Skip to comments.FARM SCENE: Researchers Hope Hybrid Chestnuts Can Restore Species
Posted on 07/01/2002 3:34:58 AM PDT by Movemout
STATE COLLEGE, Pa. (AP) - The chestnut sapling planted on this grassy hillside doesn't look like much - just a spindly stem bearing a handful of twigs and leaves that seem entirely too big for such a small plant.
Researchers hope it is the start of a chestnut grove that will help restore a species all but eliminated from the continent over the last century.
Most of the trees are expected to eventually succumb to the blight that has killed much of the rest of their kind. But from the survivors could come the stock for eventually repopulating Eastern forests with American chestnuts.
"In this age, it would be like taking out all of the oaks, then going 100 years into the future and trying to describe an oak to people and trying to restore the oak population," said Kim C. Steiner, a professor of forest ecology and director of The Arboretum at Penn State University.
The American Chestnut Foundation and The Arboretum on June 24 planted the first saplings for the experimental chestnut grove.
Until the early 20th century, the American chestnut was one of the most abundant trees in eastern North America, often growing to 100 feet tall and more than 10 feet in diameter.
Chestnut timber was used to build homes. The wood was used for products ranging from light furniture to caskets, earning it the nickname "cradle-to-grave tree." Its warm coloring made it a popular interior wood, and the protein-rich nuts were roasted or ground into flour for baking.
In 1904, a foreign fungus called chestnut blight was introduced in New York City and quickly spread throughout the country, virtually eliminating adult chestnuts by the 1950s.
The fungus attacks only the portion of the tree that lives above ground, leaving the root structure intact. In scattered locations throughout the nation, surviving American chestnut roots send up saplings each year. Those saplings eventually are killed by the blight, but not before they collect enough sunlight to keep the roots alive for another year to sprout another sapling.
The saplings planted at The Arboretum at Penn State come from attempts to crossbreed surviving American chestnuts with Chinese chestnuts, which are not affected by the blight.
Scientists first crossed the American chestnut, a tall, straight tree well suited for timber use, with the Chinese chestnut, a shorter tree with a broader canopy resembling that of an apple tree.
The half-American, half-Chinese offspring was then bred with an American chestnut, a process repeated until the final product is 15/16ths American.
"The objective is to have a tree that a taxonomist, an expert taxonomist, would look at and think it's an American chestnut, but one that we've bred into it the blight resistance of the Chinese chestnut," Steiner said.
It's one of many projects aimed at restoring the American chestnut. In Kentucky, the American Chestnut Cooperator's Foundation planted seedlings from American chestnuts that show some resistance to the blight. Several other states, including Michigan and North Carolina, have experimental groves.
Like all forestry work, it's a long-term project. About 130 saplings were planted at Penn State, the first of more than 60,000 saplings expected over the life of the project.
Only about 1 percent of the saplings planted across the country are expected to carry the right characteristics - and even that number might be optimistic.
Researchers hope to use the best trees from Penn State and other experimental sites as breeding stock.
If successful, the blight-resistant trees could then be planted in Eastern forests again, restoring a bit of genetic diversity and once again providing a source of food and timber.
"You just plain don't know," said Herbert Darling, of Buffalo, N.Y., president of The American Chestnut Foundation. "You just have to keep shaping them, picking the very best ones, and let time tell year after year."
If they are, they aren't American chestnuts.
Mitotic stability and nuclear inheritance of integrated viral cDNA in engineered hypovirulent strains of the chestnut blight fungus.
Chen B, Choi GH, Nuss DL.
Roche Institute of Molecular Biology, Roche Research Center, Nutley, NJ 07110.
Transmissible hypovirulence is a novel form of biological control in which virulence of a fungal pathogen is attenuated by an endogenous RNA virus. The feasibility of engineering hypovirulence was recently demonstrated by transformation of the chestnut blight fungus, Cryphonectria parasitica, with a full-length cDNA copy of a hypovirulence-associated viral RNA. Engineered hypovirulent transformants were found to contain both a chromsomally integrated cDNA copy of the viral genome and a resurrected cytoplasmically replicating double-stranded RNA form. We now report stable maintenance of integrated viral cDNA through repeated rounds of asexual sporulation and passages on host plant tissue. We also demonstrate stable nuclear inheritance of the integrated viral cDNA and resurrection of the cytoplasmic viral double-stranded RNA form in progeny resulting from the mating of an engineered hypovirulent C. parasitica strain and a vegetatively incompatible virulent strain. Mitotic stability of the viral cDNA ensures highly efficient transmission of the hypovirulence phenotype through conidia. Meiotic transmission, a mode not observed for natural hypovirulent strains, introduces virus into ascospore progeny representing a spectrum of vegetative compatibility groups, thereby circumventing barriers to anastomosis-mediated transmission imposed by the fungal vegetative incompatibility system. These transmission properties significantly enhance the potential of engineered hypovirulent C. parasitica strains as effective biocontrol agents.
PMID: 8344241 [PubMed - indexed for MEDLINE]
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