- Press release
, François-Xavier Branthôme
Over the past few weeks, several publications (see the related documents at the end of this article) have confirmed the development and imminent arrival on the market of decisive solutions in the fight against the Tomato brown rugose fruit virus (ToBRFV) in which the tomato processing sector has been involved alongside other sectors that are also affected.
Most recently, TomatoNews reported on the collaboration between NRGene and Philoseed, which will lead to the availability during 2021 of varieties that are resistant to the ToBRFV. Previously, we announced the discovery by the Enza Zaden company of a gene with high resistance to the same tobamovirus, to which we return in the second part of this article in order to describe the context and prospects of this recent innovation.
Research is also progressing in other areas, particularly with regard to techniques likely to provide plants with the resistance they initially lack. This is the subject of work carried out by an Israeli research team from the Ramat Negev Desert Agro-Research Center on the advantages of grafting techniques.
Grafting with more resistant rootstocks tool in fighting ToBRFV
Israeli researchers from leading agricultural institutes have found a new way to combat a viral disease that has devastated tomato crops around the globe.
First observed in southern Israel in 2014, tomato brown rugose fruit virus, also known as TBRFV or ToBRFV, has caused untold damage to tomato plants in recent years and has been detected in Europe, North America and throughout the Middle East.
While it does not affect human health, TBRFV causes plants to grow tall and spindly, and to produce yields of roughly 30% less than before contamination. The virus also has other symptoms, including yellowing leaves, yellow spots on infected fruit or brown wrinkled patches on fruit surfaces.
Similarly to HIV in humans, TBRFV weakens the immune system of tomato plants, making them particularly susceptible to various pathogens such as fusarium solani, a group of fungi that wreak havoc on crops.
In fact, in 2015 nearly 50% of tomato crops in southern Israel were wiped out as a result of the fungi attacking plants already weakened by TBRFV.
Dr. Yuval Kaye is director of vegetable research at the Ramat Negev Desert Agro-Research Center. Together with a team of scientists from other research centers around the country, he managed to find a rootstock – the base root portion of a grafted tomato plant – that can resist the fungi.
“Thanks to the experiments that we did in the past two to three years, we found rootstocks that were more resistant or less affected by the fungi;
Tomato grafting is a horticulture technique in which a scion – the top portion of plant that produces fruit – is grafted onto a rootstock that has been selected for its ability to resist certain pathogens in the soil.”
According to Kaye, while the research on fungi-resistant rootstocks has not yet been released to the general public, Israeli farmers have already been made aware of the scientific findings.
“We’re writing our reports and we’ve passed it to the farmers, [who are] already using this knowledge to grow their tomatoes in a better way,” he said.
Kaye spoke to The Media Line ahead of the world’s largest annual conference on desertification, led by the Jacob Blaustein Institutes for Desert Research (BIDR) at Ben-Gurion University of the Negev. Titled “Feeding the Drylands: Challenges in a Changing Environment,” the virtual event took place November 16-18 and included presentations from more than 100 researchers, government officials and activists.
Kaye and colleagues from other research centers around Israel hope to present their findings on ToBRFV and fusarium solani in a scientific journal in the coming weeks. Nevertheless, he stresses that the fungi-resistant rootstocks are already available in most places around the world.
“It’s the whole research and development station here in Ramat Negev, researchers from the Arava, Volcani Center and many other people that are helping us. It’s a big initiative”, he said.
This development is music to the ears of Eran Guy, an Israeli farmer who grows tomatoes and pumpkins, among other crops. His 2015 tomato crop was devastated by the combination of TBRFV and fusarium solani. “In the beginning, the virus was a total shock. [Then] our yield dropped drastically year after year,” Guy explained. “This virus causes the plants to become very weak, which leads to other issues,” he continued. “Our crops were attacked by blights we had no idea existed. There were periods where suddenly the entire crop would be destroyed and simply collapse.”
Once inside a greenhouse, TBRFV spreads like wildfire and can contaminate all nearby plants within weeks. According to scientists, it spreads mainly via bees that collect pollen from infected plants and transmit the virus when they visit the flowers of healthy plants. The disease is especially virulent in warmer climates.
For this reason, Kaye says that researchers are now focusing their efforts on finding new ways to treat the virus itself, rather than just the fungi, in order to restore tomatoes to their initial normal state. “When we find the solution to the virus, the yield will go up by at least 30%,” he stressed.
In the meantime, with the help of Kaye’s research, Israeli farmers have gone from losing half of their crops in 2015 to just 10% last year. “We’ve reached a breakthrough and we now understand which rootstock to use and how to properly take care of the plants,” Guy explained.
“We can eradicate ToBRFV from the tomato industry with our newly found resistance”
Researchers of Enza Zaden recently announced they discovered a gene with high levels of resistance against ToBRFV, the virus that has threatened the global value chain of tomatoes. In early November, they shared more information on the resistance that will be introgressed in many more tomato varieties in the upcoming period.
