Local European Cultivars as Sources of Durable Scab Resistance in Apple

Abstract

The V f resistance gene has been widely used in apple breeding programmes to control Venturia inaequalis, the causal agent of scab, the major apple disease. Since the appearance of new strains that are able to overcome this major gene, research in Europe has been focused on durable resistance. The objective of one task of the European DARE project was to find cultivars which show a broad spectrum of resistance to the different scab races. This collaborative work involved 6 partners who tested 36 cultivars with various local scab inocula collected in the participating countries and with 8 monoconidial strains belonging to known races or isolated and characterized in the frame of the DARE project. Tests were performed each year from 1998 to 2001. Symptoms were assessed using macroscopic scoring scales. Some microscopic observations were performed; these resulted in a better knowledge of the host/pathogen interaction. Very diverse and complex resistance behaviours were found: the cultivars which showed the widest range of resistance were mostly local cultivars and some newly selected hybrids combining major genes and partial resistance. It would be worthwhile to include these individuals as parents in apple breeding programmes to improve the durability of scab resistance. Some methodologies and strategies to reach this goal will be proposed.

Variability of the Pathogenicity of Venturia Inaequalis in Europe

“…Three polygenic resistant hybrids ('Discovery', 'Durello di Forli', TN10-8) showed a good level of resistance in this test. For the first two cultivars, this result is in agreement with those of the greenhouse tests (Laurens et al, 2004).…”

European pome fruit genetic resources evaluated for disease resistance

“…An alternative approach is to incorporate partial resistances present in the germplasm (Lateur et al 2009). Laurens et al (2004) have screened local European cultivars as sources for durable scab resistance in apple. Glasshouse tests were carried out at different sites with a set of 36 varieties and subjected to inoculation with local inocula or with monoconidial strains.…”

“…This feature might be interesting also for a new, distinguishable commercial cultivar. Other interesting cvs include ''Dülmener Rosenapfel'' which has proved to be resistant to all scab inocula used in the trials of Laurens et al (2004), and ''Krimskoe'', and ''Korastojnka'' which originate from Ukraine and Bulgaria, respectively. These were introduced for their high level of polygenic scab resistance.…”

Inheritance studies of apple scab resistance and identification ofRvi14, a new major gene that acts together with other broad-spectrum QTL

“…Indeed, so far 'Gala' has been considered susceptible, regardless of the V. inaequalis isolate. For instance, Laurens et al (2003) tested the same isolates as those used in our experiment, except for isolate 301, and showed that 'Gala' was highly susceptible to all the tested isolates. Nevertheless, macroscopic and microscopic studies have shown that its level of susceptibility differs according to the fungal isolate (M. Chevalier, personal communication 2007).…”

“…After vernalization and when plant growth resumed, leaves were exposed to a second inoculation in autumn 2005. The parents could not be evaluated because they were not in the growth stage when their progeny and susceptible control individuals were inoculated, but they had been previously evaluated for their disease response in the same greenhouse by Laurens et al (2003).…”