Jan 24, 2023

INSV DEFENSE: Breakthrough against INSV with first resistant lettuce varieties

(Sponsored) 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 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.

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 dual-purpose varieties can be grown very well on 80-inch beds and are tolerant to fringe burn. 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. 

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: [email protected].

For more information, visit www.rijkzwaanusa.com/insv-defense.

1. Agri Pulse – Pathogen threats loom large as funding flows to Salinas Valley lettuce research – May 2022

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