Jan 5, 2021
Fight against tomato virus shows promise

When tomato brown rugose fruit virus, or ToBRFV, was first discovered in 2014 in Israel, little was known about the disease itself, and technologies for fighting the disorder were limited.

Today, even as the virus has spread to countries such as Italy, Germany and Mexico, firms in the industry are reporting successes developing new tests for the virus, as well as headway into breeding programs to combat the effect of the virus.

A new approach

New, cheaper tests could speed up phytosanitary “passports” for tomato imports and exports, according to a Dutch firm.

Prime Diagnostics, part of Wageningen Plant Research in the Netherlands, in November announced its biochemists and virologists had developed a new commercial test for the virus. Wageningen Plant Research develops, produces and markets reagents, both molecular and serological, for detection of plant pathogens, said Prime Diagnostics Manager Jose van Beckhoven.

“Up till now the presence of ToBRFV could be tested with a TaqMan assay only,” van Beckhoven said. The TaqMan assay, a molecular test based on the detection of DNA, has been acknowledged as the standard test for ToBRFV by International Safe Transit Association (ISTA) and the European and Mediterranean Plant Protection Organization (EPPO), he said. The antiserum developed by Prime Diagnostics is used in another kind of test, ELISA.

“The differences between the two tests lay in the sample preparation (simpler for ELISA), the specificity (the TaqMan will detect only ToBRFV), the possibilities to test a high number of samples in a high-throughput setting (which is already in place for ELISA in many labs) and the total costs per assay (sample preparation plus detection is more expensive for TaqMan),” van Beckhoven said. “Both tests need a laboratory and trained personnel to perform the test.”

He said the ELISA reagents that are produced from the antiserum are already available in the U.S., and “besides this, we know that Agdia Inc. will have an ELISA format for detection of ToBRFV (was set to be) available in December.”

Prime Diagnostics hopes to develop other assays with its new antiserum, or develop other tests or assays with the same antiserum – such as Luminex, or Lateral Flow Devices that can be used by untrained personnel in fields and greenhouses for immediate testing, he said.

Prime Diagnostics’ new reagent has a high reactivity to ToBRFV specifically as opposed to other tobamoviruses, such as tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV).

“Some labs want to see only if a tobamovirus is present without truly knowing which virus is. In this case, the correct diagnosis is not a big issue,” van Beckhoven said. “Other labs, however, want to know exactly which virus is present because of quarantine reasons. ToBRFV is a quarantine organism and extra measures need to be taken when the virus is present in a crop or seed lot.”

Better availability of tests can help trade, he said.

“Imports and exports are closely monitored by the phytosanitary bodies and only they can issue ‘passports’ for healthy seed lots or plant material,” van Beckhoven said. “A greater availability of tests could speed up the process for issuing these passports.”

Resistant variety launched

Syngenta Vegetable Seeds in late November announced the launch of its first ToBRFV resistant variety, available in early 2021.

“This first introduction is a beef-type (tomato) for passive greenhouse production,” Ruud Kaagman, Global Crop Unit Head for tomatoes, wrote in an email to VGN. “The introduction will be in Middle-East/Mediterranean countries. This is where the virus was first reported and where growers are facing significant production losses.”

Plans for Syngenta include rolling out the resistance in different varieties like cluster, cherry, baby plum and saladette.

“This is running at full speed so within the coming years you will see many more introductions of resistant varieties,” Kaagman said. “We will quickly introgress the resistance into the different tomato segments which certainly also cover growers in the U.S. (and) Mexico. These introgressions are currently running and we aim to introduce (them) within the coming years.”

Another goal is finding broader resistance to the virus, he said.

“It is essential that growers keep the level of hygiene even in case the varieties are resistant,” Kaagman said. “ToBRFV is mechanically transmittable meaning that it can be transferred by tools, people, fresh produce, etc., and it is very persistent. When the virus is still around there is always the risk that it mutates, risking a decrease of protection by the current genetic resistance. Syngenta is working on a multisource resistance to give much stronger and durable resistance to ToBRFV.”

Enza Zaden research team
Part of the tomato research team at Enza Zaden. From the left are Sergio de la Fuente van Bentem, plant pathology researcher; Kees Könst, crop research director

Gene for high resistance

Netherlands-based Enza Zaden, a vegetable breeding and seed production company with operations in 25 countries on Oct.1 announced the company had found a gene providing a high level of resistance to ToBRFV.

