PETRASEK, R.1
Key words: organic farming, winter wheat, weed, competitive ability
Abstract
In organic farming choice of suitable crop cultivars with the ability to suppress weeds eff ectively is a benefi cial cultural technique for weed control. In this context a study was conducted with winter wheat to determine the infl uence of growth dynamics and shoot morphology on competitive ability against weeds. A further intention was to identify parameters that contribute to this characteristic that may be considered in future breeding eff orts.
From 2004–2007 three fi eld experiments with various winter wheat genotypes were conducted. Aboveground wheat and weed biomass was destructively harvested at diff erent wheat developmental stages. Wheat leaf area was measured and biomass data were used to calculate growth rates. Wheat height development, leaf orientation and wheat as well as weed cover were assessed throughout the growth periods.
A high number of shoots in combination either with many or big leaves in spring and a rapid height growth at shooting were important. The development of a rather horizontal leaf structure in combination with a constant biomass development until fl owering proved advantageous. During wheat ear emergence a considerable genotypic variation in the eff ect on weed growth was observed.
In conclusion, our work identifi ed characteristics with a genotypic variation that may be used for the breeding of winter wheat varieties that are generally strong competitors.
Introduction
Due to the abandonment of herbicides weed control in organic farming is achieved by a combination of mechanical (e.g. mulching, thermal and biological treatments) and cultural practices (such as tillage, crop rotation, cultivation method). The latter include choice of suitable crop cultivars with the ability to eff ectively suppress weeds. In this context a study was conducted with winter wheat (Triticum aestivum L.) to determine the infl uence of growth dynamics and shoot morphology on competitive ability against weeds. Weed suppression proved to be a useful parameter in contrast to weed tolerance, because the ranking of the genotypes regarding weed suppression was detected as nearly stable throughout all examination years (e.g. Verschwele, 1994). Interspecifi c competition is a dynamic process that lasts the whole vegetation period.
1 BioForschungAustria, Rinnböckstrasse 15, 1150 Vienna, Austria,
Nevertheless, at some development stages of winter wheat a strong competitive ability is more important for an eff ective weed suppression.
Winter wheat is of particular importance for organic as well as for conventional farming systems. Signifi cant diff erences of winter wheat genotypes in weed suppression are well documented (e.g. Blackshaw, 1994). This genotypic potential, however, has not been utilised enough by farmers and breeders so far (Weiner, Griepentrog & Kristensen 2001).
In Austria, separate organic VCU (Value for Cultivation or Use) -test trials of wheat genotypes have been conducted by the Austrian Agency for Health and Food Safety (AGES) since 2002. In these trials new wheat parameters as leaf orientation and light perception are surveyed.
A further aim of our project was to detect additional wheat parameters, which improve weed competition and moreover may be considered in future breeding eff orts. These characteristics should be fast as well as easy to measure and should be highly heritable.
Materials and Methods
The fi eld experiments with various winter wheat genotypes were conducted in eastern Vienna, Austria (48°11´N, 16°31´E) in three vegetation periods from 2004 to 2007 in a fully-randomised plot experiment with four replicates. The soil type at this site ranged from loamy sand to sandy loam. The region is one of the driest in Austria with an average rainfall of 540mm per year. Winter and early spring conditions diff ered between the experiment years. The preceding crops were pea (2004 & 05) and potatoes (2006). Nitrate contents of the soil till 90 cm depths were between 136 kg/ha and 211 kg/ha in autumn and between 121 kg/ha and 288 kg/ha in spring.
Weed biomass was used as an indicator for the effi ciency of the wheat genotypes to suppress weeds. Emergence and growth of the natural weed fl ora of this habitat was not manipulated. Aboveground wheat and weed biomass was destructively harvested at diff erent wheat developmental stages (at the beginning and in the middle of shooting, ear emergence, the beginning of ripeness and maturation). Wheat leaf area was measured and biomass data were used to calculate growth rates. 2004/05 total weed biomass was sorted according to species or genus, for example Galium spp. and Stellaria media. Wheat height development and leaf orientation were assessed throughout the growth period. Wheat as well as weed cover density were quantifi ed at tillering.
Results and Discussion
The wheat genotypes varied in developmental dynamics of biomass, height and leaf area as well as in ground cover and leaf orientation. Total weed biomass and its dynamic diff ered in the various winter wheat genotypes (fi gure 1).
Weed biomass on the fi elds varied strongly between experimental years. At the beginning of wheat shooting no signifi cant genotypic diff erences in the amount of weed biomass were obtained (p=0,16). However, during wheat ear emergence a considerable genotypic eff ect on weed growth was observed (p=0,028). Weed suppression ability of the winter wheat genotypes was not dependent on yearly conditions. Thus, the amount of the aboveground weed biomass at ear emergence was found to best characterize the competitive ability of wheat genotypes against weeds.
An analysis of the complete dataset revealed that early development is one of the most important characters for competitive ability. This confi rms previous work on weed suppression by wheat (e.g. Coleman & Gill, 2003).
A high number of shoots in combination either with many or big leaves and a rapid height growth at shooting were similarly important. For an eff ective weed suppression it was further important for the wheat plants to remain strong competitors throughout the growing period until the end of fl owering. The development of a rather planophile (horizontal) leaf structure in
Figure 1: harvested weed biomass from 2004 to 2007 in winter wheat crop; bars represent mean weed dry matter at beginning of shooting (n=12), at ear emergence (n=10) and at maturation (n=8) of 5 winter wheat varieties. the error bars stand for the standard error of the mean. Signifi cant diff erences between means at ear emergence at the 5% level (Tukey-HSD) are indicated by diff erent letters.
Figure 2: Biomass development of weed species and total weed 2004/05; harvest times were at the beginning and in the middle of shooting, ear emergence and at the beginning of ripeness; data points represent arithmetic mean of 64 (1.& 4. harvest) and 32 (2.& 3.), respectively measured values in all wheat varitiety plots
combination with a constant biomass development until fl owering thus proved advantageous. For instance, a proportionally large increase in wheat biomass during tillering relative to subsequent growth resulted in more weed biomass at the beginning of wheat maturation. This reaction was strongly related to diff erences between weed species in their developmental dynamics during the vegetation period (fi gure 2). For example, Lamium amplexicaule was dominant at the beginning of shooting but disappeared towards ear emergence. In contrast, Galium spp. markedly increased in biomass at ear emergence and could thereby potentially outcompete wheat varieties that are only competitive in an early developmental stage.
The observed wheat parameters and the signifi cant developmental stages at which they should be measured (e.g. height at shooting, shoot number and vigour at the end of tillering), verifi ed by weed biomass, are mainly similar to the characteristic traits considered in the organic VCU-test trials of AGES (Oberforster et al. 2003).
Conclusions
In conclusion, our work identifi ed characteristics with a genotypic variation that may be used for the breeding of winter wheat varieties that are generally strong competitors. Nevertheless, the ecology of the weed fl ora or at least of the relevant weed species, the developmental dynamics – above and below ground – of winter wheat genotypes as well as the climate and soil conditions of a fi eld should be known and need to be considered for an eff ective weed control.
Acknowledgments
The preparation of this work would not have been possible without the support, hard work and endless eff orts of my colleagues at Bio Forschung Austria. Furthermore I would like to thank Franziska Löschenberger and her colleagues from “Saatzucht Donau” for designing the fi eld trials and their sustained interest. All work was funded by the Austrian Federal Ministry for Agriculture, Forestry, Environment and Water Management (project Nr. 1315).
References
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