Browsing by Subject "Volunteer"

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Genotypische Variation der Überdauerungsneigung von transgenem und konventionell gezüchtetem Raps und Möglichkeiten der Beeinflussung durch Bodenbearbeitung als Beitrag zur Sicherheitsforschung bei transgenen Kulturpflanzen
(2004) Gruber, Sabine; Claupein, Wilhelm
High losses during harvesting of oilseed rape in combination with secondary dormancy of the seeds can result in a large soil seed bank which may persist for several years. Volunteers emerging from this seed bank cannot be controlled completely, particularly when they develop in another rapeseed population. In addition to well known agricultural problems, the risk of temporal and spatial gene dispersal by persistent seeds and volunteers gets more significant. With regard to genetically modified (GM) cultivars, seed dormancy and persistence of oilseed rape volunteers have to be reconsidered. The aim of the current study was to investigate the chances for a reduction of seed persistence and gene dispersal by growing specific genotypes and by the implementation of appropriate tillage operations. Four publications describe and discuss experiments in the laboratory and the field on the aspects ?genotype? and ?soil tillage?. One central point was the characterisation of the genotypic variation of secondary dormancy and seed persistence in GM (herbicide tolerant) and conventionally bred oilseed rape. A gradual approach towards field conditions was performed by three experiments. The first experiment examined potential seed persistence by artificial induction of secondary dormancy in the laboratory. The second experiment was a burial of seeds in the soil for six months on a field. The third experiment examined persistence of seeds actually lost during harvest and exposed afterwards to different tillage operations in a field experiment. All three experiments showed a high genotypic variability in seed dormancy and persistence. In the laboratory the level of secondary dormancy of conventional cultivars was a total of 3?76% and of the GM cultivars 1?31%. The number of persistent seeds in the burial experiment was 7?90% in the conventional and 12?79% in the GM assortment. Seeds from the seed rain of the four conventionally bred cultivars in the field experiment persisted in the soil from 0?11% over six months. A significant, positive correlation was found between the laboratory results for cultivars from two crop years as well as between the results from laboratory and burial experiments. This is an indication for a genetic background of seed dormancy and persistence of oilseed rape. It has been demonstrated that a laboratory method for induction of secondary dormancy can describe differences of seed persistence in the field. This result gives a chance for screening new cultivars in the laboratory to identify desired, low persistent genotypes. The other focus of the study was the effect of various tillage treatments on seed persistence and seedling recruitment in the field. Four differently intensive tillage operations incorporated the seeds of two near-isogenic cultivars at different times and soil depths, or left the soil untilled. Winter wheat was sown as following crop in all treatments whereby no weed control was performed. The highest number of seeds generally entered the soil seed bank when seeds were incorporated into the soil by stubble tillage immediately. After six months 1?14% of the initial seed input was found again in the soil in these treatments, and in one isolated case about 28%. Delaying the stubble breaking, the soil seed bank was 0?3%. Leaving the seeds undisturbed on the soil surface until direct drilling resulted in a soil seed bank of 0?17%. Therefore, the first tillage operation after harvest of oilseed rape should be performed with some time delay to avoid large soil seed banks. Soil inversion by a mouldboard plough shifted the majority of seeds into deep soil horizons from where a successful germination was restricted. In contrast, primary tillage by a rigid tine cultivator or zero tillage mainly distributed the seeds within the upper soil layer. Thus the number of flowering volunteers in the first spring was highest in these treatments, with a maximum of one volunteer m-2. Gene dispersal from oilseed rape volunteers to other rape crops and feral relatives was possible because their flowering periods overlapped. The volunteers were able to produce viable seeds, despite high levels of damage by pests and diseases. Overall, a high genotypic variability was found for seed persistence of oilseed rape. Tillage operations, particularly the time of stubble tillage, can also influence seed persistence and the occurrence of volunteers. Combined with a thorough knowledge of the processes involved, the selection of low persistent genotypes and adequate tillage operations offer chances to limit or even to avoid undesired gene dispersal from oilseed rape volunteers, and to make gene dispersal a predictable factor.
