Linkage of random amplified polymorphic DNA markers to downy mildew resistance in cucumber (Cucumis sativus L.)

Marker assisted selection (MAS) may improve the efficiency of breeding downy mildew resistant cucumber cultivars. A study was conducted to identify random amplified polymorphic DNA (RAPD) markers linked to the downy mildew resistance gene ( dm) which would be suitable for MAS. A total of 145 F-3 families from two populations (55 from the WI 1983G x Straight 8 population and 90 from the Zudm1 x Straight 8 population) were evaluated over five locations in North America and Europe. Resistant and susceptible F-3 families were identified and mean family resistance ratings were used to type individual F-2 plants. No evidence for race differences in the pathogen ( Psuedoperonospora cubensis (Berk. & Curt.) Rostow) between North America and Europe was found. Phenotypic correlations between locations ranged from 0.3 to 0.7. Of the 135 polymorphic RAPD markers identified from 960 primers, five were linked to dm - G14(800), X15(1100), AS5(800), BC519(1100), and BC526(1000). In the WI 1983G x Straight 8 population, G14(800) was linked to dm at 16.5 cm, AS5(800) at 32.8 cm, BC519(1100) at 9.9 cm, and BC526(1000) at 19.2 cm. In the Zudm1 x Straight 8 population, G14(800) was linked at 20.9 cm, X15(1100) at 14.8 cm, AS5(800) at 24.8 cm, and BC526(1000) at 32.9 cm. Markers G14(800) and BC519(1100) were linked in repulsion to the dm allele, and X15(1100), AS5(800), and BC526(1000) were linked in coupling phase. These genetic markers may be exploited to develop an efficient MAS strategy for breeding resistant cucumber cultivars.