as the tomato industry grapples with the persistent threat of the Tomato brown rugose fruit virus (ToBRFV),Bayer is pioneering innovative strategies to safeguard crops and ensure grower profitability. Javier Quintero, Global Lead for Tomato R&D at Bayer’s crop Science division, recently discussed the company’s work on multi-stacked resistance, a elegant approach designed to overcome the virus’s rapid mutation rate.

Quintero addressed the shortcomings of first-generation resistant varieties and detailed the science underpinning gene stacking. He also shared results from recent trials, demonstrating how Bayer’s latest hybrids combine robust disease resistance with enhanced fruit quality and yield. These advancements are tailored for high-tech glasshouse markets,with potential applications of the resistance-stacking strategy in other crops.

With new product launches anticipated in 2025, Bayer’s progress signifies a leap forward in sustainable tomato production.

Multi-Stacked Resistance: A Proactive Approach

Quintero explained the motivation behind Bayer’s focus on multi-stacked resistance in tomato varieties, emphasizing the limitations of first-generation ToBRFV-resistant tomatoes. “This is a very high impact virus, and we did intensive research on plant-virus interactions,” he stated. “The first generation of tomato brown rugose fruit virus (ToBRFV) resistant varieties has been useful for immediate solutions to an urgent problem. However, internal and external studies indicated that the virus is actively mutating, and we anticipated for the virus to overcome single gene resistances.”

“We now have commercial products available with multiple resistant genes, good agronomics, and very nice consumer quality.”

To address this, bayer initiated a horizontal resistance breeding strategy, combining multiple genes to provide a more durable level of resistance against virus mutations. “We now have commercial products available with multiple resistant genes,good agronomics,and very nice consumer quality,” Quintero added.

Disrupting plant-Virus Interactions

Quintero elaborated on the mechanisms by which these multi-stacked resistance genes disrupt different stages of plant-virus interaction. Research has shown that virus multiplication is substantially slowed down in the new varieties compared to susceptible ones. “It is indeed our hypothesis that the resistant genes interfere with different steps in the replication process of the virus, and the trials have been supporting this hypothesis,” he explained.

The resistance levels of selected tomato varieties were evaluated through standardized inoculated trials in heated glasshouse conditions. Plants were inoculated with a ToBRFV suspension 40 days after sowing, with infection confirmed two weeks later. Symptoms on leaves and fruits were assessed from 25 to 140 days post-inoculation using a standardized rating scale. All trials were conducted in quarantined facilities capable of testing approximately 1,000 varieties annually.

In a separate study,the performance of four new varieties was tested against a resistance-breaking strain of ToBRFV. Plants were inoculated 15 days after sowing in two parallel trials, one using the standard ToBRFV isolate (St-ToBRFV) and the other using the resistance-breaking mutant strain (RB-ToBRFV). Each trial was conducted in separate glasshouse compartments.

Symptom severity was rated at 14 and 21 days post-inoculation using the gonzáles-Concha (2023) scale, where a score of 1 indicates no visible symptoms and 9 indicates severe symptoms. The susceptible check variety, used as a control, exhibited strong symptoms in both trials, scoring 9 in the St-ToBRFV trial and 5 in the RB-ToBRFV trial, confirming effective inoculation. These results align with findings by Zisi et al. (2024). In contrast,the four Vegetable by Bayer hybrids recorded symptom scores between 1 and 3 across both trials,demonstrating strong and consistent resistance to both the original and mutated virus strains.

According to Quintero, the new hybrids perform on par or even better than previous generations in terms of yield, fruit quality, and shelf life. These hybrids exhibit durable ToBRFV resistance combined with excellent agronomic features, with no negative impacts observed due to ToBRFV resistance. Bayer has even delivered products with extra specifications, such as resistance to the fungal plant pathogen Passalora fulva.

Targeting High-Tech Glasshouse Growers

With the anticipated launch in 2025, the new varieties are well-suited for high-tech glasshouse growers worldwide. Bayer is launching products in major glasshouse market segments, including Large Truss, Medium Truss, Beef, and Cherries, deploying product launches as quickly as possible to markets in need.The main challenge is meeting the high demand for seeds while complying with local regulations.

Significant progress is also expected in Bayer’s mid-tech greenhouse program, with additional launches anticipated soon. Growers are encouraged to contact their local Bayer representatives for the latest information.

Expanding Resistance-stacking Strategies

Looking ahead, Bayer plans to apply similar resistance-stacking strategies to other crops facing threats from fast-mutating viruses. “Fast-mutating viruses are a concern across a number of crops, so we’ve established a multi-stack strategy to get and stay ahead of mutation,” Quintero stated. In addition to ToBRFV, this strategy has been successfully deployed against TYLCV and TSWV in tomatoes and is in growth across other solanum crops like peppers and cucurbit crops like cucumber, melon, and watermelon.