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Title: QTL mapping for downy mildew resistance in cucumber inbred line WI7120 (PI 330628)

Author
item WANG, YUHUI - University Of Wisconsin
item VANDENLANGENBERG, KYLE - North Carolina State University
item WEHNER, TODD - North Carolina State University
item KRAAN, PETER - Nunhems Seeds
item SUELMANM, JOS - Nunhems Seeds
item ZHENG, XIANGYANG - Magnum Seeds Inc
item OWENS, KEN - Magnum Seeds Inc
item Weng, Yiqun

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2016
Publication Date: 5/4/2016
Publication URL: http://handle.nal.usda.gov/10113/5372619
Citation: Wang, Y., VandenLangenberg, K., Wehner, T.C., Kraan, P.A.G., Suelmanm, J., Zheng, X., Owens, K., Weng, Y. 2016. QTL mapping for downy mildew resistance in cucumber inbred line WI7120 (PI 330628). Theoretical and Applied Genetics. 129(8):1493-1505. doi: 10.1007/s00122-016-2719-x.

Interpretive Summary: Downy mildew (DM) caused by the obligate oomycete Pseudoperonospora cubensis is the most devastating fungal disease of cucumber worldwide. The molecular mechanism of DM resistance in cucumber is poorly understood, and use of marker-assisted breeding for DM resistance is not widely available. Here we reported QTL mapping results for DM resistance with 243 F2:3 families from the cross between DM resistant inbred line WI7120 (PI 330628) and susceptible ‘9930’. A linkage map was developed with 348 SSR and SNP markers. Phenotyping of DM inoculation responses were conducted in four field trails in two years at three locations. Four QTL, dm2.1, dm4.1, dm5.1 and dm6.1 were consistently and reliably detected across the four environments which together could explain 62-76% phenotypic variations (R2). Among them, dm4.1 and dm5.1 were major-effect QTL (R2=15-30%) with only additive effects; dm2.1 (R2=5-15%) and dm6.1 (R2=4-8%) had moderate and minor effects, respectively. Epistatic effects were detected for dm2.1 and dm6.1 with both dm4.1 and dm5.1. One additional minor-effect QTL, dm6.2 (R2=3-5%) was only detectable with the chlorosis rating criterion. All alleles contributing to DM resistance were from WI7120. This study revealed two novel QTL for DM resistance and the unique genetic architecture of DM resistance in WI7120 conferring high level resistance to prevailing DM populations in multiple countries. The effects of disease rating scales, rating time and criteria, population size in phenotyping DM resistance on the power of QTL detection, and the use of DM resistance in WI7120 in cucumber breeding were discussed.

Technical Abstract: Downy mildew (DM) is the most devastating fungal disease of cucumber worldwide. The molecular mechanism of DM resistance in cucumber is poorly understood, and use of marker-assisted breeding for DM resistance is not widely available. Here we reported QTL mapping of DM resistance with 243 F2:3 families from the cross between DM resistant inbred line WI7120 (PI 330628) and susceptible ‘9930’. A linkage map was developed with 348 SSR and SNP markers. Phenotyping of DM inoculation responses were conducted in four field trails in two years at three locations. Four QTL (dm2.1, dm4.1, dm5.1 and dm6.1) were consistently and reliably detected across the four environments which together could explain 62-76% phenotypic variations. Among them, dm4.1 and dm5.1 were major-effect QTL (R2=15-30%) with only additive effects; dm2.1 (R2=5-15%) and dm6.1 (R2=4-8%) had moderate and minor effects, respectively. Epistatic effects were detected for dm2.1 and dm6.1 with both dm4.1 and dm5.1. One additional minor-effect QTL, dm6.2 (R2=3-5%) was only detectable with the chlorosis rating criterion. All alleles contributing to DM resistance were from WI7120. This study revealed two novel QTL for DM resistance and the unique genetic architecture of DM resistance in WI7120 conferring high level resistance to prevailing DM populations in multiple countries. The effects of disease rating scales, rating time and criteria, population size in phenotyping DM resistance on the power of QTL detection, and the use of DM resistance in WI7120 in cucumber breeding were discussed.