June 25, 2009, 7:29 PM CT

Long-term apple scab resistance remains elusive

There are hundreds of choices when picking a crabapple tree from the nursery, but a Purdue University expert says only a handful are resistant to a widespread fungus or other serious diseases.

After reviewing 33 years of data, Janna Beckerman, a Purdue assistant professor of botany and plant pathology, observed that only five of 287 crabapple varieties had durable resistance to a serious disease of crabapple trees. The results of her study were reported in the recent issue of the journal HortScience

Beckerman said data on crabapple trees and apple scab had only been done on a year-by-year basis until now. Looking over a prolonged period gives scientists a better idea of which trees have historically maintained or lost apple scab resistance.

"Whenever new plants are released, they are often touted as disease-resistant, but they have only been tested for a few years," Beckerman said. "That isn't enough time. From this data, you could see that varieties that did well for the first few years after planting often developed scab within 10 years".

The Venturia inaequalis fungus produces black scab-like lesions on the fruit and leaves. Crabapple trees with scab tend to defoliate, or lose all their leaves, in early summer, a condition that can weaken and eventually kill the trees......... Posted by: Erica      Read more         Source

June 25, 2009, 6:05 PM CT

How piranhas got their teeth

How did piranhas the legendary freshwater fish with the razor bite get their telltale teeth? Scientists from Argentina, the United States and Venezuela have uncovered the jawbone of a striking transitional fossil that sheds light on this question. Named Megapiranha paranensis, this previously unknown fossil fish bridges the evolutionary gap between flesh-eating piranhas and their plant-eating cousins.

Present-day piranhas have a single row of triangular teeth, like the blade on a saw, explained the researchers. But their closest relatives a group of fishes usually known as pacus have two rows of square teeth, presumably for crushing fruits and seeds. "In modern piranhas the teeth are arranged in a single file," said Wasila Dahdul, a visiting scientist at the National Evolutionary Synthesis Center in North Carolina. "But in the relatives of piranhas which tend to be herbivorous fishes the teeth are in two rows," said Dahdul.

Megapiranha shows an intermediate pattern: it's teeth are arranged in a zig-zag row. This suggests that the two rows in pacus were compressed to form a single row in piranhas. "It almost looks like the teeth are migrating from the second row into the first row," said John Lundberg, curator at the Academy of Natural Sciences in Philadelphia and a co-author of the study......... Posted by: Kelly      Read more         Source

June 23, 2009, 5:00 PM CT

Prairie dogs and plants?

Prairie dogs may seem like harmless little creatures, but they can inflict serious injury on plants simply by snacking on them. Plants cannot flee from their furry predators, so how do they avoid becoming a prairie dog's lunch?.

Dr. John Freeman and his colleagues explore the role of metal hyperaccumulation in plant defense in the June 2009 issue of the American Journal of Botany Certain plants species growing on soils with high metal content (such as arsenic, copper, selenium, and lead) accumulate large quantities of metals in their leaves and stems. The purpose of this metal hyperaccumulation is not fully known, but metal hyperaccumulation may increase a plant's ability to respond to drought, compete with other plants, or provide a defense against bacteria, viruses, and animals.

"It is interesting to think about the effect of the prairie dog, which was an amazing ecosystem engineer on a very large scale here in North America," said Dr. Freeman, Colorado State University. "From their prehistoric ancestors the ground squirrel to the modern prairie dog, these animals may have driven the evolution of selenium hyperaccumulation as an elemental defense against herbivory in a number of different plant species".

Dr. Freeman's research focused on the role of selenium hyperaccumulation in Stanleya pinnata (prince's plume), a wildflower correlation to mustard plants. Eventhough low levels of selenium are essential for a number of animals, consumption of high levels is toxic. But just because an overdose of selenium is toxic to animals does not mean that the presence of high levels in leaves deters animals from eating the plants; prairie dogs may not know to avoid S. pinnata until it is too late. Few studies have addressed this question and whether metal hyperaccumulation actually acts as a deterrent......... Posted by: Kelly      Read more         Source

June 21, 2009, 8:56 PM CT

Domestication of Capsicum annuum chile pepper

Without the process of domestication, humans would still be hunters and gatherers, and modern civilization would look very different. Fortunately, for all of us who do not relish the thought of spending our days searching for nuts and berries, early civilizations successfully cultivated a number of species of animals and plants found in their surroundings. Current studies of the domestication of various species provide a fascinating glimpse into the past.

