Diversifying plant genes to boost immunity
The use of pesticides in agriculture could be reduced through the introduction of customised seeds that are more resistant to the pests most commonly found in individual areas.
The finding was made by ecologists from the University of Zurich in Switzerland, who used controlled experiments coupled with observations of natural plant populations and their pests to demonstrate how genetic variation in plant defences is maintained.
The researchers showed that populations of similar plant species produce specific defences that are effective against the pest most predominant in the local pest community. As a result, a variation in the local pest community can maintain genetic variation in plants across large geographical scales.
Ecologists Tobias Züst and Lindsay Turnbull from the University of Zurich teamed up with colleagues from California, US and the United Kingdom. Together they demonstrated the importance of variation in herbivore communities. Herbivores such as aphids are a source of concern: they can damage plants and as a consequence substantially reduce yields in agricultural settings. According to the research, however, they can also play a significant role in maintaining genetic diversity.
The researchers used as their 'test plant' Arabidopsis thaliana, also known as wall cress. According to Mr Züst, the work is one of the first experimental confirmations of a theory that has been around for 40 years, namely that herbivorous insects exert strong selective pressure on their host plants. The researchers also noted that plants were quick to abandon defence mechanisms when pests were absent, confirming the high costs of these defences.
The wall cress, as with many other plants, defends itself against pests with a sophisticated chemical arsenal of its own making. The pests in turn create their own mechanisms, and over the generations evolve new mechanisms that enable them to tolerate or metabolise particular chemical components. What this means is that depending on the predominance of different pest species, different compounds will provide optimal protection, and thus the plant produces a carefully tailored cocktail that will be effective against the most likely attackers. Therefore, the researchers' first step was to study the distribution of different chemical defences in natural populations of Arabidopsis thaliana across Europe, and compare it to the geographic distribution of two important pest species: the cabbage and the mustard aphid.
'There is natural variation in chemical defences which is under genetic control', explains Mr Züst, 'and this variation is maintained by geographic variation in the composition of aphid communities. Genetic variation is the raw material for evolution', he continues, 'so the maintenance of genetic diversity is essential if populations are to respond to future environmental changes such as climate change or environmental degradation.'
In the control populations with no aphid feeding, some of the successful genotypes from aphid populations were lost. According to Dr Turnbull, this occurred because defence mechanisms are costly for the plant and often come at the expense of growth: 'Genetic diversity was only maintained across the different treatments; within each treatment much of the diversity was lost. In the control populations, this meant the loss of defended genotypes, as here investment in costly defences brings no benefit to the plant.'
Today, the genetic diversity of many plant species is being eroded. For example, agricultural plants are selected for rapid growth and maximum yield at the expense of natural defences, making the use of pesticides inevitable. In future, the findings could be used to develop customised seeds that are more resistant to specific local pest communities, thus limiting the use of pesticides.
Data Source Provider: University of Zurich
Document Reference: Based on information from the University of Zurich
Subject Index: Agricultural biotechnology ; Agriculture; Food