VIRTIGATION partners WU and VC have made key advances in identifying and introgressing ToBRFV resistance into cultivated tomato varieties.
Article by Tiziana Centofanti from the VIRTIGATION project
ToBRFV: A global threat to tomato production
The emergence of ToBRFV poses a significant threat to global tomato production. This tobamovirus exhibits a broad host range, including tomato and pepper, and can overcome existing resistance mechanisms in commercial tomato cultivars. In response to this challenge, the VIRTIGATION project seeks to identify and introgress ToBRFV resistance into cultivated tomato varieties. In our latest project deliverable, project partners Wageningen University (WU) and Volcani Center (VC) have reported their progress made in defining ToBRFV-resistant tomato germplasm. For this, WU and VC pursued two complementary approaches, which we will describe in further detail below:
Wageningen University (WU): Screening for Resistance in Wild Tomato Relatives
VIRTIGATION partner WU is focused on identifying sources of ToBRFV resistance within wild Solanum species. Their researchers developed a standardized seedling assay, involving controlled inoculation of young plants with ToBRFV, followed by phenotypic evaluation (visual symptom scoring) and virological confirmation (using rapid diagnostic tests). This screening process encompassed approximately 60 accessions representing 12 different Solanum species.
WU scientists identified two accessions of S. pennellii as exhibiting resistance to ToBRFV, displaying an absence of symptoms and no detectable virus presence. These resistant accessions are now being utilized in breeding programs to introgress the resistance into cultivated tomato (S. lycopersicum). WU researchers made crosses between the resistant S. pennellii accessions and a susceptible S. lycopersicum cultivar (‘Moneymaker’). Moreover, they are generating subsequent generations (F1 and F2), and then evaluating them to map the genetic loci responsible for resistance. Segregation analysis in the F2 population derived from one of the resistant accessions confirmed the heritability of the resistance trait. They are also planning to do backcrossing to further introgress the resistance into the cultivated background.
Volcani Center (VC): Evaluating Tomato Germplasm for Rootstock Resistance
Our partner VC investigated the potential of using resistant rootstocks to mitigate ToBRFV infection via root pathways. For this purpose, the VC team screened a collection of 142 tomato accessions, including S. pennellii and S. lycopersicum lines. VC’s screening involved ToBRFV leaf inoculations, followed by phenotypic assessment and serological detection using ELISA with ToBRFV-specific antibodies.
Further VC experiments focused on evaluating the efficacy of selected accessions as rootstocks. VC researchers subjected grafted plants, consisting of a susceptible S. lycopersicum scion (carrying the Tm-22 resistance gene) grafted onto different rootstock candidates, to root inoculation by dipping truncated roots in a ToBRFV inoculum. Following this, the VC scientists then identified three accessions as providing significant protection against root-mediated infection. However, these rootstocks did not confer resistance against foliar inoculation, highlighting the need for combined scion and rootstock resistance for comprehensive protection.
Conclusions and next steps for further research
This collaborative effort of VIRTIGATION partners WU and VC has identified promising sources of ToBRFV resistance in both wild tomato relatives and existing tomato germplasm. Especially the identified resistant S. pennellii accessions provide valuable genetic resources for breeding programs aimed at developing resistant cultivars. Furthermore, the identification of resistant rootstocks offers a potential strategy for managing soilborne ToBRFV infection. Future research will focus on fine-mapping the resistance loci, developing molecular markers for marker-assisted selection, and evaluating the performance of resistant scion/rootstock combinations under field conditions.
Read here the full deliverable “Defined ToBRFV-resistant tomato varieties” produced by VIRTIGATION partners WU and VC.
© Title image: Shutterstock
