L.A.P. Lotz

Opportunities for Products of New Plant Breeding Techniques

Various new plant breeding techniques (NPBT) have a similar aim, namely to produce improved crop varieties that are difficult to obtain through traditional breeding methods. Here, we review the opportunities for products created using NPBTs. We categorize products of these NPBTs into three product classes with a different degree of genetic modification. For each product class, recent examples are described to illustrate the potential for breeding new crops with improved traits. Finally, we touch upon the future applications of these methods, such as cisgenic potato genotypes in which specific combinations of Phytophthora infestans resistance genes have been stacked for use in durable cultivation, or the creation of new disease resistances by knocking out or removing S-genes using genome-editing techniques.

A Mobile Field Robot with Vision-Based Detection of Volunteer Potato Plants in a Corn Crop'

Volunteer potato is a perennial weed that is difficult to control in crop rotations. It was our objective to build a small, low-cost robot capable of detecting volunteer potato plants in a cornfield and thus demonstrate the potential for automatic control of this weed. We used an electric toy truck as the basis for our robot. We developed a fast row-recognition algorithm based on the Hough transform and implemented it using a webcam. We developed an algorithm that detects the presence of a potato plant based on a combination of size, shape, and color of the green elements in an image and implemented it using a second webcam. The robot was able to detect potatoes while navigating autonomously through experimental and commercial cornfields. In a first experiment, 319 out of 324 images were correctly classified (98.5%) as showing, or not showing, a potato plant. In a second experiment, 126 out of 141 images were correctly classified (89.4%). Detection of a potato plant resulted in an acoustic signal, but future robots may be fitted with weed control equipment, or they may use a global positioning system to map the presence of weed plants so that regular equipment can be used for control. Nomenclature: Corn, Zea mays L, Potato, Solanum tuberosum L. Additional index words: Autonomous navigation, autonomous weeding, glyphosate, machine-vision, site-specific weed control. Abbreviations: DIPlib, Delft image-processing library; DSP, digital signal processor; GPS, global positioning system; JPEG, Joint Photographic Experts Group; NiMh, nickle metal hydride; PC, personal computer.

Outcrossing and coexistence of genetically modified with (genetically) unmodified crops: a case study of the situation in the Netherlands

Abstract With the introduction of genetically modified (GM) crops the EU has demanded that individual member states enact measures to prevent inadvertent admixture — through outcrossing — of genetically modified organisms (GMOs) with products from conventional and organic farming. A literature review on out-crossing was prepared for the Coexistence Committee installed in the Netherlands in 2004. For sugar beet and potato, isolation distances do not appear to be of overriding importance, as true seeds are not part of the harvested product. The only route for admixture is through persistence of GM hybrid volunteers, and these should already be subject to strict control in good agricultural practice. Data on maize indicate that a distance larger than 25 m is needed to keep admixture below the EU labelling threshold of 0.9%, and larger than 250 m to remain below the 0.1% threshold as favoured by organic farming organizations. Oilseed rape is more complex because apart from pollen flow also persistence of volunteers in and outside arable fields, and hybridization with wild relatives play a role. At the present state of knowledge, isolation distances of 100–200 m and rotation intervals of 6–8 years might be warranted for the 0.9% threshold. It is as yet not clear whether a threshold of 0.1% is achievable in practice. The conclusions are compared with the measures recommended by the Dutch Coexistence Committee.

A robot to detect and control broad-leaved dock ( Rumex obtusifolius L.) in grassland

Broad-leaved dock is a common and troublesome grassland weed with a wide geographic distribution. In conventional farming the weed is normally controlled by using a selective herbicide, but in organic farming manual removal is the best option to control this weed. The objective of our work was to develop a robot that can navigate a pasture, detect broad-leaved dock, and remove any weeds found. A prototype robot was constructed that navigates by following a predefined path using centimeter-precision global positioning system (GPS). Broad-leaved dock is detected using a camera and image processing. Once detected, weeds are destroyed by a cutting device. Tests of aspects of the system showed that path following accuracy is adequate but could be improved through tuning of the controller or adoption of a dynamic vehicle model, that the success rate of weed detection is highest when the grass is short and when the broad-leaved dock plants are in rosette form, and that 75% of weeds removed did not grow back. An on-farm field test of the complete system resulted in detection of 124 weeds of 134 encountered (93%), while a weed removal action was performed eight times without a weed being present. Effective weed control is considered to be achieved when the center of the weeder is positioned within 0.1 m of the taproot of the weed—this occurred in 73% of the cases. We conclude that the robot is an effective instrument to detect and control broad-leaved dock under the conditions encountered on a commercial farm.

Sublethal effects of herbicides on the biomass and seed production of terrestrial non-crop plant species, influenced by environment, development stage and assessment date.

Guidelines provided by the OECD and EPPO allow the use of single-species tests performed in greenhouses to assess the risk of herbicides to non-target terrestrial plant communities in the field. The present study was undertaken to investigate the use of greenhouse data to determine effects of herbicides with a different mode of action on the biomass, seed production and emergence of field-grown plants. In addition, a single species approach was compared with a mixed species approach. Effects on the biomass of greenhouse and field-grown plants were found to be related at different effect levels, indicating that it might be possible to translate results from greenhouse studies to field situations. However, the use of single-species tests may not be valid. The response of a single plant species to sublethal herbicide dosages differed to the response of the same species grown in a mixture with other species.