A recent article by Dr. Seung-Chul Kim and his colleagues in the June 2009 issue of the American Journal of Botany explores the domestication of chiles. These hot peppers, found in everything from hot chocolate to salsa, have long played an important role in the diets of Mesoamerican people, possibly since as early as ~8000 B.C. Capsicum annuum is one of five domesticated species of chiles and is notable as one of the primary components, along with maize, of the diet of Mesoamerican peoples. However, little has been known regarding the original location of domestication of C. annuum, the number of times it was domesticated, and the genetic diversity present in wild relatives.

To answer these questions, Dr. Kim and his team examined DNA sequence variation and patterns at three nuclear loci in a broad selection of semiwild and domesticated individuals. Dr. Kim et al. found a large amount of diversity in individuals from the Yucatan Peninsula, making this a center of diversity for chiles and possibly a location of C. annuum domestication. Previously, the eastern part of central Mexico had been considered to be the primary center of domestication of C. annuum On the basis of patterns in the sequence data, Dr. Kim et al. hypothesize that chiles were independently domesticated several times from geographically distant wild progenitors by different prehistoric cultures in Mexico, in contrast to maize and beans which appear to have been domesticated only once......... Posted by: Erica      Read more         Source

June 21, 2009, 8:52 PM CT

Plant Communication

-"To thine own self be true" may take on a new meaning-not with people or animal behavior but with plant behavior.

Plants engage in self-recognition and can communicate danger to their "clones" or genetically identical cuttings planted nearby, says professor Richard Karban of the Department of Entomology, University of California, Davis, in groundbreaking research reported in the current edition of Ecology Letters.

Karban and fellow scientist Kaori Shiojiri of the Center for Ecological Research, Kyoto University, Japan, observed that sagebrush responded to cues of self and non-self without physical contact.

The sagebrush communicated and cooperated with other branches of themselves to avoid being eaten by grasshoppers, Karban said. Eventhough the research is in its early stages, the researchers suspect that the plants warn their own kind of impending danger by emitting volatile cues. This may involve secreting chemicals that deter herbivores or make the plant less profitable for herbivores to eat, he said.

What this research means is that plants are "capable of more sophisticated behavior than we imagined," said Karban, who researches the interactions between herbivores (plant-eating organisms) and their host plants.

"Plants are capable of responding to complex cues that involve multiple stimuli," Karban said. "Plants not only respond to reliable cues in their environments but also produce cues that communicate with other plants and with other organisms, such as pollinators, seed disperses, herbivores and enemies of those herbivores"......... Posted by: Erica      Read more         Source

June 21, 2009, 8:48 PM CT

Dino-not-so-soaring

The largest animals ever to have walked the face of the earth may not have been as big as previously thought, reveals a paper published recently in the Zoological Society of London's Journal of Zoology

Scientists have discovered that the original statistical model used to calculate dinosaur mass is flawed, suggesting dinosaurs have been oversized.

Widely cited estimates for the mass of Apatosaurus louisae, one of the largest of the dinosaurs, may be double that of its actual mass (38 tonnes vs. 18 tonnes).

"Paleontologists have for 25 years used a published statistical model to estimate body weight of giant dinosaurs and other extraordinarily large animals in extinct lineages. By re-examining data in the original reference sample, we show that the statistical model is seriously flawed and that the giant dinosaurs probably were only about half as heavy as is generally believed" says Gary Packard from Colorado State University.

The new predictions have implications for numerous theories about the biology of dinosaurs, ranging from their energy metabolism to their food requirements and to their modes of locomotion......... Posted by: Kelly      Read more         Source

June 16, 2009, 9:45 PM CT

Global sunscreen won't save corals

Emergency plans to counteract global warming by artificially shading the Earth from incoming sunlight might lower the planet's temperature a few degrees, but such "geoengineering" solutions would do little to stop the acidification of the world oceans that threatens coral reefs and other marine life, report the authors of a newly released study in the journal Geophysical Research Letters*. The culprit is atmospheric carbon dioxide, which even in a cooler globe will continue to be absorbed by seawater, creating acidic conditions.

