December 2022 - 23

STONE FRUIT
While insects are the primary transport mode for little cherry disease, underground
root grafting can also spread infection. Photo: Tobin Northfield
Leafhoppers spread little cherry disease. Diseased trees produce small-sized off-color
and flavor cherries, making the fruit unmarketable. Photo: Abigail Clarke
reside in Washington and Oregon,
with potentially different virulence
and pathogenicity (the quality or state
of originating or producing disease),
assumptions on disease progress and
appearance cannot be based on old
literature, said Scott Harper, a WSU
Department of Plant Pathology virologist.
In a project on understanding LCD
pathogenicity, Harper is collecting
symptom development observations
and physiological data from
Washington orchards, in developing a
grower field guide.
" The problem is, we know the
pathogen that causes the disease, but
don't know what happens in the plant, "
Harper said. " It's very hard to pin down,
this came from here, as leafhoppers tend
to spread everything around. But, we
are at the point to where we are able to
track and map those pathogens and how
they are spread. "
Harper is also studying infection
progress of LCD in young trees. The
pathogen is more common in the
Yakima Valley, where it started but
has slowly spread in and around the
Wenatchee region.
" It's increasing compared to last year,
with more of them this year than last
year, " he said. " It's on its way. "
A research achievement is isolating
more colonies. The colonies identified
in 2022 don't resemble populations
identified the previous year. Researchers
are confirming, sequencing and
developing cultures for those.
" What this means for growers is
researchers such as Dr. Harper's group
can now work directly with each of
the different genotypes, " said Johnson.
" He's finding a plant or insect
host, which could mean treatment
and better ways of addressing the
pathogen more quickly. "
Because X-disease can be
transplanted via root grafting,
researchers want to better understand
how quickly young trees can become
infected. While growers use many
strategies for removing infected
trees, Ashley Thompson, an assistant
professor at Oregon State University's
Fruit Tree Extension for Wasco and
Hood River Counties, is evaluating
replanting strategies for infected
orchards.
She's examining root survival and
infection rates under replanting.
X-disease observed in newly planted
orchards isn't likely transmitted by old
roots from previously infected and
removed orchards, Thompson said.
Instead, new young trees are being
infected by leafhoppers, or are coming
" pre-infected " from nurseries, she said.
Thompson plans to collect root
sample data from trees prior to
planting, track them and use new
sampling techniques being developed
by Harper. Additionally, Harper wants
to improve tree testing reliability,
allowing scientists to collect samples
from roots for X-disease before trees
are planted.
Hosted by WTFRC and OCC, the
event also included presentations on
spotted wing drosophila, cherry pesticide
residues, sweet cherry breeding, sweet
cherry bud cold hardiness, and nutrient
management. FGN
FGN | DECEMBER 2022 | 23
BLUE RIBBON
ATTENTION
GIVEN TO EVERY ORDER
Our fields are planted with the most popular
clonal and seedling fruit tree rootstock varieties.
We grow a great selection of dwarf, semi-dwarf
and standard vigor varieties for apple, cherry,
pear, plum and more...
WillametteNurseries.com
Leafhoppers' cell membranes lack cell walls, making the insects immune to most
antibiotics. Photo: Abigail Clarke
http://www.WillametteNurseries.com
December 2022

Table of Contents for the Digital Edition of December 2022
