QTL Analysis of Disease Resistance in Interspecific Hybrid Grapes

Abstract

Quantitative trait loci (QTL) were mapped in an interspecific cross between two grape genotypes, 'Horizon' ('Seyval' x 'Schuyler') and Illinois 547-1 (V. cinerea x V. rupestris). A separate map for each parent was used for QTL analysis. Resistance to five grape diseases (Uncinula necator, Plasmopara viticola, Guignardia bidwellii, Botrytis cinerea, and Phomopsis viticola) was scored among the seedlings and analyzed by both single marker and interval analysis, using the program QGene. One major QTL (LOD=6.6) was found for powdery mildew resistance on the Ill. 547-1 map, the resistant parent. Two other QTLs for powdery mildew resistance were found on the 'Horizon' map. Coincidentally, the same three QTLs for powdery mildew were also associated with black rot resistance but to different degrees. One of the QTLs in 'Horizon' was also associated with production of the phytoalexin resveratrol in leaf discs. No significant QTLs were found for downy mildew resistance and only minor QTLs were found for the other traits. The presence of major effect QTLs, at least for powdery mildew and black rot, suggests the existence of some major genes or gene clusters are involved. Some limitations in detecting QTLs can be attributed to the small population size (58 individuals) and to the heterozygous nature of QTL mapping design.