Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Oral Communication Abstract

THE EU-DARE PROJECT: A PRELIMINARY MOLECULAR CHARACTERISATION OF A NEW SOURCE OF SCAB RESISTANCE IN APPLE

TARTARINI S., GENNARI F., PRATESI D., PALAZZETTI C., SANSAVINI S.

Dipartimento Colture Arboree (DCA-BO), Bologna University, Italy

Malus x domestica, apple, scab resistance, molecular map, QTL markers

The Vf gene conferring scab resistance was widely used in apple breeding throughout the world in the past century. Recent identification of new races of Venturia inaequalis that are able to overcome the Vf gene (Parisi et al., 1998) suggests that breeding strategies have to be modified to achieve a more durable resistance. In the framework of an EU project (D.A.R.E.), new sources of resistance, probably polygenic, are currently being investigated both at the phenotypic and molecular levels. DCA-BO is evaluating a partial scab resistance source identified in the Italian germplasm cultivar Durello di Forlì. This source of resistance was crossed with the English cultivar Fiesta and the level of resistance of each seedling of the progeny (180 seedlings) was evaluated (with the Chevalier et al., 1991 scale) using different conditions and inocula: (I) greenhouse screening using a mix of conidia from some susceptible cvs; (II) greenhouse screening using conidia collected from the rare lesions in leaves of the Durello di Forlì parent and (III) two-year field scoring in an untreated nursery. There is a good correlation between different scorings but there is a clear resistance class shifting towards susceptibility when using the inoculum specific to the Durello di Forlì parent.

Molecular maps of the two parents were also made mainly using well-spaced SSR markers (primers kindly provided by the C. Gessler group – ETH Zurich, Switzerland) and chosen on the base of their informativeness and wide distribution throughout the apple genome. AFLP and isozyme markers (S. Manganaris – PIN-Naoussa, Greece) were also used to fill in gaps between anchor SSRs. The resulting maps cover all 17 linkage groups of apple, although there are still some gaps in some genomic regions.

A single locus QTL analysis (Kruskall-Wallis test) was performed using all the available resistance data. In general, three putative major QTLs were identified in linkage groups 10 (from Durello di Forlì), 11 and 17 (from Fiesta). Other QTLs may be identified as the coverage of the genome is improved. Noteworthy is that there are at least two QTLs from the Fiesta parent, showing that this parent is also able to confer a certain degree of scab resistance, as confirmed by the fact that Fiesta never showed sporulating lesions either after artificial inoculation with the mixed local inoculum or in natural field conditions in Italy. The QTL in LG10 of Durello di Forlì is overcome when the scab inoculum is prepared using the Durello di Forlì scab, suggesting a close relationship between plant genotype and pathogen.