Genetic mapping and stacking of bacterial wilt resistance QTLs for tomato cultivar development

Commodities

• Vegetables: tomatoes

Practices

• Crop Production: plant breeding and genetics

Tomato is one of the most widely cultivated vegetables worldwide; however, its production is affected by different foliar and soil-borne diseases. Among these, bacterial wilt (BW) caused by soil-borne pathogen Ralstonia solanacearum species complex (RS), is one of the most economically destructive disease affecting tomato production in the southern United States. Although several management strategies have been suggested, none have proven fully effective under field conditions. Therefore, developing and deploying resistant cultivars remains the most sustainable and cost-effective solution. Breeding for bacterial wilt resistance in tomato has been ongoing for decades, yet field level resistance in commercial cultivars has been inconsistent, largely due to the extensive genetic variability of the pathogen. The University of Florida tomato breeding program has mapped three novel quantitative trait loci (QTLs) on chromosomes 2, 3, and 9, in addition to known loci on chromosomes 6 and 12. Building on this work, this project will map potentially novel resistance loci using 150 recombinant inbred lines developed from tomato landrace CRA66, a resistance source that has not been previously mapped. Lines carrying different combinations of resistant QTLs will be identified using flanking and evaluated for disease incidence and severity against multiple RS isolates from the southeastern US. The objectives are to i) validate effective combinations of BW resistance loci, (ii) identify novel resistance alleles from CRA66, and (iii) validate molecular markers for marker-assisted selection. Outcomes from this project will accelerate tomato breeding efforts and contribute to improved long-term tomato production in the southern region.

To achieve the overall goal of developing commercially relevant tomato germplasm with resistance to BW, this project will pursue the following specific objectives:

1. Validate the effectiveness of different combinations of bacterial wilt resistance QTLs on chromosomes 2, 3, 6, 9, and 12 by evaluating tomato lines carrying stacked resistance loci against multiple RS isolates prevalent in the southeastern United States.
2. Identify and characterize novel bacterial wilt resistance loci from the tomato landrace CRA66, using a recombinant inbred line population, thereby broadening the genetic base of resistance available for tomato breeding.
3. Validate molecular markers linked to bacterial wilt resistance loci to facilitate efficient marker-assisted selection and accelerate the incorporation of durable resistance in elite fresh-market tomato breeding lines.