Archive for the ‘plant health’ Category
Smaller plants better at fighting infections
The dilemma of plants fighting infections
Scientists from Tübingen reveal an evolutionary dilemma: plants that are more resistant to disease grow more slowly and are less competitive than susceptible relatives when enemies are rare
Individuals of one and the same plant species often differ greatly in their ability to resist pathogens: While one rose succumbs to bacterial infection, its neighbour blissfully thrives. Scientists from the Max Planck Institute of Developmental Biology in Germany have tracked down an explanation for this common phenomenon. Their conclusion: disease resistance can incur high costs. Especially resistant plants of mouse ear cress (Arabidopsis thaliana) produce fewer and smaller leaves, and have a competitive disadvantage in the absence of enemies. Whether it is better to invest in disease resistance or biomass is thus very much dependent on the unpredictable circumstances a plant may find itself in. Therefore both large, but vulnerable plants co-exist in nature with small, but well-protected ones (Nature, June 3rd 2010).
In the course of evolution, plants have invented many ways to defend themselves against enemies. Some produce smelly or bad-tasting ingredients, others develop thorns or have a particular effective immune response to viruses and bacteria. If selection pressure is sufficiently high, one would thus expect only those individuals to survive that are best protected. Pathogens, in turn, should have a difficult time. Everybody knows that this is not the case. Indeed, plants vary tremendously in their ability to defend themselves, and this is true not only for different species, but also for members of the same species.
The group of Detlef Weigel at the Max Planck Institute for Developmental Biology has now tracked down a variant of the ACD6 gene, which functions as a universal weapon in the fight against predators. With it, the plants both produce much more of a chemical that is directly toxic to microbes and more signalling molecules important in immunity. These enable mouse ear cress plants to combat a wide range of enemies, from bacteria and fungi to insects such as aphids. However, not all varieties have this variant. While it occurs throughout the area where mouse ear cress grows, from North Africa to Scandinavia, and from Central Asia to Western Europe, at any given place it is found in only about 20 percent of individuals. This already suggests that this variant might also confer some disadvantages.
“We could show that this gene makes plants resistant against pathogens, but at the same time it slows down the production of leaves and limits the size of leaves, so that these plants are always smaller than those that do not have this variant,” said Detlef Weigel. “But as soon as they are being attacked, the plants with the special ACD6 variant have a leg up compared to plants with the standard version. On the down side, at places or in years where there are few enemies, they are penalized and lose out compared to the larger fellow plants.” Smaller size eventually leads to reduced number of seeds and hence to fewer progeny. The conclusion of Weigel: “Just as in human society, there is no free lunch in nature.”
Original work:
M. Todesco, S. Balasubramanian, T. T. Hu, M. B. Traw, M. Horton, P. Epple, C. Kuhns, S. Sureshkumar, C. Schwartz, C. Lanz, R. A. E. Laitinen, Y. Huang, J. Chory, V. Lipka, J. O. Borevitz, J. L. Dangl, J. Bergelson, M. Nordborg, and D. Weigel
Natural allelic variation underlying a major fitness tradeoff in Arabidopsis thaliana.
Nature, June 3rd 2010
Plant geraniums to kill off Japanese beetles
Some insect pests are very specialized—usually feasting on one crop. Many are named after that one particular crop that they ingest most—like pickleworms, melonworms, and sweetpotato weevils. Unfortunately for growers of ornamentals, soybean, maize, fruit, and vegetables, the Japanese beetle is not a picky eater. It feeds on nearly 300 plant species in almost 80 plant families.
The beetle, Popillia japonica, is by far the most destructive pest of ornamental and turf plants in the eastern United States, with more than $450 million spent each year to control it and replace damaged plants.
But there is hope, since there is one plant that the hungry little critter may want to avoid—the geranium, Pelargonium zonale. Though its lovely, colorful flowers are very attractive for all and profitable for growers, the flowers are deadly to the beetles. Within 30 minutes of consuming the petals, the beetle rolls over on its back, its legs and antennae slowly twitch, and it remains paralyzed for several hours. When paralyzed under laboratory conditions, the beetles typically recover within 24 hours, but they often die under field conditions because predators spot and devour them.
Technicians prepare geranium leaves for grinding, extracting, and filtering, while entomologist (background) separates and purifies the active phytochemicals: Click here for full photo caption.
Technicians Gerald Hammel (left) and Alane Robinson prepare geranium leaves for grinding, extracting, and filtering, while entomologist Christopher Ranger (background) separates and purifies the active phytochemicals. (D1585-4)The poisoning effect of geranium flowers on beetles is not a new discovery; it has been reported in scientific papers dating back to the 1920s. But the phenomenon has not been studied in depth—how or why it happens—until recently, when Agricultural Research Service scientists in Ohio picked up where scientists left off more than half a century ago.
Currently, Chris Ranger, an entomologist in the ARS Application Technology Research Unit in Wooster, is working on a natural, botanical formulation for controlling the beetles based on paralytic compounds isolated from geraniums. Patent rights are being pursued. Ranger is collaborating with Ajay Singh, a natural products chemist from Rutgers, The State University of New Jersey.
Plant rhododendrons to protect from bugs
Plants emit compounds to both attract and repel insects. Plants planted near rhododendrons can absorb and emit chemicals given off by rhododendrons to protect themselves from insects.
Scandinavian Scientists have discovered that a species of tree defends itself from herbivore attack by using chemicals emitted by neighbouring plants. The study, published today in New Phytologist, reveals how a species of birch tree adsorbs chemical compounds from neighbouring marsh tea plants, Rhondodendron tomentosum, in a unique ‘defence by neighbour strategy.’
The team from Finland, led by Prof. Jarmo Holopainen from the University of Eastern Finland, were conducting studies into emissions of forest and peat land plants when they discovered previously unreported compounds for mountain birch from their foliage emissions. The compounds were emitted by a species of rhododendron growing nearby.
“It is well known that many plant species start to emit chemical compounds after damage by herbivores,” said the co-author Dr. Sari Himanen, from Agrifood Research Finland. “In an earlier study we accessed the compounds emitted from mountain birch following Moth feeding damage and we found that some of the trees growing next to Rhondodendron tomentosum also emitted residual amounts of the compounds ledene, ledol and palustrol. This resulted in the idea to experimentally test whether these sticky semivolatiles could actually protect neighbouring birch trees from the attention of attacking herbivores such as feeding moths. Based on experimentation in the field, in a natural habitat and in the laboratory, we discovered that a novel, potentially also ecologically meaningful effect for neighbour-emitted foliage-adsorbed semi-volatiles might take place in a boreal environment.”
Plant emissions can have several roles, including the attraction or deterrence of herbivores. Some cause an indirect defence by attracting a herbivorous natural enemy, but it is extraordinary for one plant to benefit directly from another plant’s emissions.
Read more Plants discover the benefits of good neighbors in strategy against herbivores