It has been six years since a new virus popped up in the international tomato industry. ToBRFV was first discovered in Israel and spread rapidly into the Middle East. By now, growers all over the world have to deal with the effects of the Tomato Brown Rugose Fruit Virus. If it’s not by infection, resulting in lower yields, damaged fruits, complete loss of yields, soils that have been contaminated and became useless for tomato growing, than it is by the extensive hygiene measures and strict import rules put into place to protect countries and companies from infection.
Shortly after the discovery of the virus it was also found out that ToBRFV is a tobamo-virus, meaning that it’s very stable and can survive for a long time. “Many years even, in the soil,” Sergio de la Fuente van Bentem, plant pathology researcher at Enza Zaden, says, adding that also the viral particles of the virus are almost impossible to kill. “Only the best disinfectants can, but the main thing is protection – getting rid of all infected parts of your crop and destroy it thoroughly, since the virus can spread via seeds, which is how we presumed it has spread rapidly through the entire globe, but also via irrigation water, pollinators, and mechanically, with workers cutting or pruning and spreading the virus from plant to plant.” Then there’s the spread via the fruits itself and via other crops such as tobacco – a plant that also is affected by the virus.
Other Tobamo-viruses have been threatening the industry in the past as well, yet thanks to Tm-2 and Tm-2² resistances, the industry has been secured of a virus-free harvest for almost 55 years – that is until ToBRFV kicked in and broke these resistances.
Now the researches with Enza Zaden are presenting a gene that provides high resistance to the worldwide rapidly spreading virus. Following the discovery of the virus back in 2014, the team of the breeding company quickly acted and started doing research in order to find a solution. Following extensive tests in the Enza Zaden gene bank resulted in finding one number that contained some resistant plants and further testing resulted in the finding of a wild tomato plant producing small, green, hairy fruits.
“Finding the resistance is one thing, but breeding it in and learning more about it makes our work complicated and also time-consuming," Kees Konst, Crop Research Director Tomato says. Fortunately, they were also lucky, also research into the DNA of the genes showed that it was a single gene responsible for this resistance and this also turned out to be a fully dominant gene, meaning that it only needs to be in one of the two parental lines to ensure a resistance F1 hybrid. The finding of a molecular marker increased the breeding speed and the researchers have been able to introgress it into cultivated plants – something that took many years since they had to cross it with other tomato varieties while keeping the gene.
“It’s like finding a needle in a haystack, followed by hard work to get it in our lines”, Kees summarizes – but the results could be world-changing since the many experiments show that the resistance is so strong that the plants are not only free of symptoms, but also free of the virus itself, as is shown by a PCR method. Even field tests conducted in Jordan and even manual infection with the virus did not result in infected plants. “Meaning that with HR resistance, we can eradicate the virus from tomato crops.”
“The real distribution is unknown”
Before this specific gene turned up, the team found also genes with intermediate levels of resistance, which could result in a variety with an intermediate resistance (IR) against ToBRFV. “With intermediate resistance, the virus can maintain in the world and will continue to infect crops, both professional as well as the crops of small growers working with heirloom varieties that are often sensible to viruses. An intermediate resistance will delay the symptoms, but will not stop the spread. Only with the right high resistance (HR), we can eradicate the virus and forget about all the rulings we have been dealing with on the seeds and the risks on cross border controls and blockades.
"An HR resistance is the only way to get rid of this virus,” Prudencio Olivares says – something that as a sales manager he’s very aware of. “We’ve seen how ToBRFV is a serious threat for the whole tomato chain and even believe that the list of countries where ToBRFV is found, is too short and that the real distribution is unknown, since the molecular detection techniques needed to identify the virus aren’t implemented everywhere, making some countries unable to identify the virus.”
Now that the gene is discovered, the first question to ask is when. When can growers expect varieties that are HR to ToBRFV grown in their greenhouses? An exact date cannot be given, the team with Enza Zaden shares, since it’s still a time-consuming process. But the first HR hybrids are coming in. “We’ll start planning research trials with small amounts of plants and try to speed up getting them to the market but the varieties we bring, have to fulfill the market needs as well.” Following an analysis of the threats, they’re focusing on various key markets to help first: the Middle East, where it all started, the European market, because there’s much cross-border trade, and the Mexican market, since the US is also at stake there.
“But we believe the virus will spread, so for sure we won’t forget about other markets,” the researchers say, adding that the resistance that they found seems resistance to different ToBRFV isolates found all over the world and also explaining that they will come with a broad range of materials for different tomato types. “Small sized tomatoes, mini plums, beef tomatoes, plum tomatoes,” Kees sums up.
In addition and thanks to the collaboration of breeding companies via the international license platform, other breeding parties could also have access to the resistance.
Some complementary data:
A video is available at: https://www.youtube.com/watch?v=CnYUwb04xL0&feature=emb_logo
Sources: themedialine.org, hortidaily.com