"There would be a slight reduction in this problem, because land plants would be expected to be able to grow more vigorously in a high CO₂, but cool world," says Ken Caldeira of the Carnegie Institution's Department of Global Ecology, a co-author of the study with main author Damon Matthews of Concordia University, Canada, and Carnegie geochemist Long Cao. Land plants and soils would hold onto more carbon in this scenario, so less would find its way into the oceans. "However this expansion of the land biosphere, while it's a slight help to ocean acidification is not enough to make a big difference".

A widely-discussed proposal for countering warming with geoengineering involves injecting small, reflective particles into the upper atmosphere. This would partially block incoming sunlight before it reached the Earth's surface, lowering global temperatures just as volcanic ash from the Mount Pinatubo did following its eruption in 1991. But critics have warned that such a scheme might also alter rainfall patterns, damage the planet's ozone layer, or have other unexpected effects......... Posted by: Janet      Read more         Source

June 12, 2009, 5:16 AM CT

Zebra mussels hang on while quagga mussels take over

The zebra mussels that have wreaked ecological havoc on the Great Lakes are harder to find these days not because they are dying off, but because they are being replaced by a cousin, the quagga mussel. But zebra mussels still dominate in fast-moving streams and rivers.

Research conducted by Suzanne Peyer, a doctoral candidate in the University of Wisconsin-Madison Department of Zoology, shows that physiological differences between the two species might determine which mollusk dominates in either calm or fast-moving waters.

"Zebra mussels quite rapidly colonized rivers close to the Great Lakes right after their introduction, within a year or two," Peyer explains. "Quagga mussels were introduced in the Great Lakes around 20 years ago, but they are not yet found in the rivers or tend to be present in low numbers".

The mussels are similar in a number of ways. Their habitats overlap, and both are suspension feeders that filter water to extract their food. But the cousin species are different in a number of ways, too. Zebra mussels prefer to attach to a hard surface, while quagga mussels can live on soft bottoms, such as sand or silt. Zebra mussels also prefer warmer water temperatures and do not grow as big as quagga mussels.

Peyer's research focused on the ability of the mussels to attach to underlying material. Both species attach to rocks, sand, silt or each other by producing tiny but strong "byssal" threads, string-like strands of protein. These threads act as an adhesive that enable the mussels to attach to surfaces, regardless of how slippery the surface is. Byssal threads are the reason mussels are so difficult to remove from boats or water intake pipes......... Posted by: Kelly      Read more         Source

June 10, 2009, 9:41 PM CT

Reviving American chestnuts may mitigate climate change

A Purdue University study shows that introducing a new hybrid of the American chestnut tree would not only bring back the all-but-extinct species, but also put a dent in the amount of carbon in the Earth's atmosphere.

Douglass Jacobs, an associate professor of forestry and natural resources, observed that American chestnuts grow much faster and larger than other hardwood species, allowing them to sequester more carbon than other trees over the same period. And since American chestnut trees are more often used for high-quality hardwood products such as furniture, they hold the carbon longer than wood used for paper or other low-grade materials.

"Maintaining or increasing forest cover has been identified as an important way to slow climate change," said Jacobs, whose paper was reported in the recent issue of the journal Forest Ecology and Management "The American chestnut is an incredibly fast-growing tree. Generally the faster a tree grows, the more carbon it is able to sequester. And when these trees are harvested and processed, the carbon can be stored in the hardwood products for decades, maybe longer".

At the beginning of the last century, the chestnut blight, caused by a fungus, rapidly spread throughout the American chestnut's natural range, which extended from southern New England and New York southwest to Alabama. About 50 years ago, the species was nearly gone......... Posted by: Erica      Read more         Source

June 10, 2009, 8:56 PM CT

The Secret of a Snake's Slither

Snake locomotion may seem simple in comparison to walking or galloping. But in reality, it's no easy task to move without legs. Prior research has assumed that snakes move by pushing off of rocks and debris around them. But a study published this week in the Proceedings of the National Academy of Sciences says that it's all in their design--specifically, their scales.

Overlapping belly scales provide friction with the ground that gives snakes a preferred direction of motion, like the motion of wheels or ice skates. Like wheels and ice skates, sliding forward for snakes takes less work than sliding sideways.

In addition, snakes aren't lying completely flat against the ground as they slither. They redistribute their weight as they move, concentrating it in areas where their bodies can get the most friction with the ground and therefore maximize thrust. In this way, snake slithering is not unlike human walking--we, too, shift our weight from left to right to enable us to move.

See the video........ Posted by: Kelly      Read more         Source