Fine mapping of the late blight resistance genes derived from Solanum pimpinellifolium accession VI030462

Start date: August 01, 2018
End date: July 31, 2021

Budget: NTD 3,390,000

Late blight of tomato, caused by the heterothallic oomycete Phytophthora infestans (Mont.) de Bary, is one of the most destructive diseases of tomato, especially in cool and wet environments. Host resistance has the potential to be a key component in managing late blight of tomato and enable farmers to reduce fungicide use.

So far six late blight resistance genes/genomic regions (Ph-1, Ph-2, Ph-3, Ph-4, Ph-5-1 and Ph-5-2) have been identified from the wild relative S. pimpinellifolium. The World Vegetable Center (WorldVeg) and other tomato breeders have developed late blight-resistant lines with Ph-3 or combined with Ph-2. However, the pathogen is highly diverse and aggressive isolates such as Pi411 from Taiwan overcome resistance genes Ph-1, Ph-2, Ph-3 and Ph-4.

Fortunately, WorldVeg identified resistance to Pi411 in several accessions of tomato wild relatives S. habrochaites and S. pimpinellifolium (VI030462). Attempts to map resistance genes in S. habrochaites either failed or no major quantitative trail loci (QTLs) were detected. VI030462 is particularly interesting because it is an important source of whitefly resistance and transfer of P. infestans resistance genes from this species should be straightforward, requiring few backcrosses to incorporate resistance into elite tomato cultivars.

Preliminary mapping of late blight resistance genes in an F₂ population screened with Pi411 revealed that VI030462 harbors two highly significant QTLs, one each on chromosomes 7 and 11 and this resistance complements Ph-2 andPh-3. The proposed project will advance progress of these important results to achieve the following objectives: (1) verify, characterize, and fine-map the two QTLs identified on chromosomes 7 and 11 by designing more molecular markers at regular intervals in the targeted regions; (2) develop lines with shortened introgressions carrying late blight resistance genes.

The project will transfer new late blight resistance genes from S. pimpinellifolium into tropical tomato and combining this resistance with Ph-2 and Ph-3 offers the best chance for durable and stable late blight resistance.