Exploiting Plant Volatile Organic Compounds (VOCs) in Agriculture to Improve Sustainable Defense Strategies and Productivity of Crops

Reports analyzing the status of agriculture worldwide forewarn that a significant increase of the present agricultural production would be necessary to meet the future demand for food, as the world population is expected to rise from 7.3 to 9.7 billion by 2050. As a consequence, FAO recently projected that an increase of food production (70%) may be required and thus a third green revolution needs to be attained (FAO, 2017). Enhanced crop yields in the past 50 years were made possible by the introduction of mechanization, the progresses in genetics and the use of improved crop varieties, as well as the extensive use of chemicals such as fertilizers and pesticides. However, the yield of grain crops considered the main sources of human and livestock calories (e.g., rice) have already reached a “plateau” (Grassini et al., 2013). Natural resources providing fertilizers (especially phosphate, Peñuelas et al., 2013) are also depleting, and the use of chemicals has caused serious problems with food safety and environmental pollution (Conley et al., 2009). Moreover, climate change is forecasted to increase the severity and frequency of drought events (IPCC, 2014) that will cause both a reduction in plant primary production (Zhao and Running, 2009) and a future progressive exposure of agricultural soils to degradation and loss of fertility (Köberl et al., 2011). Climate change will also favor the spreading of plant pathogens into larger geographical areas where new hosts may be found (Baker et al., 2000), leading to more frequent epidemics (Anderson et al., 2004). In this context, agriculture is called to provide solutions to increase yields while preserving natural resources and the environment.

Ways of being – James Bridle

2014 biologists recorded the sounds of cabbage white caterpillars feeding on a crock cress (the most popular plant for biological experiments) – the plant ultimately released a defensive chemical when played only the sound of the caterpillars approaching (and didn’t release it when played the sound of other insects or wind)

• beautiful illustration of the kind of decentring of ourselves and of human experience at which we must become adept in oder to live better and more responsibly in a more-than-human world.
• The acknowledgment of multiple other worlds, the worlds of others, is ket to disentangling ourselves from our greatest social and technological deception, and re-entangling ourselves with a more meaningful and compassionate cosmology.

How plants secretly talk to each other

https://www.wired.com/2013/12/secret-language-of-plants/

It’s now well established that when bugs chew leaves, plants respond by releasing volatile organic compounds into the air. By Karban’s last count, 40 out of 48 studies of plant communication confirm that other plants detect these airborne signals and ramp up their production of chemical weapons or other defense mechanisms in response. “The evidence that plants release volatiles when damaged by herbivores is as sure as something in science can be,” said Martin Heil, an ecologist at the Mexican research institute Cinvestav Irapuato. “The evidence that plants can somehow perceive these volatiles and respond with a defense response is also very good.”

Most studies have taken place under controlled lab conditions, so one of the major open questions is to what extent plants use these signals in the wild. The answer could have big implications: Farmers might be able to adapt this chatter, tweaking food plants or agricultural practices so that crops defend themselves better against herbivores. More broadly, the possibility that plants share information raises intriguing questions about what counts as behavior and communication — and why organisms that compete with one another might also see fit to network their knowledge.

• how can I effect the degree to which plants sense their enivornment
• need to delve into the mechanisms of this sensing ability

Electric Signals
How does one leaf know it’s being eaten, and how does it tell other parts of the plant to start manufacturing defensive chemicals? To prove that electrical signals are at work, Ted Farmer’s team placed microelectrodes on the leaves and leaf stalks of Arabidopsis thaliana (a model organism, the plant physiologist’s equivalent of a lab rat) and allowed Egyptian cotton leafworms to feast away. Within seconds, voltage changes in the tissue radiated out from the site of damage toward the stem and beyond. As the waves surged outward, the defensive compound jasmonic acid accumulated, even far from the site of damage. The genes involved in transmitting the electrical signal produce channels in a membrane just inside the plant’s cell walls; the channels maintain electrical potential by regulating the passage of charged ions. These genes are evolutionary analogues to the ion-regulating receptors that animals use to relay sensory signals through the body. “They obviously come from a common ancestor, and are deeply rooted,” Farmer said. “There are lots of interesting parallels. There are far more parallels than differences.”

Not everyone was swayed by Lawton’s criticism. Among the renitent was Ted Farmer, then a postdoc in the Washington State University lab of renowned plant hormone expert Clarence Ryan. Farmer and Ryan worked with local sagebrush, which produce copious amounts of methyl jasmonate, an airborne organic chemical that Ryan thought plants were using to ward off insect herbivores. In their experiment, when damaged sagebrush leaves were put into airtight jars with potted tomato plants, the tomatoes began producing proteinase inhibitors — compounds that harm insects by disrupting their digestion. Interplant communication is real, they said in a 1990 paper: “If such signaling is widespread in nature it could have profound ecological significance.”

During the next decade, evidence grew. It turns out almost every green plant that’s been studied releases its own cocktail of volatile chemicals, and many species register and respond to these plumes. For example, the smell of cut grass — a blend of alcohols, aldehydes, ketones and esters — may be pleasant to us but to plants signals danger on the way. Heil has found that when wild-growing lima beans are exposed to volatiles from other lima bean plants being eaten by beetles, they grow faster and resist attack. Compounds released from damaged plants prime the defenses of corn seedlings, so that they later mount a more effective counterattack against beet armyworms. These signals seem to be a universal language: sagebrush induces responses in tobacco; chili peppers and lima beans respond to cucumber emissions, too.

Plants can communicate with insects as well, sending airborne messages that act as distress signals to predatory insects that kill herbivores. Maize attacked by beet armyworms releases a cloud of volatile chemicals that attracts wasps to lay eggs in the caterpillars’ bodies. The emerging picture is that plant-eating bugs, and the insects that feed on them, live in a world we can barely imagine, perfumed by clouds of chemicals rich in information. Ants, microbes, moths, even hummingbirds and tortoises (Farmer checked) all detect and react to these blasts.