Abstract
The abundance of predatory phytoseiid mites, Typhlodromus pyri, important biological control agents of spider mite pests in numerous crops, is positively influenced by the density of leaf trichomes and tuft-form domatia in vein axils. Identification of the genetic regions controlling both trophic levels could facilitate the improvement of predatory mite habitat in breeding programs. The abundance of T. pyri and non-glandular trichomes was measured in a segregating F1 family derived from the cross of the complex Vitis hybrid, 'Horizon', with Illinois 547-1 (V. rupestris B38 × V. cinerea B9), finding positive correlation among traits. High density genetic maps were used to localize one major quantitative trait locus (QTL) on chromosome 1 of Illinois 547-1 associated with both predatory mite abundance and leaf trichomes. This QTL explained 23% of the variation in phytoseiid abundance and similar amounts of variance in domatia rating (21%), domatia size (16%), leaf bristle density (37% in veins and 33% in blades), and leaf hair density (20% in veins and 15% in blades). Another nine QTL distributed among chromosomes 1, 2, 5, 8, and 15 were associated solely with trichome density, and explained 7-17% of the phenotypic variation. Combined, our results provide evidence of the genetic architecture of non-glandular trichomes in Vitis, with a major locus influencing trichome densities, domatia size and predatory mite abundance. This information is relevant for breeding grapevines with a more favorable habitat for biological control agents.