Chemical manipulation and mechanisms of weed seed persistance, dormancy release and germination

An undeniable and expensive problem of any agricultural practice is the adaptation of weeds to these agricultural systems. This problem is further amplified by climate change, weeds adapt very quickly to environmental change including heat stress. The sustainable intensification of food production necessary to feed the world's growing population will only be achievable if crop harvest losses can be minimised. About 10% of crop production is currently lost to weeds and this loss would be far greater without the use of herbicides. However, the continued effectiveness of herbicide technology is threatened by the rapid advance of weed biotypes that are resistant to herbicides. Resistant weeds are now a problem across most chemical classes of herbicide and also across all the major cropping regions. Thus weed control represents a major concern for global food security, especially given that no new herbicide modes of action have been commercialized since the 1980s. New weed control tools are urgently required especially in the UK where EU/UK regulations have caused shrinkage in our 'crop protection toolbox' ("Healthy Harvest" initiative, UK National Farmers Union). Investment in crop protection in Europe has fallen from 33.3% of worldwide investment in the 1980s to 7.7% today. There is an urgent need for the development of new active substances which are effective and environmentally safe for the production of healthy food. This is also important for food quality and for preventing further food price rises which have recently affected UK consumers more than those in the mainland Europe.
The problem of effective weed control is most severe in annual field crop systems and with annual weeds which emerge at the same time as the crop seedlings. These problem weeds owe their success, at least in part, to the formation of large and persistent soil seed banks. The premise of the current application is that novel and effective weed control tools might be found in compounds that either 1) promote the coordinated germination of weed seeds in the soil bank and/or 2) in 'seedicides' that kill weed seeds at the ungerminated or a very early germination stage. In the former case, germination-promoting compounds might be applied prior to conventional herbicides (or alternative non-chemical strategies) to achieve more effective control of the total weed seed population while 'seedicides' might be applied after crops have emerged in order to limit late weed emergence. Currently, while some germination stimulants are known, none are commercial and neither do any commercial herbicides deliberately target seed-specific processes. All classical herbicides target processes of growing weed seedlings. Thus there is considerable potential for novel weed control solutions through engaging a deeper understanding of the processes of weed seed germination, survival and persistence.
This project establishes a collaboration between the Seed Biology Group of Prof G Leubner at Royal Holloway University of London and Weed Control Research Biology at Syngenta's International Research Centre Jealott's Hill. We plan to investigate the described issues with several representative problem weeds by first modelling their germination responses to a wide range in ambient temperatures, and then by choosing key temperatures to investigate the underlying hormonal changes and molecular mechanisms without and with the application of compounds known to break dormancy and induce germination of seeds. The obtained knowledge will be used to select compound libraries and screen for novel chemicals which have the potential to either promote the coordinated germination of weed seeds and/or to act as 'seedicides'. This will potentially identify novel modes of action instrumental for downstream research to fill our 'crop protection toolbox' with novel chemicals. Our project will generate knowledge to guide the development of novel strategies to control weeds by depleting the seed bank.

The overall aim of this project is to gain a deeper understanding of the fundamental mechanisms of chemically-manipulated persistence, dormancy release and germination of weed seeds imbibed at key temperatures under lab conditions. The objectives and deliverables of this project are achieved in a collaboration between the Seed Biology Group of Prof G Leubner at Royal Holloway University of London and Syngenta Weed Control at Jealott's Hill International Research Centre. We will conduct cross-species weed seed dormancy and germination thermal-time modelling as affected by selected known dormancy release and germination stimulant (DR/GS) chemicals. This will deliver the quantitative physiological framework for the subsequent comparative hormone and transcriptome profiling to elucidate molecular mechanisms of DR/GS chemicals for different weed species at key temperatures and times during seed imbibition. From the phylotranscriptomics we will select differentially expressed genes and derive candidates for conserved and seed-specific target mechanisms. Together with published knowledge this will serve to select target-catalogue based compound libraries by utilising computional chemistry. Using Syngenta's expertise in high-throughput screening we will screen compound libraries to provide novel DR/GS chemicals for weed seed research. Further to this, we will also conduct screens to chemically manipulate weed seed persistence to study the molecular mechanisms underlying suicidal germination and to identify specific targets affecting seed longevity, aging and death. The mechanisms of two potential 'seedicides' will be analysed on the hormonal and transcriptome (RNAseq, qRT-PCR) level in distinct weed species. Our project has the potential to identify novel modes of action and to generate knowledge to guide the development of novel strategies to control weeds by depleting the seed bank.

The UK has a highly successful agricultural industry which also exports food, but the UK is not self-sufficient in food production (www.foodsecurity.ac.uk). Therefore many domestic and international factors affect food production, prices, security and quality. This became for example evident during the 2008 world food price spike and the subsequent food price rises have affected UK consumers more than those in the mainland Europe. Furthermore, the reliance of imported food through trading is becoming increasingly unstable as a food security strategy, as we witness unforeseen destabilisation in developing markets such as Eastern Europe. Among the major threats to food production are in-crop weed competition and heat stress which cause severe harvest losses and have the highest negative impact on the sustainable intensification of food production (reports including Living with Environmental Change and The Royal Society Reaping the Benefits). Problem weeds owe their success and rapid adapation to climate change, at least in part, to the formation of large and persistent soil seed banks. This problem is further amplified by herbicide-resistant weeds (e.g. Busi et al. Evolutionary Applications 6:1218-21, 2013) which compromise classical weed management strategies and are most severe for annual weeds in annual field crop systems. A deeper understanding of germination/dormancy of weed seeds has been identified as a key area within Syngenta, specifically in relation to challenges of weed management which are a focus at Syngenta's Jealott's Hill International Research Centre. Our research will establish a collaboration of mutual benefit which will expand the expertise and research possibilities of both partners. Farmer and consumer will benefit from novel and safe herbicides for mitigating problem weeds for the production of healthy food.
Identifying new tools for weed control is especially critical for the UK as crop production levels and regulations cause shrinking of our 'crop protection toolbox' ("Healthy Harvest" initiative of the UK National Farmers Union). UK farmers therefore become less competitive against imported food produced to lower standards. The number of herbicide resistant weed species is growing in all regions of crop production, whilst the rate of introduction of new herbicidal products has declined. Indeed the last introduction of a novel mode of action was in the 1980's. The central scientific objective of our project is pre-competitive research to provide fundamentally novel and comprehensive insight into the mechanisms of chemically manipulated persistence, dormancy release and germination of weed seeds in response to distinct ambient temperatures including heat stress. Manipulation of weed seed behaviour will open up new opportunities for robust weed control strategies, without relying on the need to identify and register new herbicides. Identification of new herbicides is extremely difficult due to unique regulatory requirements in the EU which is discouraging investment in this space. Lack of new tools and deregistrations is eroding the competitiveness of UK/EU agriculture versus other major agricultural regions. New technologies to manipulate the weed population via the seed bank would be a significant supplementary approach to maintaining/increasing crop production, and extension of the weed control strategies available to UK/EU farmers. This project will also train research staff at the interface of fundamental seed biology and applied research into herbicides in weed control and thereby produce experts required for the UK job market in weed research and management. Regulators and government bodies will also benefit from evidence-based knowledge about herbicides in weed seed management. Clearly this research has impact on mitigating a major current threat for food production, and therefore enhances food quality, harvest quantity and the competitiveness of the UK bioeconomy.