Herbicides and Plant Physiology. Andrew H. Cobb

substantially in agriculture to achieve the yield increases necessary to feed the world. Greater meat consumption and an expanding human population implies that crop productivity needs to double by 2050.

      5 Sustainability. One widely used definition of sustainability is ‘meeting the needs of the present without compromising the ability of future generations to meet their own needs’ (DEFRA, UK). Another considers that ‘a sustainable agriculture is ecologically sound, economically viable and socially just and humane’ (Alliance for Sustainability, www.afors.org). How can humankind tackle climate change, reduce population growth, cut out waste, educate consumers in the developed world to eat less, conserve freshwater and eat more plant products and fewer animals? Political awareness, more education and an alert and informed media may provide the answer. Indeed, Ehrlich and Harte (2015) ‘urge policymakers around the world to move the issue of food security to the top of the political agenda’. And they conclude that ‘anything less is a recipe for disaster’.

      6 Can organic agriculture feed the world? Regarding crop production, organic practices infer that the use of inorganic crop nutrition products is not allowed, genetically modified crop cultivars are not permitted and the use of chemical plant protection products for the control of pests, weeds and diseases is forbidden. Such practices are becoming widely accepted in the developed world, as they are seen as a more ‘natural’ means of crop production. Those that espouse organic farming practices often say that it is better for the environment, since it requires fewer inputs, but it is generally agreed that organic farming is less productive per hectare than conventional, intensive agriculture. More land would be needed for equivalent yields, and conversion to organic practice would release more organic carbon into the environment. Furthermore, it is doubtful that legume cover crops could replace the nitrogen fertiliser needed to give higher yields (Connor, 2008). Perhaps in the future, nitrogen fixation from the atmosphere will be possible using genetically engineered crop plants?The EU Farm to Fork Strategy, launched on 20 May 2020, has ‘aspirational targets’ for 2030 for a 50% cut in pesticide use and a commitment to dedicating 25% of agricultural land to organic farming. One wonders if the consequences of reduced yields and higher prices, to name but two, have been thought through. Furthermore, the aspiration to replace pesticides with ‘biocontrol agents’ appears idealistic. Although regularly promoted, an agreed definition of biocontrol remains elusive and, at the present time, commercial agents are expensive, are unproven in the field and no viable weed biocontrol methodology exists. At a time of imminent global recession owing to the covid‐19 pandemic, a global scarcity of food is predicted, made worse by plagues of locusts in Africa, Arabia, Iran and Pakistan adding to pressures on food security. Can food producers realistically promote organic agriculture and cut pesticide use in such uncertain times? Instead, can we use our existing practices more effectively?

      7 Plants for the future: genetic diversity. In 2016, the Royal Botanic Gardens, Kew, UK, released a report on the state of the world’s plants. It noted that an estimated 31,000 plant species have a documented use for medicines, food and materials. There are an estimated 391,000 vascular plants known to science of which 369,000 species are flowering plants. A further 2000 new vascular species are described each year. Many are wild relatives of known crops that can be a source of genetic variation to improve our crops in the future, such as tolerance to drought or possess a unique metabolism. Some 21% of the world’s plants, however, are currently threatened with extinction, especially in declining rainforests. Humankind must preserve this genetic biodiversity in seed banks at all costs for future generations (www.stateoftheworldsplants.org). The human population derives 50% of its calorific intake from only three species, namely rice, wheat and maize. The rest is derived from only 20 species. Having so few staple crops means that we lack diversity in our diets and have an over‐reliance on the chosen few. Can conventional plant breeding produce the advances in yield needed to feed our global population? Perhaps it can, with the application and more widespread adoption of gene editing techniques developed in the last decade.

      8 Can we survive without plant protection products? Currently, global agriculture is heavily reliant on plant protection products, such as herbicides, plant growth regulators, fungicides and insecticides, to maximise crop yields. Without an equivalent process, yields would be reduced by at least 20–40%, so an increase in food prices would inevitably follow, with public unrest and food volatility. The reader is encouraged to note Oerke and Dehner (2004) and Pesticides in Perspective (n.d.) for further details.I note with concern that the EU is planning to withdraw as many as 75 active ingredients from the crop protection armoury. In addition to yield losses, this will erode farmers’ margins and reduce farm productivity across the EU, and over a million jobs are at risk of being lost. There are no current viable alternatives to the use of agrochemicals. Their judicious use should be promoted and these agents preserved if we are to feed the world and ensure future food security. In order for plant protection products to be used effectively, it is imperative to have an understanding of the biology of the target organisms and how an active ingredient works in both the plant and the environment. Thus, an understanding of weed biology, soil science and plant physiology underpins herbicide choice, use and effectiveness.

      9 Is science and technology the answer? Scientists and technologists consider that appropriate scientific and technological developments might come to the rescue of humankind. Why such optimism? The answer lies in recent research findings reported in the plant sciences literature, some examples of which are noted below. The first reports a rice cultivar that has been engineered to have fewer stomata, which has resulted in an increased tolerance to drought and water availability, giving equivalent or increased rice yields. The importance of this finding is the knowledge that 2500 litres of water are typically required to produce 1 kg of rice. The authors consider that rice plants with fewer stomata should perform better when limitations on water supply threaten food security (Caine et al., 2018).A second innovation is the use of gene editing to understand how plants are able to perceive and respond to environmental signals at the cellular level and respond by alterations in gene expression. In this way, plant scientists are able to understand how biotic and abiotic stimuli, such as responses to disease or environmental change, can alter growth, development and crop yield. This advance is largely due to the generation and testing of mutants that can be incorporated into plant breeding programmes. Examples include resistance to drought, resistance to salinity, temperature and water‐logging, insect and disease resistance, potatoes free from late blight, enhanced concentrations of omega oils and vitamins, fruit and vegetables that do not turn brown on impact, and low‐gluten wheat, to name but a few.A third example is the RIPE project – Realising Increased Photosynthetic Efficiency –for sustainable increases in crop yield (www.ripe.illinois.edu). This is a collaboration of US, Australian, Chinese, German and UK universities that began in 2012 with an aim of increasing global agricultural production. Several research strategies have been developed with successful investigations that include:relaxing mechanisms of photoprotection;by‐passing photorespiration;optimising enzyme activity in the photosynthetic carbon reduction cycle;increasing the efficiency of RuBisCo; andoptimising canopies for photosynthesis.Also of note the C4 Rice Project (www.c4rice.com) that is jointly funded by the Bill and Melinda Gates Foundation, in which researchers from seven institutions in five countries are working together to develop high‐yielding rice cultivars. Their aim is to use gene editing to introduce C4 photosynthetic machinery into rice, a C3 crop, which currently accounts for 19% of all calories consumed in the world. If successful, rice plants could be 50% more productive.

      10 Finally, the ‘Hands Free Hectare’ project in the UK, demonstrated in 2016 that it is possible to drill, tend and harvest a crop of spring barley without operators of machines or agronomists in the field. It proves that there is no technical barrier to automated field agriculture. Weed control is achieved by aerial sensors that ensure that only weed‐infested areas of a field are sprayed, rather than the whole field, thereby reducing inputs. It is assumed that unmanned automation will become an increasingly important part of agriculture in the future. Achieving precision spraying with dedicated robots fitted with associated sensors is a current engineering challenge (Ghaffarzadeh, 2017). Flavell (2016) has argued that we need to generate clear plans to increase the confidence