2018 ASHS Annual Conference

Phylloxera has devastated the roots of wine grapes in Europe since the 19^th century. Major measures to control this pest include grafting European wine grape variety, Vitis vinifera, onto resistant American rootstocks and hybrid breeding. However, many hybrids such as ‘Frontenac’ are susceptible to the leaf-galling form of phylloxera. Limited studies have investigated foliar phylloxera, including its genetic resistance and resistance mechanisms. Antibiosis, antixenosis, and tolerance have been the classical resistance mechanisms that a plant uses to combat an insect pest. This study investigates the role of leaf trichome features (the presence, density, and type of hair on leaf) in resistance to foliar phylloxera, as a potential morphological antixenosis/non-preference mechanism. Two advanced hybrid grape breeding lines, MN1264 and MN1246, and a resulting F1 population, GE1025 (N = 125), are examined on a 0 to 5 scale for trichome density on leaf blade and vein of the adaxial and abaxial sides of the leaf, as well as on leaf edge and petiole. The type of trichome is also examined: ribbon, simple, or glandular. This population has previously been evaluated for leaf phylloxera severity and sequenced using genotype-by-sequencing with a major resistance QTL found on linkage group 14 (LG14). Preliminary results show that vein trichome density and petiole trichome density differ significantly between MN1264 and MN1246, compared with that of ‘Frontenac’ (susceptible) and ‘Louise Swenson’ (resistant) where vein, leaf, edge, and petiole trichome density differ significantly. Vein and petiole trichome type differ between MN1264 and MN1246, whereas vein, edge, and petiole trichome type differ between ‘Frontenac’ and ‘Louise Swenson’. Trichome density and type variation do exist in GE1025. The age and the side of the leaf measured might also play a role in contributing to trichome density differences. With these preliminary pieces of information, the population of GE1025 is under the process to be characterized for leaf trichome features, the relationship of which will be analyzed with foliar phylloxera severity (phenotypic correlation and coincidence of QTL). The significance of this study is to 1) develop a protocol to characterize leaf trichome in hybrid grape populations and 2) shed light on the underlying mechanisms of genetic resistance to phylloxera, whether leaf trichome plays a role, as high-resolution genetic mapping for resistance on LG14 is underway.