July-August - 32

PLANT & SOIL HEALTH
A
STRAWBERRY
THREAT
California researchers work to thwart
new fusarium wilt strain
USDA scientists are working to control a new " resistance-breaking " strain of fusarium wilt, a common cause of
strawberry crop loss and death. Photos courtesy of USDA.
BY DOUG OHLEMEIER
ASSISTANT EDITOR
U
SDA scientists are working on ways to control
fusarium wilt, one of the most common causes
of strawberry crop loss and death.
An estimated 55% to 59% of California strawberries
planted in the state since 2014 are not resistant to
fusarium wilt, according to the University of CaliforniaDavis.
The fusarium wilt pathogen is called Fusarium
oxysporum f. sp. fragariae race 1 (Fof race 1).
All fusarium wilt-resistant varieties possess the same
resistance gene, called FW1. Until this year, the gene
was effective against every known fusarium wilt strain
in California.
In late 2022, a new " resistance-breaking " strain,
Fof " race 2, " was discovered in a field of organic
strawberries planted that summer in Oxnard,
California. Whole genome sequencing indicates the
Fof race 2 strain is new to science and has never
been detected worldwide. Scientists believe the
strain recently developed there. Research on the
prevalence, origin and management of the disease is
ongoing and likely to progress rapidly over the next
year, said Peter Henry, a USDA-Agricultural Research
Service plant pathologist in Salinas, California.
32 | JULY/AUGUST 2023
Warmer temperatures favor fusarium wilt and
Macrophomina crown rot, and an abnormally cool and
wet winter and spring delayed fruit production and
development of symptoms. The reduced incidence
and severity of these diseases has made it more
challenging to identify other fields that are affected by
Fof race 2. Henry has visited or tested samples from
dozens of fields this year and expects the work to
accelerate over the next few months.
In collaboration with Driscoll's, Henry designed an
assay, a laboratory investigative procedure, that has
passed initial validation for specificity towards Fof
race 2. The scientists also designed another assay,
which speeds identification of infected samples.
Multiple California research and industry labs use the
RPA (recombinase polymerase amplification) as the
most common method for identifying the causal agent
in wilted strawberry plants.
The scientists are in the process of collecting
hundreds of RPA extracts from previous seasons
from the Cal Poly Strawberry Center diagnostics lab,
TriCal Diagnostics, Driscoll's, and USDA's collection
to test for CA Fof race 2. This will allow researchers
to search more broadly for infected strawberry fields
than they could achieve by sampling diseased fields in
a single season. By the end of the 2023 season, Henry

July-August

Table of Contents for the Digital Edition of July-August

Editor's Letter
Grower Profile: Central Florida leafy greens
GLVPN Veg Connection: Vegetable crop yields
Organic Grower
Ag Tech: Fields of drones
Plant & Soil Health: Fusarium wilt
Great Lakes EXPO News: Connecting growers through the digital market space
Farm Market & Agritourism: Agreements between growers provide additional opportunities
Ag Labor Review
Classifieds
Advertiser Index
July-August - 1
July-August - 2
July-August - 3
July-August - Editor's Letter
July-August - 5
July-August - Grower Profile: Central Florida leafy greens
July-August - 7
July-August - 8
July-August - 9
July-August - GLVPN Veg Connection: Vegetable crop yields
July-August - 11
July-August - 12
July-August - 13
July-August - 14
July-August - Organic Grower
July-August - 16
July-August - 17
July-August - 18
July-August - 19
July-August - 20
July-August - 21
July-August - 22
July-August - 23
July-August - 24
July-August - 25
July-August - 26
July-August - 27
July-August - 28
July-August - Ag Tech: Fields of drones
July-August - 30
July-August - 31
July-August - Plant & Soil Health: Fusarium wilt
July-August - 33
July-August - 34
July-August - 35
July-August - Great Lakes EXPO News: Connecting growers through the digital market space
July-August - 37
July-August - Farm Market & Agritourism: Agreements between growers provide additional opportunities
July-August - 39
July-August - Ag Labor Review
July-August - 41
July-August - Classifieds
July-August - Advertiser Index
July-August - 44
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