variety. In the mixture treatments varieties were separated in alternating rows (Erreur ! Source du renvoi introuvable.
and plots consisted of 6 rows with a distance of 17 cm and length of 2 m long. The trial was conducted at one site with 2 r monoculture treatments final plant height was measured and grain yield of the components was assessed by harvesting each row
Competitive ability (CA) of a variety was calculated as the yield of a variety in the mixture divided by half of the yield in monoculture as it is assumed that without any interaction or competition effects the expected yield in the mixture would be half of the monoculture yield. ). A
noculture and is thus a bad competitor.
The yields of the varieties in mixture showed a CA below 1, except in three cases (Erreur ! Source du renvoi introuvable. pronounced difference in CA between competing against variety Albis, which was released in 1983 and competing against variety
: Mixture plot where two varieties where grown in separate rows. Variety A in row 1, 3 and 5; variety B in row 2, 4 and 6
Figure 2: CA (CA) of seven varieties competing with the oldest variety, Albis, (red) and competing with the youngest variety, Digana, (blue) against the yield in
monoculture stand
Poster A8
www.agroscope.admin.ch,
One way to deal with unpredictable growing conditions and pest pressure is to employ within crop diversity to achieve greater stability. One y the yield performance of a historic set of spring wheat varieties in monoculture and mixtures has been assessed. It was found that competitive ability is often reversed to monoculture yield. Plant height was identified as a major mechanism for
e strength. Progress in plant breeding for high monoculture yield has produced varieties that are smaller and of less competitive ability. The discussed.
Mixtures of varieties are expected to be more resistant towards plant diseases and produce more stable yields across environments and years than lculated from the monoculture yields of the components. Besides the competition against weeds, crop plants in a monoculture stand are only exposed to intragenotypic competition; whereas plants in a mixture intergenotypic competition. This additional type of competition leads to a different mance under monoculture conditions and the choice of varieties for mixtures will rely on such varieties. Thus, the objective of this study was to assess the relation of monoculture performance and the competitive abiltiy in variety mixtures.
Eight Swiss spring wheat varieties from the last 30 years have been grown in monoculture and in 50:50 mixtures with either the oldest or the youngest ! Source du renvoi introuvable.). Plant density was 600 and plots consisted of 6 rows with a distance of 17 cm and length of 2 m long. The trial was conducted at one site with 2 replicates. In the monoculture treatments final plant height was measured and grain yield of the components was assessed by harvesting each row separately. by half of the yield in monoculture as it is assumed that without any interaction or competition effects the expected yield in the mixture would be half of the monoculture yield. ). A CA below 1 means that a
! Source du renvoi introuvable.There is a pronounced difference in CA between competing against variety Albis, which was released in 1983 and competing against variety Digana, which was
varieties competing with the oldest variety, Albis, (red) and competing with the youngest variety, Digana, (blue) against the yield in
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released in 2011: the varieties could much better compete against Digana than against Albis (Erreur ! Source du renvoi introuvable.). When competing against Digana there is a negative - although not significant – relationship between the monoculture yield and the CA of a variety, whereas this relationship can not be discovered when competing against Albis.
Plant height of a variety showed to have an impact on the CA: taller plants were better competitors against both Albis and Digana (Erreur ! Source du renvoi introuvable.). The year of registration showed a negative relation to the CA when competing against Digana but not when grown with Albis (Erreur ! Source du renvoi introuvable.). Younger varieties were worse in competitive strength in mixture.
To summarize, in competition with the variety Digana, the following three parameters are related to greater CA: (1) lower monoculture yield, (2) greater plant height and (3) earlier year of registration.
Figure 3: CA (CA) of seven varieties competing with the oldest variety, Albis, (red) and competing with the youngest variety, Digana, (blue) against plant
height in monoculture stand ( . = sign. at p<0.01)
Figure 4: CA (CA) of seven varieties competing with the oldest variety, Albis, (red) and competing with the youngest variety, Digana, (blue) against the year of
registration Discussion
With a perspective on breeding history, it can be concluded that progress in breeding for better monoculture yield has led to a decrease in intergenotypic CA. This could be due to the decrease in plant height, which has been shown here to have a strong impact on CA. Decrease in plant height is related to higher harvest index and thus less investment in vegetative growth. This can lead to greater yield in monoculture as more resources are left for generative growth and thus grain filling, which was proposed as a crop ideotype by Donald (1968). One implication of this negative relationship between monoculture and mixture performance is that in early screening steps in a breeding program the performance of lines in mixed stands (e.g. adjacent rows of different genotypes) can be reversed to their actual performance in a monoculture field (Goldringer et al., 1994).
However, in a competitive setting, which could be a mixture with other varieties or other species, or under strong weed pressure, this relationship can be reversed and investment in vegetative growth (great plant height or low harvest index) could pay off. The crucial trade-off will then be between the advantage of competitive strength versus the loss of resources through investment in vegetative growth. The threshold will depend on the amount of competition the crop will be exposed to.
One major obstacle in the design of variety mixture is the choice of the components. The fact that varieties with a higher CA yield better in a mixture than in monoculture does not necessarily justify that they are the best choice for well yielding mixtures as their increase in yield is often on the cost of the neighbouring variety. The reverse relationship of monoculture and mixture yield rather complicates the identification of components as the performance in a mixture is difficult to predict from merely monoculture performance. It could be suggested that for the design of variety mixtures varieties with similar height and thus similar CA should be selected in order to avoid suppression of weaker varieties. However, if superior performance - and particularly stability - of mixtures is due to compensation it could be of advantage that mixtures are composed of varieties of different height or CA (Creissen et al., 2013).
Evolution is based on natural selection and selects for strong competitors (Darwin, 1859). In sight of the reverse relationship of CA and monoculture yield, domestication and selection for harvestable population yield is thus detrimental to natural selection. Although natural selection for local adaptation, as it is the idea in “evolutionary plant breeding” (Döring et al., 2011), can produce a crop population which is adapted to local conditions but probably consists of strong competitors that invest too much resources in vegetative growth and competitive behaviour that are not available for grain filling and thus final yield (Denison, 2012).
References
Creissen, H.E., T.H. Jorgensen, and J.K.M. Brown. 2013. Stabilization of yield in plant genotype mixtures through compensation rather than complementation. Ann. Bot. 112(7): 1439–1447.
Darwin, C. 1859. On the Origin of Species.
Denison, R.F. 2012. Darwinian agriculture: How understanding evolution can improve agriculture. Princeton University Press. Donald, C.M. 1968. The breeding of crop ideotypes. Euphytica 17(3): 385–403.
Döring, T.F., S. Knapp, G. Kovacs, K. Murphy, and M.S. Wolfe. 2011. Evolutionary Plant Breeding in Cereals—Into a New Era. Sustainability 3: 1944–1971.
Goldringer, I., P. Brabant, and R.A. Kempton. 1994. Adjustment for Competition Between Genotypes in Single-Row-Plot Trials of Winter Wheat (Triticum aestivum). Plant Breed. 112(4): 294–300.
Session A Poster A9