1a.Objectives (from AD-416):
1) Develop a SNP-based high-resolution genetic map through genotyping by sequencing in a recombinant inbred line population;
2) Develop an integrated, high-resolution genetic-physical map with SSR and SNP markers in cucumber;
3) Conduct QTL mapping of different sources of resistance against the new downy mildew strain and powdery mildew.
1b.Approach (from AD-416):
1) Development of SNP- and SSR-based high-resolution genetic map:
a. Develop a mapping population with 175 RILs from Gy14 × 9930 mating
b. SNP genotyping of this population by re-sequencing
c. Develop a SNP- and SSR-based high-resolution linkage map with this population
d. Anchoring cucumber draft genome scaffolds onto this genetic map to develop an improved chromosome-level genome assembly;
2) QTL mapping of downy mildew and powdery mildew resistances:
a. Resistance sources: PI 197088, PI 330628, Gy14 (dm-1)
b. Mapping populations: F2 and F2:3 from different crosses
c. Phenotyping: greenhouse artificial inoculation, and field trials (both ARS and sponsor)
d. Genotyping: SSRs, indels, SNP-based CAP, dCAPS
e. Fine mapping of major QTL for downy mildew and powdery mildew resistances, and clarify the linkage relationships of major QTLs for the two resistance genes.
This project was renumbered from 3655-21000-048-56T to 3655-21000-062-24T. A high-density genetic map is under construction to develop an integrated genetic-physical map for cucumber. An F2:3 mapping population has been developed for quantitative trait loci (QTL) mapping of downy mildew (DM) resistance in cucumber which consists of 250 F2:3 families from a cross between plant introduction line (PI) 330628 and 9930, a North China fresh market type. This population has been sent to our cooperator for field screening. A simple sequence repeat (SSR)-based linkage map is being developed for QTL mapping of DM resistance in PI 330628. Re-sequencing of the two parental lines is underway. The work relates to objective 2 in utilizing modern molecular technologies to discover genetic variations and to map agriculturally important disease resistance genes in cucumber.