Bayer says it has developed and will release new varieties of hybrid tomatoes with multiple resistant genes against tomato brown rugose fruit virus (ToBRFV).
The new hybrid varieties with “multi-stacked resistance” include large truss, medium truss, cocktail truss and cherry plum truss, as well as pink beef and new versions of its earlier multi-stacked resistant beef tomato varieties, according to the company. Bayer says the first wave of the new varieties will be available for sale starting later this summer or early fall.
Javier Quintero, global lead for tomato R&D at Bayer’s Crop Science division, told The Packer varieties with multiple resistance genes are necessary to give greenhouse tomato growers a durable strategy against ToBRFV.
“The virus produces considerable damage in the plant and the fruit and ultimately the impact is a reduction of marketable yield,” he says. “The yield loss can be very significant, up to 50%, so it is devastating.”
To add to the difficulty, the virus spreads easily by contact, a big issue in greenhouses where plants are frequently touched during pruning and management. As an RNA virus, mutation can happen very rapidly, meaning each infected plant is an opportunity for the virus to change.
“In RNA viruses, because of the replication mechanism they have, there is a higher frequency of mutation when they replicate,” he says. “This is biologically true for any RNA virus. You just need to have enough viral load and time to have mutations.
“We knew that when [ToBRFV] eventually spread, it would mutate faster and we knew that we would need to provide a solution that was durable,” he adds.
Building a Better Tomato to Combat ToBRFV
ToBRFV was first identified in Israel in 2014 and has spread rapidly since then. The virus is seed-borne, easily transferable by touch and can be spread by pollinators and irrigation water. Related viruses can remain virulent in infected soil and on surfaces for years.
Quintero says ToBRFV became devastating for tomato cultivation in 2020, so the need for a genetic solution has been known for a while. He describes the process of developing Bayer’s new multi-stacked resistant varieties as starting with identifying and obtaining multiple ToBRFV-resistant genes, primarily from wild relatives of tomatoes. These genes were then introgressed into the lines Bayer used to produce the new commercial varieties.
“For this process we used conventional breeding, but we applied advanced breeding technologies,” he explains. “We used, for example, molecular markers and other technologies to be able to ensure that we are keeping that very high quality in the fruit and agronomic traits, but at the same time bringing that resistance.
“We needed to ensure that, not only do we have plant that is resistant, we have a plant that has excellent quality,” he adds. “That is the most important thing.”
According to the company, it ran two trials testing the resistance of the new hybrid varieties. One group was tested with the standard ToBRFV, while the other was tested against a resistance-breaking version.
“At both 14 and 21 days after inoculation, the non-resistant plants exhibited severe ToBRFV symptoms, but those with multiple resistance stacks held up against both the standard virus as well as the newly characterized mutation of ToBRFV,” the company said in a news release.
Quintero says that they wanted to develop resistant varieties that produced excellent fruit quality and agronomic traits but showed low or no symptoms and a low viral load when infected.
“The lower viral load is very important, because that will reduce the mutation rate as well,” Quintero says, adding that these new varieties demonstrate all of those goals.
“We tested several new ToBRFV-resistant hybrids, and we confirmed that they hold up against the resistance-breaking virus,” he says. “We expect growers to see similar results under similar growing conditions, which is very exciting.”
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