Location: Crop Diseases, Pests and Genetics Research
Project Number: 2034-21220-008-061-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jul 1, 2026
End Date: Jun 30, 2028
Objective:
The overall goal of this project is to build upon the knowledge already gained regarding variation in VMB resistance and extend these findings to a broader range of Vitis–Muscadinia hybrids. By expanding the scope of germplasm tested, the project will capture greater genetic diversity and provide a more comprehensive understanding of how resistance traits are expressed across different hybrid backgrounds and potentially identify genomic regions that harbor resistance. In addition, it will deepen our understanding of host responses to VMB infestation. By integrating expanded germplasm evaluation with detailed host response studies, the project will advance both fundamental knowledge of plant–insect interactions and practical solutions for sustainable vineyard management.
The specific goals are:
1. Expand the screen to ~150 VM hybrid lines to determine segregation of resistance factors, conduct genome wide association, mapping and QTL analysis of genotypic and phenotypic data.
2. Evaluate subset of resistant germplasm with two additional mealybugs (Gill’s and Citrus mealybug) to access resistance response.
3. Evaluate VMB preference on susceptible scion grafted on VMB resistant UCD-GRN1 rootstock.
4. Evaluate host response of select resistant lines to feeding of VMB via histology studies.
Approach:
This project will expand the germplasm collection to include additional Muscadinia rotundifolia lines and Vitis–Muscadinia (VM) hybrids, as these accessions have demonstrated promising resistance traits. The Department of Viticulture and Enology at the University of California, Davis currently maintains approximately 150 VM hybrid lines. Comprehensive phenotyping and genotyping of this collection will be undertaken to accelerate resistance mapping and to identify putative genomic regions in M. rotundifolia associated with resistance. These efforts will strengthen and validate findings from ongoing genome-wide association analyses. To assess the breadth of resistance, we will evaluate whether suppressive effects on mealybug growth and development extend to other mealybug species, thereby determining the consistency of resistance across vectors. Further investigation of the UCD GRN1 rootstock, along with other promising germplasm, will provide deeper insight into VMB feeding behavior and host responses. Additionally, experiments will test whether resistant rootstocks can confer protective traits to grafted, otherwise susceptible scions. This will yield critical information on the practical application of resistance in vineyard systems. Collectively, these studies will inform breeding programs, guide rootstock selection, and contribute to integrated pest management strategies that reduce reliance on chemical controls while enhancing vineyard resilience.