Phenotypic and genotypic assessment of black rot resistance in a grapevine diversity panel

Abstract

Black rot, caused by the ascomycete Guignardia bidwellii (anamorph Phyllosticta ampelicida), is an important fungal disease of grapevine (Vitis vinifera L.) and can lead to severe yield losses, particularly under warm and humid conditions. While genetic resistance represents a promising strategy for sustainable disease management, the diversity and distribution of black rot resistance within cultivated germplasm are still insufficiently characterized.

In this study, we investigated black rot resistance in a comprehensive diversity panel maintained at Hochschule Geisenheim University (HGU). The panel includes a wide range of international cultivars, traditional and historical varieties, as well as fungus resistant cultivars (PIWIs).

The experiment was conducted as a randomized block design across independent inoculation runs. Each genotype was tested in a single run with three biological replicates, arranged in three spatial blocks in the greenhouse. Fifteen control genotypes were included in all runs to account for temporal variation between inoculation dates. Plants were inoculated with conidia of P. ampelicida, and disease response was assessed after the end of the incubation period by visual scoring of disease severity and characterization of symptoms on leaves and shoots (lesion size, coloration, and overall symptom morphology). In parallel, selected accessions were screened for the presence of known black rot resistance alleles at the Rgb1 and Rgb3 loci using molecular markers.

The overall aim of this project is to systematically evaluate the level of black rot resistance across a broad and genetically diverse grapevine collection. By combining phenotypic and genotypic data, we seek to determine whether observed resistance patterns can be explained by previously described resistance loci or whether additional, potentially novel sources of black rot resistance are present. This study provides a systematic phenotypic and genotypic baseline that will serve as a foundation for future genetic analyses and breeding efforts aimed at improving black rot resistance in grapevine.