February 2023 - 20

INSV DEFENSE
Breakthrough against INSV with
first resistant lettuce varieties
A solution to the Impatiens necrotic spot
virus (INSV) is finally within reach for lettuce
growers. After years of intensive research and
breeding, the Dutch vegetable seed company
Rijk Zwaan is launching two Romaine lettuce
varieties for the US market with a resistance to
INSV. The varieties are the first in the company's
INSV Defense line. " We are really excited that
we can support everyone in the lettuce sector
with this breakthrough. For them, this can
make the difference between profit and loss, "
states Johan Schut and Christophe Thomas
from the Rijk Zwaan breeding team.
$100 million in lost revenue
For growers in the Salinas Valley, the USA's
key lettuce-producing area, INSV (and TSWV) -
which are transmitted by the western flower
thrips - has been a serious problem for the
past two years. A 2020 survey of 1,350 fields
revealed an average crop loss of 33% and a
100% loss in some fields, according to Mary
Zischke of the Grower-Shipper Association.
She estimates the economic impact of that
damage at over $100 million.1 Figures for 2021
and 2022 have not yet been published, but
INSV caused severe problems again - likely
well over 2020 figures.
Searching resistance against TSWV
For the Rijk Zwaan team, the INSV Defense
story began back in 2005 when they started
working to find resistance in lettuce against
the Tomato spotted wilt virus (TSWV) which
was causing problems in the south of Europe.
Johan Schut, Breeding Manager Lettuce: " We
planted numerous old, new and wild lettuce
varieties next to a pepper greenhouse. While
a lot of lettuce plants were affected, we also
found a few healthy plants. That was the start
of a classical breeding journey including the
use of advanced techniques like DNA-markers.
This journey has been a joint effort by our
colleagues in France, the Netherlands and
the US. "
TSWV resistance also effective against INSV
When INSV was first found in California
in 2012, the Rijk Zwaan team immediately
49 field trials in the past two years
Over the past two years, the US team in
Salinas and various dealers ran a total of 49
field trials, all coordinated by Ryan McMillen,
Rijk Zwaan's Lettuce Selector in the US. These
trials confirmed that two selected varieties
had high resistance (HR). " There was an
amazing difference between the susceptible
variety and our two resistant varieties: JAMMIN
RZ and FARMIN RZ, " adds Thomas.
Well adapted to US requirements
Besides the high resistance to INSV, these
two Romaine varieties also have positive
agronomical characteristics, Thomas explains:
" They both have tall hearts, a good shape
and nice yellow internal leaves. These dualpurpose
varieties can be grown very well on
80-inch beds and are tolerant to fringe burn.
ADVERTISEMENT | © 2023 Rijk Zwaan
Growers who are interested in the trial
results can contact Brandon Avilla, Lettuce
Crop Specialist, or other colleagues at the
Rijk Zwaan USA office in Salinas: contactusa@
rijkzwaan.com.
For more information visit:
www.rijkzwaanusa.com/insv-defense
1Agri Pulse - Pathogen threats loom large as funding
flows to Salinas Valley lettuce research - May 2022
realized that it could pose a problem for
lettuce, Schut says. " Because INSV is closely
related to TSWV, we conducted tests in our
lab and found that our resistance also worked
against INSV. As a result, our new varieties
have resistance to both viruses. "
When problems in the Salinas Valley
with INSV worsened in 2020, the urgency to
introduce new lettuce varieties increased.
By then, Breeder Christophe Thomas and
his team were at an advanced stage of
selecting Romaine lettuce varieties. " To
complete the process and have a real impact,
we just needed to trial them in the US, "
comments Thomas.
FARMIN RZ is slightly taller and bigger, so it
is more suitable for processing. JAMMIN RZ
is a little shorter and broader with a better
heart and therefore the best choice for the
retail market. "
More INSV-resistant lettuce varieties in
the pipeline
Pelleted seeds of both Romaine varieties
will be available in early 2023. " We are excited
to be able to support lettuce growers and
processing companies, especially in the US
market. We expect to launch INSV Defense
varieties of all lettuce types in the future, "
states Thomas.
http://www.rijkzwaanusa.com/insv-defense
February 2023

Table of Contents for the Digital Edition of February 2023
