Rgb3: an organ-specific QTL for bunch resistance to black rot identified in the hybrid cultivar ‘Merzling’ Hands-on demo of the potential of Grapedia

Crops are continuously exposed to the onset of emerging diseases and the exploitation of resistance donors in breeding programs is a widely used valid strategy. In the last two decades black rot (BR), caused by the ascomycete Phyllosticta ampelicida (syn. Guignardia bidwellii), has begun to threaten European viticulture in humid continental areas due to the advent of higher temperatures which favor the pathogenic cycle of the fungus. For this reason, a program has been established for the dissection of BR resistance trait and its introgression both in Vitis vinifera varieties and mildew resistant hybrids. A preliminary study was carried out to improve germplasm screening through different approaches. Historical phenotypic and pedigree information of resistance donors were gathered to support the decision-making process in breeding. A new propagation and inoculation strategy was developed to optimize and fasten inoculation experiments. Isolates of P. ampelicida were genetically characterized and combined for the assessment of resistance independent of race-specificity. Finally, these improvements were employed first for the identification of new BR resistant parental lines and breeding selections, and then for the quantitative trait locus (QTL) analysis in a segregating population derived from the cross ‘Merzling’ (hybrid, resistant) × ‘Teroldego’ (V. vinifera, susceptible). The screening of this progeny, under green-house and field conditions, allowed the discrimination between two distinct organ-specific QTLs on chromosome 14. The previously identified Resistance to G. bidwellii (Rgb)1 locus was confirmed associated with leaf/shoot resistance, while upstream a new QTL designated Rgb3 was discovered linked to bunch resistance. Driven and inspired by the INTEGRAPE community effort that led to GRAPEDIA (GRAPEvine -omics encyclopDIA), all the available tools and resources have been exploited for the exploration of the physical region of the two QTLs, providing a hands-on demo of the potential of this portal.