Breakdown of resistance to grapevine downy mildew upon limited deployment of a resistant variety

Abstract

BackgroundNatural disease resistance is a cost-effective and environmentally friendly way of controlling plant disease. Breeding programmes need to make sure that the resistance deployed is effective and durable. Grapevine downy mildew, caused by the Oomycete Plasmopara viticola, affects viticulture and it is controlled with pesticides. Downy mildew resistant grapevine varieties are a promising strategy to control the disease, but their use is currently restricted to very limited acreages. The arising of resistance-breaking isolates under such restricted deployment of resistant varieties would provide valuable information to design breeding strategies for the deployment of resistance genes over large acreages whilst reducing the risks of the resistance being defeated. The observation of heavy downy mildew symptoms on a plant of the resistant variety Bianca, whose resistance is conferred by a major gene, provided us with a putative example of emergence of a resistance-breaking isolate in the interaction between grapevine and P. viticola.ResultsIn this paper we describe the emergence of a P. viticola isolate (isolate SL) that specifically overcomes Rpv3, the major resistance gene carried by Bianca at chromosome 18. We show that isolate SL has the same behaviour as two P. viticola isolates avirulent on Bianca (isolates SC and SU) when inoculated on susceptible plants or on resistant plants carrying resistances derived from other sources, suggesting there is no fitness cost associated to the virulence. Molecular analysis shows that all three isolates are genetically closely related.ConclusionsOur results are the first description of a resistance-breaking isolate in the grapevine/P. viticola interaction, and show that, despite the reduced genetic variability of P. viticola in Europe compared to its basin of origin and the restricted use of natural resistance in European viticulture, resistance-breaking isolates overcoming monogenic resistances may arise even in cases where deployment of the resistant varieties is limited to small acreages. Our findings represent a warning call for the use of resistant varieties and an incentive to design breeding programmes aiming to optimize durability of the resistances.

Genetic Analysis of the Biosynthesis of 2-Methoxy-3-Isobutylpyrazine, a Major Grape-Derived Aroma Compound Impacting Wine Quality

“…Moreover, it should be noted that allelic variations for VvOMT3 and VvOMT4 exist between high-and low-IBMP-producing grapevine cultivars (Supplemental Table S1), suggesting that these genes could be used as molecular markers for breeding purposes. There is currently great interest in breeding new grapevine varieties resistant to diseases of major economic importance in viticulture (Peressotti et al, 2010). These breeding programs based primarily on resistance characters may also offer the opportunity to improve quality-related traits.…”

Structural, Functional, and Evolutionary Analysis of the Unusually Large Stilbene Synthase Gene Family in Grapevine

“…There is currently considerable interest in breeding new grapevine varieties resistant to diseases of major economical importance in viticulture. To this aim, resistant Vitis species from North America have been extensively crossed with various grapevine varieties to introgress resistance into the grapevine background (Peressotti et al, 2010). Recent work has shown that resistance to downy mildew in a grapevine segregating population is associated with stilbene accumulation (Malacarne et al, 2011).…”

An Extended Leaf Disc Test for Virulence Assessment in Plasmopara Viticola and Detection of Downy Mildew Resistance in Vitis

“…In our previously published system [7], a set of six host genotypes (two North American species, one European and three commercially used cultivars) was developed to achieve an improved assessment of strain diversity of the oomycete. In the present study, we broaden the characterization system by including The development of necrosis on a specific host reveals the presence of resistance genes [12][13][14] and the level of sporulation achieved by a strain is related to its aggressiveness [15]. Conventional evaluation systems used on P. viticola based on the amount of sporangia do not consider the necrotic reaction of the plant [16][17][18] or evaluate it in combination with the sporulation [13,19].…”