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ARS Home Southeast Area Charleston, South Carolina Vegetable Research Research





- Kousik, Chandrasekar - Shaker
- Rutter, William
- 2022
- 2021
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- Publications
- Plant Diseases (303)

Research Project: **Location:
                            Vegetable Research** Project Number: 6080-22000-029-000-D
                        
                        Project Type: In-House Appropriated Start Date: May 1, 2017
                        
                        End Date: Apr 11, 2022 **Objective:**
                        
                        1. Determine genetics of resistance to diseases and nematodes and develop molecular markers linked to resistance genes in vegetable crops with emphasis on cucurbit and solanaceous crops. 
Sub-objective 1.A. Determine inheritance of resistance to powdery mildew (Podosphaera xanthii) in watermelon and identify molecular markers closely linked to resistance genes.
Sub-objective 1.B. Determine the genetic basis of resistance to Phytophthora fruit rot in watermelon.
Sub-objective 1.C. Determine inheritance of resistance to watermelon vine decline caused by Squash vein yellowing virus (SqVYV) and identify molecular markers closely linked to resistance genes.
Sub-objective 1.D. Determine genetic basis of resistance to northern root-knot nematodes (Meloidogyne hapla) in pepper.

2. Develop and release cucurbit and solanaceous germplasm with resistance to diseases and nematodes. 
Sub-objective 2.A. Develop and release disease resistant (Phytophthora fruit rot and Powdery mildew) watermelon breeding lines.
Sub-objective 2.B. Develop sweet peppers (sweet banana and Cubanelle-types) with resistance to southern root-knot nematode (Meloidogyne incognita).
Sub-objective 2.C. Develop germplasm resources for cucumber with improved resistance to southern root-knot nematode (M. incognita).

3. Monitor, collect and characterize emerging cucurbit fungal pathogens to aid in improving management practices for growers and processors. **Approach:**
                        
                        This project will identify and develop cucurbit and solanaceous germplasm and breeding lines with enhanced resistance to diseases caused by fungal, viral and other plant pathogens. Specifically, resistant germplasm and breeding lines will be developed for managing major limiting diseases, including Phytophthora fruit rot, powdery mildew, watermelon vine decline, and root-knot nematodes (RKN). We will utilize conventional and contemporary resistance phenotyping and crop improvement techniques to accomplish our objectives. 

Populations of watermelon segregating for resistance to powdery mildew will be generated by crossing a highly resistant selection developed from a Citrullus lanatus var. lanatus accession with susceptible cultivars. Resulting populations will be phenotyped for reaction to powdery mildew and analyzed to determine inheritance of resistance. Molecular markers linked to resistance will be identified and used in marker assisted selection to develop resistant breeding lines. 

A recombinant inbred line (RIL) population from a cross between Phytophthora fruit rot resistant and susceptible lines will be developed and phenotyped for resistance, and the information will be used to determine genetics of resistance. Analysis of differentially expressed transcriptomes by RNA-Seq resulting from Phytophthora-watermelon fruit interactions will also be used to further elucidate the genetics of fruit rot resistance. Red fleshed RILs with resistance will be used to develop Phytophthora-resistant lines. 

Advanced watermelon lines resistant to vine decline caused by the whitefly-transmitted squash vein yellowing virus, (SqVYV) will be developed using known sources of resistance in wild watermelon accessions and by employing pure line selection. A watermelon vine decline (WVD) resistant line developed previously (392291-VDR) will be crossed with a susceptible commercial cultivar to develop segregating populations that can be assessed for disease response to determine inheritance of SqVYV resistance. 

Sweet banana and Cubanelle pepper types resistant to southern RKN will be developed by using conventional recurrent backcross breeding procedures to transfer the dominant ‘N’ gene, which confers resistance, from a bell pepper to the different sweet pepper types. Populations of pepper segregating for resistance to northern RKN will be developed by crossing a highly resistant pepper with a susceptible pepper cultivar. These populations will be phenotyped for resistance to northern RKN, and the data will be used to determine the mode of inheritance. 

Select cucumber accessions will be screened for resistance to southern RKN. Resistant selections will be advanced by multiple cycles of selfing and resistance screening to develop southern RKN resistant cucumber lines. 

Isolates of cucurbit powdery mildew will be collected from across the U.S. and used to infect cucurbit differentials to determine the prevalence of particular powdery mildew races.


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