Plant disease
scientists from across the nation gather in a Santa Rosa, Calif., auditorium
to hear one of their stars, University of California at Davis forest
pathologist Dave Rizzo (’83), describe an oak-killing scourge
he helped discover.
Knowing that the
audience is anxious for news on whether sudden oak death afflicts California’s
majestic redwoods or some other new host plant or tree, Rizzo, barely
concealing a mischievous grin, flashes a photo of a tomato on a screen
and announces that the juicy fruit is the latest host. Laughs follow
all around. The audience gets the point: Even a devastating disease
that has spread through coastal California and could potentially reach
the East Coast can’t possibly harm every living plant or tree.
“It would
be nice if this thing was only on oaks. Rhododendrons were a big shift.
Then we realized it was on other hosts and another continent. When we
hit bay, then we thought, oh my gosh, it can hit all sorts of families,”
says Rizzo, a former biology major who found his life’s passion
at JMU during backpacking and camping trips through woods and forests
from the Blue Ridge Mountains to the Allegheny Plateau.
For almost 20
years, much of Rizzo’s work in forest pathology has been on oak-root
fungus and wood-decay fungi in labs and forests far from the public
eye. Rizzo’s life changed two years ago, however, when he and
U.C.-Berkeley colleague Matteo Garbelotto discovered the microbe that
causes sudden oak death. The forest pathologists find themselves in
demand across the nation for conference presentations, town hall briefings
and news media interviews. Each now commands six-figure research budgets
and oversees sizable lab teams aimed at finding a way to save California’s
landmark oaks and prevent sudden oak death from spreading.
They have been
finding and announcing one new host after another, tallying a worrisome
list of 17 plants and trees. Sudden oak death has been found across
12 coastal California counties, and regulators fear it could reach into
the Sierra Nevada and even endanger East Coast forests, where two oak
species — northern red oak and pin oak — might be susceptible.
The Virginia of Rizzo’s college days is at high risk. European
scientists have found the same organism that causes sudden oak death
on rhododendrons in Germany and the Netherlands.
“It is a
national priority now,” says Paul Tooley, who leads the U.S. Department
of Agriculture’s studies into the threat sudden oak death might
present to a variety of East Coast plants and trees. Tooley’s
experiments are conducted in a former army lab at Fort Detrick, in Frederick,
Md. He credits Rizzo, Garbelotto and their assistants with learning
a lot in a relatively short time and helping Tooley’s staff to
get going on similar research. “Science moves forward with people
like Dave, who share their knowledge freely and welcome others in, getting
together with colleagues and kicking things around,” Tooley explains.
“That’s helped tremendously in advancing the science and
prioritizing research.”
Norlyn Bodkin
isn’t surprised his former biology student has excelled in the
field. He says Rizzo was enthusiastic and sharp — one of those
quick studies that stands out in class. “There are kids who you
can tell are obviously with you every step of the way. Those are the
kinds of people who keep you in the business, and now he’s doing
it,” says Bodkin, who was a biology professor and director of
the Edith J. Carrier Arboretum before retiring two years ago.
Rizzo, 40, grew
up in suburban Philadelphia and has been a research scientist and professor
at U.C. at Davis since 1995. He became one of the foremost research
scientists in his field while working at four universities in the East
and Midwest before arriving at Davis. The bookish Davis resident is
a family man who savors time with his wife and two young daughters.
In the field, he has experimented on pine and cedar diseases in Yosemite
Valley and pine and fir diseases in the Lake Tahoe basin. He dropped
a wood-decay fungi project in Yosemite to make time for sudden oak death
but has kept experiments going in the Sierra Nevada on both oak-root
fungus and the response of insects and diseases following control burns.
Rizzo was teaching
in the spring of 2000, when a USDA Forest Service scientist called him
to help with some fieldwork in Marin County, Calif. — ground zero
for sudden oak death. Garbelotto, the U.C.-Berkeley scientist, had spotted
a dark ooze on tree trunks that he suspected revealed the culprit that
had caused the disease.
Days later, Rizzo,
known for having a sharp eye for oak maladies, went into the same Marin
County woods and took the first sample after just one look at the dark
ooze — with the first whack of his axe. “Two days later
it grew out, and my life changed, that’s fair to say,” he
says. “Now I sit in front of my computer and talk to reporters
while my students are getting out into the woods.”
Rizzo grew it
in petri dishes, and Garbelotto identified its genetic code through
sophisticated lab methods. They determined that an exotic, fungus-like
organism never before seen in California causes sudden oak death. Sudden
oak death is caused by Phytophthora ramorum. It is genetically distant
from most of the other 60 species within the genus Phytophthora. The
pathogen is related to the fungus thought to have caused the Irish potato
famine in the 19th century and the fungus responsible for the modern
death of Port Orford cedar trees in the Pacific Northwest.
Sudden oak death
has killed tens of thousands of oaks, hitting coast live oak, black
oak, tan oak and Shreve oak. It also has been found to harm redwood,
Douglas fir, rhododendron, manzanita, California huckleberry, madrono,
California bay laurel, California buckeye, big leaf maple, California
coffeeberry, toyon and California honeysuckle, as well as arrowwood
in Europe.
