Tomato Brown Rugose Fruit Virus (ToBRFV) continues to be one of the most disruptive viruses in tomato production worldwide. Its high mutation rate and ability to exist as a complex mix of viral isolates in infected plants (Harrison, 2002) make it difficult to maintain long-term resistance.
Recently, a new threat has emerged: a single nucleotide mutation in ToBRFV—referred to as resistance breaking (RB)-ToBRFV—has been shown to overcome single-gene resistance in some tomato cultivars (Zisi et al., 2024). This raises concerns for the durability of current resistant varieties on the market.
Vegetables by Bayer, driven by its seed brands, Seminis® and De Ruiter®, has tested four tomato varieties containing multi-gene resistant technology, and the results show protection – even against the new RB-ToBRFV isolate.
What the trials showed
Two internal Bayer trials were conducted using 20 seedlings of two current varieties and two pre-commercial varieties with resistance to ToBRFV, plus a susceptible check. The seedlings were planted in a randomized complete block design with four replications of five plants each.
Fifteen days after sowing, two separate trials were conducted to study the impact of different ToBRFV isolates on tomato plants. One trial was inoculated with the standard ToBRFV isolate (St-ToBRFV), while the other was inoculated with the resistance-breaking mutant (RB-ToBRFV). To ensure the integrity of the experiments and prevent cross-contamination, the trials were maintained in separate glasshouse compartments.
Virus symptoms were evaluated at 14 and 21 days after inoculation. The evaluation used the scale developed by Gonzáles-Concha (2023), which ranges from 1 to 9, where 1 indicates no visible symptoms and 9 represents severe symptoms.
The susceptible check (left bar on each plot of Figure 1) showed ToBRFV symptoms in both trials, confirming successful inoculation. Symptoms from St-ToBRFV were more severe than those from RB-ToBRFV (score 9 vs. 5), aligning with observations reported by Zisi et al. (2024).
The four varieties scored between 1 and 3 in both trials. These initial results indicate resistance to both the original and the mutated virus strains.
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What this means for growers
"With the risk of resistance-breaking mutations on the rise, the multi-gene resistance provides an added layer of protection", the team concludes. "While Vegetables by Bayer is confirming these results in real-world field evaluations, Seminis and De Ruiter are well-positioned to deliver durable protection against ToBRFV – helping keep your yield potential and peace of mind intact."
For more information: 
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Vegetables by Bayer
ToBRFV Knowledge Center