Pollen-mediated gene flow in maize tested for coexistence of GM and non-GM crops in the Netherlands: effect of isolation distances between fields

Abstract In 2006 and 2007, field trials were performed to study the effects of the two isolation distances indicated by the Dutch Coexistence Committee, i.e., 25 m between GM (genetically modified) and conventional maize, and 250 m between GM and deliberately non-GM (e.g., organic) maize, on pollen-mediated gene flow (PMGF) under representative agricultural conditions in the Netherlands. Each isolation distance was tested at three different locations across the Netherlands in both years. For testing PMGF with the 25 m isolation distance, GM source fields of 100 m × 100 m (1 ha) were surrounded by four equally sized non-GM receptor fields at a distance of 25 m. For testing PGMF with the 250 m isolation distance, 1-ha GM source fields were surrounded by four 50 m × 50 m (0.25 ha) receptor fields in four different directions at 250 m. For the GM source field, the maize variety DKC3421YG containing the MON810 event was used with both distances. A maize variety near-isogenic to the GM variety was grown in the receptor fields to obtain good flowering synchronicity between GM and non-GM maize and thus optimal conditions for PGMF. Levels of the transgene in grain samples from the receptor fields were measured by a validated real-time PCR (polymerase chain reaction) quantification method for the MON810 event. Analyses showed the following levels of grain admixture as a consequence of PMGF, averaged over 12 fields for each isolation distance tested: at 25 m 0.084% (individual field averages ranged from 0.009%t0 0.296%) in 2006 and 0.080% (0.002% to 0.318%) in 2007, respectively, and at 250 m 0.005% (individual field averages ranged from o to 0.040%) in 2006 and 0.007% (0 to 0.037%) in 2007, respectively. Although weather conditions clearly differed between 2006 and 2007 (a hot and dry summer in 2006 vs. a relatively wet one with about-average temperatures in 2007), outcrossing rates did not differ significantly between these years.

New traits in crops produced by genome editing techniques based on deletions

One of the most promising New Plant Breeding Techniques is genome editing (also called gene editing) with the help of a programmable site-directed nuclease (SDN). In this review, we focus on SDN-1, which is the generation of small deletions or insertions (indels) at a precisely defined location in the genome with zinc finger nucleases (ZFN), TALENs, or CRISPR-Cas9. The programmable nuclease is used to induce a double-strand break in the DNA, while the repair is left to the plant cell itself, and mistakes are introduced, while the cell is repairing the double-strand break using the relatively error-prone NHEJ pathway. From a biological point of view, it could be considered as a form of targeted mutagenesis. We first discuss improvements and new technical variants for SDN-1, in particular employing CRISPR-Cas, and subsequently explore the effectiveness of targeted deletions that eliminate the function of a gene, as an approach to generate novel traits useful for improving agricultural sustainability, including disease resistances. We compare them with examples of deletions that resulted in novel functionality as known from crop domestication and classical mutation breeding (both using radiation and chemical mutagens). Finally, we touch upon regulatory and access and benefit sharing issues regarding the plants produced.

Local dominance of exotic plants declines with residence time: a role for plant–soil feedback?

Exotic plant species have shown boom-bust patterns, first becoming invasive, but then over a longer time period declining in dominance. Exotic plant species may escape from their native enemies, but might become increasingly exposed to enemies in the new range as time since introduction increases. We investigated whether soil interactions could explain a pattern in the Netherlands where exotic plant species with a longer residence time are less dominant, by performing a plant soil feedback experiment. We found no evidence that plant-soil interactions explain this pattern.

Testing the Australian Weed Risk Assessment with different estimates for invasiveness

The Weed Risk Assessment (WRA) has become an effective tool in predicting invasiveness of exotic plant species. In studies testing the WRA, exotic plant species are usually divided into major weeds, minor weeds and non-weeds. However, these divisions are qualitative, as the categories are assigned by experts. Many studies searching for plant traits that are indicative of plant invasiveness use quantitative estimates to measure invasiveness. We compared how quantitative and qualitative estimates of invasiveness may relate to WRA scores. As quantitative estimates we used regional frequency (spread), change in regional frequency and local dominance of naturalized exotic plant species in The Netherlands. To obtain a qualitative estimate we determined if the exotic plant species occurred on a black list in neighbouring regions. We related WRA scores of the exotic plant species to these qualitative and quantitative estimates of invasiveness. Our results reveal that the WRA predicted the qualitative (black list) estimate more accurately than the quantitative (dominance and spread) ones. The black list estimate matches with the overall impact of exotic species, which is assumed to incorporate regional spread, local dominance and noxiousness. Therefore, the WRA predicts the noxiousness component, but to a lesser extent the spatial components of impact of exotic species. On the other hand, studies that use regional spread and other quantitative estimates of invasiveness tend not to include the noxiousness component of impact. We propose that our analyses may also help to further solve the recent debate on whether or not performing research on exotic species.

Growth of Crop and Weeds in Growth Chambers and Outdoors

The early growth of spring barley (Hordeum ulgare L.), Brassica rapa L. ssp. oleifera (DC.) Metzger, Stellaria media (L.) Vill. and Viola arvensis Murray in growth chambers and in shading cages outdoors at different irradiance levels was compared. Leaf area and shoot dry weight were lower outdoors than in growth chambers at similar irradiance and temperature. A simulation model with temperature and irradiance responses derived from growth-chamber experiments was used to test whether outdoor growth could be estimated properly. The correlations of the regressions between simulated and measured values of leaf area index (LAI) and shoot dry weight were high. However, with some exceptions, overestimations occurred, more for shoot dry weight than for LAI, and more for 100% daylight than for lower irradiance. The reasons for this are discussed.