Management of volunteers derived from imidazolinone-tolerant oilseed rape
(2016) Huang, Shoubing; Claupein, Wilhelm
Oilseed rape (OSR) has become the second most important oilseed crop after soybean worldwide, producing 70.95 million tons of seed yield, and providing 13.4% of world supply of oilseeds in 2014. The demand for OSR is expected to increase due to protein meals/cakes used in animal feed and vegetable oils/fats for biodiesel and human consumption. With increasing cultivation area, concern over volunteer OSR is rising, particularly if the variety in question is tolerant to specific herbicides. Currently, the introduction of imidazolinone-tolerant OSR (commercially named Clearfield® OSR; CL OSR) into Europe poses new challenges for chemical control of CL OSR volunteers because of their tolerance to imidazolinone herbicides and other acetolactate synthase (ALS) inhibiting herbicides. Additionally, the potential of gene dispersal in time and space by persistent dormant seeds in the soil and by volunteers is increasing. Volunteers emerge from the soil seed bank, the volume of which is predominantly dependent on seed dormancy. Therefore, the objectives of this study were (i) to investigate seed dormancy and dormancy formation of CL OSR, and (ii) to find out suitable agricultural strategies to reduce volunteers by growing OSR genotypes with low potential for seed dormancy and seed survival, and by implementing appropriate tillage operations. Focusing on these aims, several experiments were carried out with different methods, namely field experiments, germination tests in the laboratory, and genomic analysis, providing data for three scientific articles. Experiment 1. A 3-year field trial in south-west Germany investigated dormancy dynamics during seed development (primary dormancy and potential secondary dormancy; tested with an existing standard method in the laboratory) of 10 non-CL OSR varieties (lines) in 2009 and 2010, and of five CL OSR varieties (hybrids) in 2014. Experiment 2. A total of 15 CL OSR genotypes grown at two locations in south-west Germany in 2012/2013, and eight genotypes (two CL genotypes included) grown at 12 locations across Germany in 2011/2012, were tested for potential secondary seed dormancy with the aim to investigate dormancy traits of CL OSR and maternal environmental effects on dormancy formation. Experiment 3. A 5-year experiment (2011–2015) was conducted in south-west Germany with non-CL OSR and CL OSR (two CL varieties: high dormant and medium dormant) in the same rotation (non-CL winter oilseed rape - winter wheat - CL winter oilseed rape - winter wheat - corn) to investigate OSR volunteer dynamics under different modes of tillage (inversion tillage, non-inversion tillage, no-till, with or without additional stubble tillage prior to primary tillage). Following hypotheses were tested: Experiment 1. (i) There is primary (innate) and secondary (induced) dormancy in oilseed rape; (ii) primary dormancy decreases during seed development, the potential secondary dormancy increases; (iii) at maturity, the level of the remaining primary dormancy and the varietal potential to secondary dormancy correlate. These hypotheses have been approved. Primary dormancy decreased from a high dormancy level (ca. 99%) at about 30 days after flowering (DAF) to a quite low level (< 15%) at late seed development. Embryo growth probably regulates the dynamics of primary dormancy, at least during early seed development. Depending on variety and year, potential secondary dormancy initially increased from nearly 0% to the highest level (up to 90%) at about 70 DAF, and then slightly decreased with further seed development. The correlation between primary dormancy and potential secondary dormancy was high at early seed development, but was quite low at late seed ripening. Experiment 2: (i) There is variation in potential seed dormancy of CL OSR; (ii) F1 (seeded) and F2 (harvested) generations of hybrid CL-OSR show similar dormancy levels although changes through environmental effects are known; (iii) the environment (location) during seed development and maturation has an effect on the potential dormancy. The hypotheses were approved. The CL OSR genotypes differed in potential secondary dormancy from 0.0 to 95.7% in the F1 generation and from 3.5 to 77.9% in their corresponding offspring (F2). Out of the 15 CL genotypes, nine were considered to be low dormant (<30% dormancy level). High correlation (r = 0.96) between F1 and F2 generations indicates a strong inheritance of seed dormancy. Precipitation during seed development is thought to be a contributor to dormancy formation, e.g. the higher the precipitation the higher the dormancy level. These results indicate that selection or breeding for low dormancy CL OSR is feasible. A direct comparison of varieties by dormancy is only possible if they have been grown and harvested at the same location, due to environmental effects. Experiment 3: (i) The soil seed bank size of OSR is determined by post-harvest tillage (particularly tillage time) and seed dormancy traits of the cultivated variety; (ii) the emergence of volunteers from the seed bank also depends on the mode of tillage; (iii) gene segregation in herbicide-tolerance might occur