A new publication by VIRTIGATION partner Wageningen University & Research (WUR) reports that the Tm-1 allele from Solanum pennellii accessions, together with an additional, likely recessive, locus, are required for complete ToBRFV resistance.
Background of the study
ToBRFV remains one of the most destructive plant viruses threatening tomato production worldwide. Highly contagious and able to overcome known resistance genes, ToBRFV causes severe yield losses with limited management options. Developing durable resistance is therefore a top priority for the horticultural value chain to safeguard tomato cultivation. VIRTIGATION WUR researchers offer a promising breakthrough in this regard, in a new publication in the Theoretical and Applied Genetics journal. They have identified five ToBRFV-resistant accessions of S. pennellii, a wild relative of cultivated tomato, and confirmed that the major gene controlling this resistance trait is the Tm-1 allele. More importantly, the WUR scientists also show that full ToBRFV resistance requires an additional, yet to be identified locus. Their findings highlight the potential of S. pennellii as a novel source of resistance against ToBRFV.
Tm-1: Back in Action
The VIRTIGATION WUR investigators screened ten S. pennellii accessions and found that five remained symptomless after ToBRFV inoculation. Moreover, the viral coat protein was undetectable in these symptomless plants, demonstrating strong natural resistance. They also carried out genetic analysis, which showed that plants carrying the S. pennellii version of the Tm‑1 gene in a homozygous state were resistant. When the scientists silenced Tm‑1, the plants lost resistance — proving that Tm‑1 is essential for this defense. Interestingly, the WUR researchers note in their publication that this differs from previously known Tm‑1 alleles, which are ineffective against ToBRFV.
However, not all plants with the resistant Tm‑1 allele were fully immune. The WUR study revealed that another recessive locus is required alongside Tm‑1 to achieve complete resistance to ToBRFV. While its exact location remains unknown, it represents an exciting target for future research in this field.
Future perspectives for ToBRFV resistance breeding
The WUR discovery reported in the Theoretical and Applied Genetics journal expands the toolbox available to plant breeders to develop ToBRFV-resistant tomato plants. So far, there are still no tomato plants available to growers which are fully resistant against ToBRFV. The S. pennellii Tm‑1 allele introduces a new genetic resource for ToBRFV resistance. Moreover, the WUR finding that durable resistance requires both Tm‑1 and a second locus, highlights the importance of stacking multiple genes for long‑lasting effectiveness. Furthermore, the recent WUR publication paves the way for introgression of novel resistance into tomato varieties. And while the WUR results represent a breakthrough, several challenges remain to be addressed:
- Identifying and characterising the second resistance locus
- Testing resistance stability across environments and ToBRFV isolates
- Validating performance in commercial conditions, especially in greenhouses.
By addressing these gaps, the horticultural value chain can move closer to delivering urgently needed tomato plants which are fully resistant to ToBRFV.
More info about WUR’s new publication in Theoretical and Applied Genetics
The full version of the study in Theoretical and Applied Genetics titled ‘Tm-1 back in business: an allele from Solanum pennellii accessions plays a major role in ToBRFV resistance’, authored by WUR, is available online here since 12 September 2025. WUR’s principal investigators in VIRTIGATION wrote this paper: Romanos Zois, Mireille van Damme, Martin Verbeek, Luuk D.H. Veenendaal, Yuling Bai and Anne-Marie Wolters. The datasets underlying their peer-reviewed, open access scientific publication are directly available in the publication, as well as in the supplementary information available on Zenodo. Find out more about VIRTIGATION’s scientific publications on our website here.
© Cover image: Shutterstock
