Plants have it tough compared to animals. They have to get food, procreate and protect themselves from enemies without being able to move about.
This leaves many plant species - particularly valuable crop varieties - at risk from highly specialised predators who have evolved methods that exploit a given plant's lifestyle.
Researchers are attempting to use this knowledge, however, to destroy pests and enhance a plant's natural ability to protect itself. "We can manipulate that knowledge to shift the balance of power in favour of the plant," says Dr Peter Jones of the department of plant science at University College, Cork.
The department, which includes 25 lecturers, postgraduates and post-doctoral students, is developing a number of environmentally friendly approaches to the protection of crops. The object is to reduce or eliminate agriculture's current dependence on chemical insecticides and fungicides, Dr Jones explains.
The research effort is directed towards understanding the highly complex chemical signalling that goes on between plant and pest. Many harmful worms or nematodes and fungi react directly with plant chemicals and may be dependent on the plant to complete their life cycles.
The group, for example, has devised a successful natural defence against the damaging potato eelworm nematode using trickery. The eelworm is a specialist attacker. It lies dormant in the ground until it senses a chemical released by potato roots, when it hatches to begin feeding on the roots.
Researchers identified a terpenoid, one of many organic chemicals given off by the potato, as the trigger chemical. This was sprayed on a trial field before the potato roots formed. Thinking that dinner had arrived, the eelworms hatched but quickly starved to death, greatly reducing the eelworm population. The use of a terpenoid hatch factor to bring about a "suicide hatch" could greatly reduce dependence on insecticides to control eelworm, Dr Jones says.
Specialist predators have evolved a very sensitive but also very specific response to plant chemicals. The Colorado beetle evolved when potatoes were wild and widely dispersed, but now its life is relatively easy. It can sense potatoes from miles away but can enjoy the massive food supply available with intensive cultivation.
Yet this specialised response to and dependence on one plant species has allowed scientists to target the well-defined chemical link between plant and pest. "Because it makes these insects so successful, it also makes them vulnerable," Dr Jones believes.
Oilseed rape plants are becoming an important source of vegetable oil but are vulnerable to fungus attack. Dr Jones's group has isolated a small organic acid from the fungus, a known toxin to oilseed rape, and is now using this to "immunise" the plant against the fungus.
When attacked by pathogens, many plants try to protect themselves through "systemic acquired resistance", Dr Jones explains. A chemical "signal" is released that moves through the plant, switching on a range of genes that give off defensive chemical substances. Oilseed rape is slow to respond in this way, which means that the fungus can get a strong hold before any defensive chemicals can be released. The team isolated the fungus "elicitor" chemical - the chemical that could provoke the defensive response - and sprayed this on the plant. As a result the plant began releasing defensive chemicals, giving it a level of protection before any real fungus could come along.
"We are applying the chemical when the plant has four leaves and the effect stays until the plant is mature," Dr Jones says. He points out, however, that they are not trading off one toxic chemical - fungicide - for another, the chemicals produced by the plant itself.
"You are applying a natural chemical as the elicitor, but the defence mechanism is also a natural chemical. It is what the plant is providing to protect itself", he says.