among CL volunteers. These hypotheses were partly approved. There was no significant effect of tillage on the soil seed bank, but the soil seed bank was visibly higher if stubble tillage was done prior to primary tillage (179 vs. 56 seeds m-2; treatments with stubble tillage vs. corresponding treatments without stubble tillage). There were significant effects of tillage in general on volunteers in the next crop. Non-inversion tillage resulted in 30 times more volunteers in the following winter wheat crop than inversion tillage due to shallow seed burial depth. A high dormancy OSR variety resulted in a significantly larger soil seed bank than a medium dormancy variety (147 vs. 58 seeds m−2) but in fewer volunteers (0.9 vs. 1.9 volunteers m−2) in the first following crop winter wheat, probably due to slow release of seeds from dormancy. Hypothetically speaking, seeds from low dormancy varieties seem to be released from dormancy more rapidly than seeds from high dormancy varieties. Gene segregation with 10 zygosities of the imidazolinone-tolerance genes PM1 and PM2 was detected in the CL volunteers in the first following crop winter wheat. Approximately 90% of sampled plants were homozygous for PM1 and PM2, still conferring a high tolerance to imidazolinones. Overall, a high variation in potential secondary dormancy was detected for CL OSR, which is similar to non-CL OSR. The contribution of seed dormancy to the soil seed bank was confirmed. During seed development, maternal environment can influence seed dormancy dynamics to some extent. Tillage operations, particularly tillage time, can also influence the soil seed bank and the emergence of volunteers. A very new aspect is that the disposition of seeds to release from dormancy (instead of induction of dormancy) should be considered in further studies. Sound strategies to control volunteers should include (1) the use of low dormancy varieties with a low potential to establish a seed bank and with a fast release from dormancy, and (2) a combination of different tillage operations in the years following OSR cultivation, e.g. delayed inversion tillage with a deep burial depth in the first year, followed by shallow non-inversion tillage in subsequent years. Combined with a thorough knowledge of seed dormancy, of the development of the soil seed bank and of the release from dormancy, the occurrence of CL volunteers in following crops can be reduced or even avoided by a scope of practical methods and approaches proposed in this study.
Untersuchung alternativer Unkrautmanagementsysteme für Kulturraps unter Einbeziehung von Möglichkeiten zur Reduzierung des Auftretens von Raps als Durchwuchs
(2022) Schwabe, Sebastian; Claupein, Wilhelm
Oilseed rape is the worlds second most important oil crop after soybeans. In the course of the European Green Deal of the European Union and the associated stronger promotion of renewable energies in the future, it can be assumed that the importance of oilseed rape cultivation will continue to increase. Due to the price pressure on conventional farms in Germany, cultivation systems have been changed from an economic point of view, partly to the detriment of sustainability. As a re-sult, crop rotations often consist of a few monetarily profitable crops and the proportion of spring crops in the crop rotation is reduced. Oilseed rape cultivation is attractive from an economic point of view, and its share in the crop rotation has been increased. The intensity of tillage and mechanical weed control has been reduced. The weed control success is strongly dependent on the effectiveness of numerically limited herbicidal active agents. Due to monotonous crop rotations and the lower tillage intensity, certain weed species are pro-moted more strongly, while at the same time these are controlled with only a few herbicid-al active agents. Adapted, difficult-to-control, and in some cases herbicide-resistant weed populations develop. For this reason, the purpose of this thesis is to evaluate alternative weed management systems in oilseed rape, while also investigating options for prophylac-tic prevention of the emergence of volunteer oilseed rape as a weed in crop rotation. The objectives of this thesis were: (i) To evaluate the feasibility of hoeing as a mechanical weed control method and the application of the Clearfield® system in oilseed rape as a comparison to common, field herbicide strategies. (ii) To focus on the volunteer oilseed rape issue. Volunteers resulting from Clearfield® oilseed rape are more difficult to control chemically in subsequent crops due to inherited herbicide tolerance. The potential of differ-ent seed treatments in oilseed rape to reduce the development of secondary dormancy, and therefore seed persistence in the soil and the volunteer oilseed rape issue, was investigat-ed. Following these objectives, several field and laboratory experiments were conducted to generate data for three published scientific papers. Paper I: A two-year field trial was conducted to evaluate the performance of the Clearfield® system in oilseed rape under different management intensities compared to a more com-monly used pre-emergence herbicide system. The Clearfield® system is an alternative weed management system for oilseed rape. It