When most of us consider the problems linked to chemical intervention in agriculture we commonly think of the potential for chemical residues on food and the associated assault on our immune systems. The more biologically astute might also think of the damage these chemicals have inflicted on soil life and the fact that one chemical begets another and consequently the disease control capacity of the soil foodweb is increasingly compromised. However, there is another way in which our food supply is affected by chemical agriculture and it relates to both the plant’s immune system and an unanticipated viscious cycle that is linked to both nitrogen fertilisers and rescue chemicals.
How Plants Fight the Fight
Plants have an immune system that is characterised by a number of biochemical defence tools, including phytoalexins, which are highly fungicidal. Pigments in fruit and vegetables often serve to discourage unwanted pathogens and insects and they also act as antioxidants to protect the plant from UV damage when it is exposed to sunlight 12 hours a day. It is a wonderful gift from nature that these plant antioxidants also serve as protective antioxidants in humans. The more intense the colour of the fruit or vegetable, the higher the antioxidant content and, as all antioxidants work in different ways, it is a great wellness strategy to make your plate look like a rainbow whenever possible.
Flavonoids are one of the biochemicals found in pigments in the skin of fruit and vegetables. Flavonoids deter pathogens and also serve as powerful antioxidants. Resveratrol, found in grape skins is one such flavonoid and it is the powerful heart protector that supposedly accounts for “The French Paradox”. The French have the lowest rate of heart disease in Europe and yet thier diet is drenched in saturated fat including cream and butter. Their saving grace is the ubiquitous consumption of moderate amounts of red wine which is rich in resveratrol. Other biochemicals that plants can be induced to synthesise include jasmonates which are both fungicidal and unpalatable to insects. Plants can also be stimulated to produce polymer lignans to strengthen cell walls and tannins for UV screening.
Plants have two distinctly different active defence systems involving Systemic Activated Resistance (SAR) and Induced Systemic Resistance (ISR). SAR is induced by pathogen infection and often involves salicylic acid as a signalling molecule. There is increasing evidence that this natural acid can be applied to the plant to trigger an immune response. Aloe vera is well suited to this purpose as it is a very rich source of salicylic acid. Aloe vera is renowned for pain relief from sunburn and insect bites simply because salicylic acid is what aspirin is based upon.
ISR involves a different scenario, where the resistance is induced by non-pathogenic organisms or biochemical stimuli. This essentially involves tricking the plant into responding as though it were under attack. This is similar to the way that antibodies are produced in the human body in response to a vaccine. ISR can be induced using kelp, as the cytokinin component has been shown to be a trigger.
A wide variety of soil microorganisms are also capable of eliciting ISR response,s so the message here is to promote soil life diversity. The greater the number and diversity of soil microbes the greater the disease resistance. Building diversity is best achieved with regular introduction of compost teas accompanied by biostimulating food sources like kelp, fish or humates. Specialist resistance-inducing micro-organisms can also be used. These include commercially available species like Bacillus subtilis, which can fuel a flood of biochemicals from the plant that can also serve to stimulate plant growth. In fact, this bacterial species is part of a group of microbes known as plant growth promoting rhizobacter (PGPR).
There is a multi-function fungi species with a similar versatility. Trichoderma harzianum has also been shown to enhance resistance in some plants while simultaneously promoting growth. This remarkable creature is also a veracious cellulose digester (carbon builder) and it is a predatory fungi which preys upon a wide variety of soil pathogens including fusarium, phytopthera and rhizoctonia. There are very few species that offer a power package of this nature and consequently inoculums containing this organism can be invaluable additions to any program.
SAR as a Quality Inducer
There is a strong argument for allowing the plant to fight its own battles, whenever possible, as many flavour enhancers and protective phytonutrients are a byproduct of the plant’s natural defence system. If we are to reclaim the forgotten flavours, it won’t be through intensive fungicide and pesticide programs as this man-made protection actually discourages the production of these compounds.
A perfect example of this phenomenon is seen in the production of dessert wines. A botrytis cineria spore lands on a grape vine. The fungus inadvertently releases it’s signature protein. Foliar receptors in the plant detect and bind to this protein setting off a cascade of biochemical responses that trigger the expression of hundreds of genes. A flavonoid called stilbene is synthesised. Stilbene acts by blocking the enzyme released by the botrytis fungus that destroys the cell wall of the plant. Stilbenes are also responsible for the rich flavour of dessert wines made using this so-called noble fungus.
Trophobiosis – Another Coffin Nail for Chemical Intervention
Farm chemicals can be counterproductive in that they can lead to reduced production of biochemicals used for natural protection and therefore will be increasingly needed in the absence of this natural control. The chemicals also bomb the microbe bridge, reducing nutrient uptake and the potential for biological protection. However, the French researcher, Francis Chaboussou, has also shown that fungicides, pesticides and herbicides actually negatively affect plant metabolism increasing their susceptibility to pests. Nitrogen mismanagement can have a similar impact.
Chaboussou’s theory of trophobiosis simply states that the nutritional state of the crop will affect susceptability to pests and disease. This is, of course, a central principle of the biological approach, but Chaboussou’s explanation is new. He believes that protein metabolism is the key. He has shown that protein metabolism is amongst the most sensitive of all plant processes and it can be compromised with repeated use of fungicides and pesticides.
Insects and fungi prefer to feed on plants that are oversupplied with short chain amino acids and simple sugars. Amino acids are the protein building blocks and sugars offer the energy source for this process. However, when the farm chemicals have slowed down this conversion process, the consequent build up of aminos and sugars calls in the pests. Chaboussou argues very convincingly that mites, psyllids, aphids and nematodes only became major problems after the introduction of artificial pesticides in 1945 and their arrival is no accident!
Nitrogen Mismanagement also a Player
Chaboussou believes that nitrogen mismanagement is also a major player in creating conditions to foster pest and disease pressure. Heavy applications of soluble nitrogen fertilisers increase the cellular concentration of nitrate, ammonia and amino acids faster than can be used for the synthesis of protein. Every grower has experienced the increase in pest pressure after a big application of nitrogen. The green revolution plants are a good example. These hybrids were bred for heavy nitrogen usage and have been much more susceptible to pests than their open pollinated predescessors.
Herbicides can also create the offending imbalance in protein synthesis. The obvious question here relates to the GM crops that are modified to withstand constant dousing with herbicide. Will associated metabolic imbalance increase their requirement for other farm chemicals? The early indications are that this is exactly what is happening. It’s not a conspiracy, it’s simply good business to have one product beget another. However it is not good news for an agricultural system that has become increasingly dependent on petrochemicals (particularly when those chemicals are destined to rise and rise with the arrival of peak oil).
When we utilise a chemical to control a pest, the rich suite of biological compounds that the plant would naturally have synthesised in order to protect itself will not be produced. As a result, the flavour, nutritional and medicinal qualities of the plant will be reduced. You are, in essence, restricting the full expression of the plant’s potential.
If Chaboussou is correct then the chemical solution is also magnifying the problem. There is no doubt that the problem is growing. Chaboussou shows how the massive new problems associated with unmanageable viral diseases is also linked to chemical-induced imbalance. Since 1945 we have increased chemical usage, on a world scale, every year without exception, and yet every year total pest pressure has grown. This is the definition of unsustainability and we must address this issue. Inducing systemic resistance, addressing trace mineral shortages and improving nitrogen management can all help to reduce chemicals and achieve quality without sacrificing yield.