Revision of the Nomenclature of the Differential Host-Pathogen Interactions ofVenturia inaequalisandMalus

Abstract

The apple scab (Venturia inaequalis-Malus) pathosystem was one of the first systems for which Flor's concept of gene-for-gene (GfG) relationships between the host plant and the pathogen was demonstrated. There is a rich resource of host resistance genes present in Malus germplasm that could potentially be marshalled to confer durable resistance against this most important apple disease. A comprehensive understanding of the host-pathogen interactions occurring in this pathosystem is a prerequisite for effectively manipulating these host resistance factors. An accurate means of identification of specific resistance and consistent use of gene nomenclature is critical for this process. A set of universally available, differentially resistant hosts is described, which will be followed by a set of defined pathogen races at a later stage. We review pertinent aspects of the history of apple scab research, describe the current status and future directions of this research, and resolve some outstanding issues.

Venturia inaequalis resistance in local Spanish cider apple germplasm under controlled and field conditions

“…Initially, this resistance was attributed to the Rvi6 (previously Vf or HcrVf2) gene, but has since been demonstrated to be of a more complex nature (Hough et al 1953(Hough et al , 1970Bénaouf and Parisi 2000;Bus et al 2011). Nearly a century after the initiation of breeding programs to introduce scab resistance to apple, none of the several cultivars developed to date has had a major impact in the market and did not result in the displacement of the major susceptible cultivars (MacHardy 1996).…”

“…Therefore, efforts to obtain commercially viable apple cultivars with durable resistance(s) remain a major target for breeding programmes (Hartman et al 2000;Bowen et al 2011). To date, 17 gene-for-gene relationships between V. inaequalis and apple species have been identified (Bowen et al 2011;Bus et al 2011). Race (6) isolates, which overcome the resistance conferred by Rvi6, have been detected in different places in Europe, including the North of Spain (Parisi et al 2004;Martínez-Bilbao and Murillo 2005).…”

Occurrence of Venturia inaequalis races in Poland able to overcome specific apple scab resistance genes

“…The set of differential hosts has since been extended to include one for each of the scab resistance genes described in the new nomenclature system (Bus et al 2009). Over the following years, the set of differentiated hosts was modified and broadened by Bus et al (2011). The host h(11), represented by M. baccata jackii, was replaced by the genotype A722-7 (M. baccata jackii × 'Starking'), and four hosts were added to the set: h(14) (Dülmener Rosenapfel), h(15) (GMAL2473), h(16) (MIS op 93.051 G07-098) and h(17) ('Antonovka', APF22).…”

Characterization of the defence response to Venturia inaequalis in ‘Honeycrisp’ apple, its ancestors, and progeny

“…To date, 17+ R genes mediating Malus-V. inaequalis interactions have been described (Gessler et al, 2006;Bus et al, 2011;Jha et al, 2009). These genes each impart pathogen race-specific resistance following the gene-for-gene model first described by Flor (1956).…”

“…The HR in apple is conditioned by several previously described R genes including Rvi4 (Vh4 = Vx = Vr1), Rvi5 (Vm), Rvi7 (Vfh), Rvi10 (Va), Rvi15 (Vr2) and Rvi16 (Vmis) (Win et al, 2003;Galli et al, 2010;Bus et al, 2011). This "pin-point" reaction results from the rapid death and subsequent collapse of cells immediately surrounding the penetration site of the spore (Goodman and Novacky, 1994).…”