Components of partial resistance to Plasmopara viticola enable complete phenotypic characterization of grapevine varieties

Abstract

Six components of partial resistance (RCs) were studied in 15 grapevine varieties with partial resistance to Plasmopara viticola: (i) infection frequency (ifR, proportion of inoculation sites showing sporulation), (ii) latent period (LP50, degree-days between inoculation and appearance of 50% of the final number of sporulating lesions), (iii) lesion size (LS, area of single lesions in mm 2), (iv) production of sporangia (SpoR, number of sporangia produced per lesion, and SpoR', number of sporangia produced per mm 2 of lesion), (v) infectious period (ip, number of sporulation events on a lesion), and (vi) infectivity of sporangia (INF, infection efficiency of sporangia produced on resistant varieties). Artificial inoculation monocycle experiments were conducted for a 3-year period on leaves collected at leaf development, flowering, and fruit development. Compared to the susceptible variety 'Merlot', the partially resistant varieties showed reduced ifR, longer Lp, smaller LS, fewer SpoR and SpoR', shorter ip, and lower INF. At leaf development, IFR, SPOR, and INF were higher and LP was shorter than at flowering and fruit development. RCs analysis through monocyclic experiments provides reliable assessments of the resistance response of grapevine accessions. The workload required for routine assessment in breeding programs could be reduced by measuring IFR and SPOR, while producing robust results. Downy mildew (DM) of grapevine is a serious disease caused by the obligate, biotrophic Oomycete Plasmopara viticola 1. P. viticola originated from North America, was introduced in Europe in the 1870 s 2 , and spread across the continent in the following years 1. The level of partial resistance to DM varies widely among Vitis species and cultivars 3,4. The Eurasian grapevine V. vinifera, which is widely cultivated for its agronomic and quality traits, is generally susceptible to DM, whereas Asian and American Vitis species (e.g., V. riparia and V. rupestris) show varying degrees of resistance 5 because of their coevolution with the pathogen. The partial resistance to P. viticola is conferred to grapevines by specific loci referred to as Rpvs (resistance to P. viticola) 6 ; partial resistance has also been found in V. vinifera germplasm 7. Breeding programs have been implemented based on the hybridization of American Vitis spp. with V. vinifera for the introgression of resistance genes into the domesticated background of V. vinifera. Some of the breeding lines, after several cycles of backcrossing, gained more than 80% of V. vinifera genetic background 8 , and incorporated one or more (pyramided) Rpvs. Some reports, which characterized partially resistant varieties under vineyard conditions, indicate a reduction in the speed of DM epidemics on resistant varieties in comparison with susceptible grapevine ones 9,10. Since the early 1900s, several partially resistant varieties with good grape quality and in some cases capable of producing a vinifera-like wine 11-13 have been selected and released by breeders. The resistance res...

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Integrating metabolomics and targeted gene expression to uncover potential biomarkers of fungal/oomycetes-associated disease susceptibility in grapevine

“…Several crossing lines inbreed with American Vitis species are currently commercialized as partially resistant varieties to fungal pathogens, e.g. Regent, Calardis Blanc, Solaris 8,9 .…”

Besides stem canker severity, oilseed rape host genotype matters for the production ofLeptosphaeria maculansfruiting bodies

“…So far, plant resistance is still only characterised during the epidemics, e.g. in grapevine (Bove & Rossi, 2020). However, pathogen life-cycle stages related to intercrop transmission, like the production of oospores in Plasmopara viticola, are starting to be evaluated (Delbac et al, 2019).…”

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