The scientists,
with their assistants, have continued making critical discoveries about
new host trees and shrubs, how the microbe survives, spreads and attacks.
No treatment has been found to kill the disease or stem its spread,
but they remain hopeful. “I’m grateful every day that we
have them,” says Susan Frankel, the USDA Forest Service official
who first hired them to work on sudden oak death. “We were really
lucky. We were looking for the best people.”
Rizzo and Garbelotto
are technical advisers to the board of the California Oak Mortality
Task Force, which Frankel chaired during its first year. The work on
sudden oak death is possibly their greatest challenge yet. Not only
is it an exotic forest pest, but people want more answers faster than
the scientific process can yield them. “The scientists are being
asked to give answers for things that they still don’t know enough
about,” Rizzo says.
Then there are the funding and lab staff levels that would make them
the envy of many university scientists. “There’s pressure
out there,” Rizzo says.
“[But] if
you get frustrated easily, you wouldn’t be in this business.”
Scientists expect to find more than the current 17 hosts; they have
found the disease also harms redwoods, a development that is a blow
to the environment as well as logging and recreation. With many California
vineyards planted in oak habitats, scientists are beginning experiments
to find out whether grapevines could be victims. “The growing
list started making us think, awhile back, we should start looking at
economically important crops in the areas where this is breaking out
to make sure it won’t cause damage,” says Steve Swain, sudden-oak-death
project coordinator for the U.C. Cooperative Extension office in Sonoma
County.
“One of the scary things about plant diseases is they aren’t
always host-specific and can be fairly adaptable,” Rizzo says.
Observations in Sonoma County have turned up infected bay laurels in
a far more widespread area than oaks. Scientists suspect the disease
moves from place to place on bay laurel leaves and then kills oaks along
the way.
Another concern
is the role El Niño-spawned winter storms might play in spreading
sudden oak death. Rizzo says the microbe that causes the disease moves
into areas during cool, wet months. So it could take off during El Niño
periods, when rainfall is greater and lasts longer. Scientists also
suspect it spreads through the air, by rain splash and by humans.
While its spread
is daunting, sudden oak death faces tough foes in Rizzo and Garbelotto.
Swain figures he knows something about diseased trees, but is often
amazed at how the pair consistently gets good results quickly.
“Water-stained
bark, that’s not much to go on,” he notes. “A lot
of this is intuitive, seat-of-the-pants stuff.”
Rizzo is a wizard
in the woods. He has designed experiments to learn that the fungus-like
organism survives in rainwater, soil and leaf litter.
Garbelotto is
a genius in the lab. He has developed techniques to read the micro-organism’s
genetic code quickly and with near perfection. He has designed probes
to get its DNA out of wood and bark ooze. “I’ve worked in
collaborations a lot, and it’s like you’re always guarding
a little bit. We’ve never had any reservations. We completely
trust each other,” Garbelotto says. “He’s an extremely
knowledgeable person, and he’s very humble about it. When he talks
I really listen to him,” he says.
This is the first
disease Rizzo can remember knowing nothing about in the beginning, so
he welcomes Garbelotto’s expertise. “I don’t think
we could have gotten this far along this quickly. We can divide up a
large workload to answer a lot of questions. We still have the problem
of learning what we’re dealing with,” Rizzo says.
In presenting
findings, Rizzo often does the writing and Garbelotto the talking. “I
think I’m a lot more boring than him,” Rizzo says. “But
we both love to go out into the woods.”
Growing up in
the suburbs of Philadelphia, Rizzo spent hours walking through woods
and fishing along streams. “I used to spend all day out in the
woods, collecting frogs, collecting snakes, that kind of stuff —
not fungi. I didn’t start getting into those until college,”
he recalls. Rizzo didn’t travel much in his youth, and the Shenandoah
Valley was an exotic eye opener when he visited JMU. “It is surrounded
by mountains and forests on both sides. Hiking, backpacking and taking
class field trips in these areas led to an interest in forests and forest
ecology,” Rizzo recalls. “Seeing different diseases in the
field was just an extension of an interest in the forests,” he
says. Bodkin’s biology class hikes into Virginia’s woods
and forests were particularly revealing, Rizzo says.
“There’s
more to biology than in a test tube,” Bodkin says. “I didn’t
believe in dragging stuff into the lab. We were out in the field a lot.
Some students look and don’t see. Not Dave,” Bodkin recalls.
A shrublike growth
that Rizzo noticed on those journeys was all that remained of what once
had been North America’s largest hardwood tree. Rizzo was eager
to learn about the demise of that American chestnut, a sturdy tree that
could reach 10 to 12 feet in diameter. Chestnut blight had decimated
the tree across the East. Trees were cut down in an effort to check
the spread of the disease.
What captured Rizzo’s
curiosity were the sprouting stumps. “I thought that was interesting
that a disease could wipe out a whole forest,” he recalls. “Little
did I know that I would be working on a disease that might do the same
thing.”
Story by Michael Coit
Photos by Gary Krueger