“It has been very important for us to find this resistance and also to communicate, so we can give the growers hope that there is a solution coming,” said Tomato Crop Research Director Kees Konst. “If you can find HR (high resistance), which is the highest level possible, that’s the best way to get rid of the virus and together we have to fight the virus.”

Enza Zaden is now breeding resistant tomato varieties.

“At this moment we are looking at the first hybrids in our own greenhouses,” Konst said. “We found this gene, and we have with it also (a genetic) marker that’s associated, so that makes breeding in a broad range of types of tomatoes relatively more easy.”

He said the company is going to work with growers to make clear choices so seed production can be increased as soon as possible. A commercial release won’t happen in 2021, but he believes it will happen within the coming years.

The tomato varieties would eventually include cherry, mini-plum, cocktail, TOV (tomatoes on the vine) and beefsteak tomatoes. Enza Zaden would focus on indeterminate tomatoes because greenhouse growers’ investments in their crops are higher than field growers.

“When we figured out this new virus was a tobamovirus, we put it on the highest priority,” Konst said. “So we put a lot of projects aside, and the focus turned to find resistance to this ToBRFV. … There was a whole team behind it.”

The gene for the high level of resistance was found in Enza Zaden’s library of germplasm of wild tomatoes – a huge seed collection of wild tomato relatives that are crossable with normal cultivated tomatoes.

“It’s like looking for a needle in a haystack, but we have identified a gene providing high resistance against ToBRFV,” plant pathology researcher Sergio de la Fuente van Bentem said in a release from the company.

‘Symptomless’ Romas trialed

Bayer in late September began its final large-scale pre-launch trials of Roma-type tomatoes to help growers address ToBRFV. The trials, which begin later this month in Mexico, will include two varieties of Roma-type tomato that claim intermediate resistance (IR) to ToBRFV.

Bayer roma tomatoesBayer is using two varieties of Roma tomatoes in trials to test for the presence of ToBRFV.

The type of IR Bayer has seen in these varieties is commonly referred to as the “symptomless carrier,” where, despite the presence of virus particles, the crop can show little or no symptoms of the virus in the leaf and/or fruit should the crop become infected by the virus, according to a news release from the company.

Following the trials, Bayer anticipates the products will be available for commercial sale in Mexico in 2021, to later be followed by offerings in other important markets around the world, according to the news release.

“ToBRFV can quickly devastate tomato crops, so Bayer worked to develop a product to help growers combat it,” said J.D. Rossouw, head of Bayer’s Vegetable Seeds research and development. “Bayer leveraged our global cross-functional teams and extensive research and development pipeline to offer a solution designed to ease the day-to-day challenges faced by growers. Our research continues across several tomato species with the goal of bringing further innovative resistance to growers as quickly as possible.”

Developing these varieties aligns with Bayer’s commitment to provide clean vegetable seeds from its Seminis and De Ruiter brands to growers around the world season after season, according to the news release.

BASF introduces variety

For the new season in Mexico, BASF is introducing its first tomato variety with intermediate resistance against ToBRFV. The new hybrid is a cherry plum tomato variety and combines intermediate resistance with strong agronomic and market performance.

“The new variety has proven its performance during two test seasons at different locations in Sinaloa, Bajio, Baja California and South Mexico,” said Hiram Gutierrez Ayala, crop sales manager for Tomato Fresh. “The variety showed a reliable resistance under light and heavy virus pressure and will contribute to a more stable supply of high-quality grape tomatoes for the domestic Mexican market and the important export markets in the U.S. and Canada. Consumers will value the snack tomatoes for their attractive appearance, shelf life and sweetness.”

“ToBRFV is a contagious plant virus which easily spreads via mechanical transmission. Infected fruits are unsellable,” said Ivan Angulo Araujo, regional product specialist Tomato Fresh. “With the intermediate ToBRFV resistance the plants and fruits will remain symptomless and sellable, offering a more reliable revenue for the growers.”

This introduction is the result of the accelerated development process for parent lines using innovative breeding practices such as indoor farming and marker technology.

The company intends to introduce new Roma type varieties in 2021 and to develop more ToBRFV resistant varieties for other tomato segments and regions over the next few years.

— Stephen Kloosterman, associate editor




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