is a combination of a broad-spectrum post-emergence herbicide and a Clearfield® oilseed rape variety that has tolerance to the herbi-cide. This tolerance was implemented in Clearfield® oilseed rape varieties through conven-tional, non-GM breeding techniques. Clearfield® herbicides have lethal effects on non-Clearfield® oilseed rape varieties. Paper II: An investigation was made through laboratory and field trials on the effect of ger-mination-promoting substances (nutrients and gibberellic acid) on the development of sec-ondary dormancy of oilseed rape seeds and on their persistence in the soil. Paper III: In a three-year field trial, hoeing as a weed control method was compared with a commonly used herbicide strategy. The hypotheses made in the introduction were both confirmed and refuted by the findings obtained in the trials. Hypotheses stated in paper I: (i) The Clearfield® herbicide and herbicides of a common practice pre-emergence strategy show similar efficiencies; (ii) Management intensity has an effect on weed density but does not affect yield; (iii) Herbicide strategy does not affect yield. At higher management intensities, both herbicide systems achieved comparable efficien-cies. At lower management intensities, especially in terms of seeding density and tillage, weeds were less efficiently controlled with the Clearfield®-system, and yields were par-tially lower. At higher management intensities, higher yields and lower weed emergence were observed compared to lower intensities, presumably due to better weed control by plowing and more favorable emergence conditions due to a higher tillage intensity. Hypotheses stated in paper II: (i) All tested substances reduce the induction of secondary dormancy; (ii) the tested sub-stances reduce the induction of secondary dormancy to different extents; (iii) the tested substances have an effect on the induction of secondary dormancy, regardless of whether the tested oilseed rape seeds originate from varieties with a high or low tendency, to devel-op secondary dormancy; (iv) if a variety tends to develop high secondary dormancy, its in-duction is reduced to a greater extent by the tested substances than in seeds from a variety with a low tendency to develop secondary dormancy. Most of the tested substances reduced both the induction of secondary dormancy and the survivability of oilseed rape seeds. The efficiency of the reduction depended on the type of substance and the oilseed rape variety. Substances containing gibberellic acid proved most effective, followed by micronutrient treatments and potassium nitrate. Hypotheses stated in paper III: (i) Hoeing achieves the same weed control efficiency as herbicides; (ii) regardless of whether herbicides or hoeing are used as weed control, the same oilseed rape yield can be realized. Weed biomass was higher compared to herbicide application when hoeing was used as a weed control measure. This is probably due to the weather-dependent efficiency of hoe-ing and its only partial surface applicability. Weeds emerging in or close to the seed row cannot be controlled. Nevertheless, no yield differences were found between hoeing as a weed control measure and pure chemical weed control. The competitive strength of the varieties used was most likely large enough to ensure this yield stability. Both hoeing and applying the Clearfield® system under higher management intensities re-sulted in similarly high oilseed rape yields compared to conventional herbicide strategies, although weed control efficiency was lower. As long as no hard-to-control weeds occur on a conventional farm and a common herbicide strategy effectively controls existing weeds, changing the weed management system is less beneficial. Because the Clearfield® system increases selection pressure on weeds, the occurrence of weed herbicide resistance be-comes more likely. In addition, Clearfield® volunteer canola is more difficult to control chemically in subsequent crops. Hoeing efficiency is weather dependent, weeds are only captured between rows, and area performance is lower. However, when difficult-to-control weeds increasingly minimize the efficiency of existing, conventional chemical control strategies, both hoeing and the use of the Clearfield® system in combination with a common herbicide strategy can expand weed control options and in-crease their efficiencies. When applying the Clearfield® system, strategies should be em-ployed to minimize the occurrence of Clearfield® volunteer oilseed rape in subsequent crops. It has been shown in this thesis that germination-promoting compounds, particularly gib-berellic acid, prevent the induction of secondary dormancy, as well as the ability of oilseed rape seeds to persist, and therefore, have the theoretical potential to contribute to a reduc-tion in the volunteer oilseed rape occurrence problem. Overall, both hoeing and the application of the Clearfield® system as alternative weed man-agement systems can usefully complement established methods of weed control in oilseed rape, where necessary. In addition, the use of germination-promoting compounds in oilseed rape seeds has demonstrated the theoretical potential to contribute to a reduction of volun-teer oilseed rape as a weed in crop rotations.