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ARS Home Southeast Area Charleston, South Carolina Vegetable Research Research





- Kousik, Chandrasekar - Shaker
- Rutter, William
- 2023
- 2022
- Publications
- Plant Diseases (303)

Research Project: **Location:
                            Vegetable Research** Project Number: 6080-22000-031-000-D
                        
                        Project Type: In-House Appropriated Start Date: Apr 12, 2022
                        
                        End Date: Apr 11, 2027 **Objective:**
                        
                        1. Identify and characterize disease and nematode resistance in vegetable crops, and develop molecular tools to enhance breeding efforts for resistance.
1.A. Determine genetic basis of resistance to powdery mildew (PM) and Phytophthora fruit rot in watermelon and develop molecular markers linked to resistance genes.
1.B. Fine map quantitative trait loci (QTL) conferring resistance to watermelon vine decline (WVD) caused by Squash vein yellowing virus (SqVYV) and develop molecular markers.
1.C. Develop markers for and characterize the molecular mechanisms of resistance to root-knot nematode in cucumber.

2. Identify and develop vegetable germplasm and breeding lines with enhanced resistance to diseases and nematodes.
2.A. Identify sources of resistance to the whitefly-transmitted Cucurbit leaf crumple virus (CuLCrV) in watermelon.
2.B. Develop pepper breeding lines with pyramided nematode resistance genes.

3. Characterize population dynamics to improve biological understanding of existing and emerging fungal and nematode pathogens in the southeastern United States.
3.A. Characterize powdery mildew (Podosphaera xanthii) isolates collected from cucurbits in southeastern U.S.
3.B. Characterize the influence of temperature on the development of the guava root-knot nematode (Meloidogyne enterolobii). **Approach:**
                        
                        This approach will identify and develop resistant germplasm and breeding lines for managing Phytophthora fruit rot(PFR),powdery mildew(PM),whitefly-transmitted Squash vien yellowing virus(SqVYV), Cucurbit leaf crumple virus(CuLCrV), and root-knot nematodes(RKN). Modern reisstance phenotyping and breeding techniques will be utilized to accomplished our objectives.

A recombinant inbred line(RIL) population will be developed by crossing a multiple disease resistant watermelon line (PFR and PM) and a susceptible line. The RIL population will be phenotyped for resistance to PFR and PM to determine genetics of resistance. Analysis of differentially expressed genes by RNA-Seq resulting from Phytophthora and watermelon fruit interactions will be used to further elucidate genetics of fruit rot resistance. Red fleshed RILs with resistance to PFR and/or PM will be evaluated for fruit quality and selected for release. Similarly, a RIL population developed from a cross of SqVYV resistant watermelon line and a susceptible cultivar will be phenotyped to detremine genetics of resistance and develop molecular markers for use in breeding programs.

We will phenotype cucumber lines from a mapping population to fine map the mj resistance gene. The resulting candidate resistance genes will be cloned and characterized to provide pathologists with a better understanding of the biological underpinnings of RKN resistance and provide molecular tools to assist breeders in developing resistant cucumbers.

Agrobacterium infectious clones of CuLCrV have been developed for phenotyping watermelon and other susceptible vegetable crops for resistance. The clones will be used to phenotype the watermelon core collection available with USDA and sources of resistance will be identified for use in breeding programs.

We will cross the M. enterolobii resistant pepper line PMER-2 with the M. incognita resistant 'Charleston Belle' and develop populations to assess the inheritance pattern of M. enterolobii resistance. If resistance from PMER-2 is simply inherited, wewill be able to select M. enterolobii resistant breeding lines. Development of new RKN resistant pepper lines with resistance against both the invasive M. enterolobii and the endemic RKN species will provide valuable tools to help pepper growers in southern U.S. to manage these pests in the field. 

We will conduct side-by-side developmental embryogenesis assays with M. enterolobii and M. incognita over a range of temperatures to compare the thermal developmental profiles of these two species and for the first time calculate an estimate of the thermal base temperature and optimal thermal temperature for  M. enterolobii. A greater understanding of the thermal factors that underlie the development in M. enterolobii will provide insight into the growing regions in the U.S. that may be threatened by this nematode as it continues to spread.

We have a large collection of isolates of cucurbit powdery mildrew pathogen collected from accross the U.S. This collection will be genotyped using simple sequence repeat(SSR) markers developed based on an available sequence and used to characterize diversity among the pathogen population.


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