Plasmopara viticola (Berk. et Curt.) Berl. and de Toni, the agent of downy mildew, is one of the most important pathogens of European grapevine ( Vitis vinifera L.). Extensive evaluation of cultivated grapevine germplasm has highlighted the existence of resistant phenotypes in the Georgian (Southern Caucasus) germplasm. Resistance is shown as a reduction in disease severity. Unraveling the genetic architecture of grapevine response to P. viticola infection is crucial to develop resistant varieties and reduce the impact of disease management. The aim of this work was to apply a genome-wide association (GWA) approach to a panel of Georgian-derived accessions phenotyped for P. viticola susceptibility and genotyped with Vitis18kSNP chip array. GWA identified three highly significant novel loci on chromosomes 14 ( Rpv29 ), 3 ( Rpv30 ) and 16 ( Rpv31 ) associated with a low level of pathogen sporulation. Rpv29 , Rpv30 , and Rpv31 loci appeared to be associated with plant defense genes against biotic stresses, such as genes involved in pathogen recognition and signal transduction. This study provides the first evidence of resistant loci against P. viticola in V. vinifera germplasm, and identifies potential target genes for breeding P. viticola resistant grapevine cultivars.

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Potential enhancement of mycoparasitic efficacy of Coniothyrium minitans and Microsphaeropsis ochracea through concomitant colonization of Sclerotinia sclerotiorum sclerotia was investigated, following observation that the two mycoparasites did not exhibit any mutual antagonism in dual culture assays. Simultaneous application of both mycoparasites increased sclerotia mortality in a temperature range from 16 to 26°C compared to single application, indicating a predominantly additive interaction. With increasing temperature the efficacy of M. ochracea decreased, but C. minitans was unaffected. Degradation of sclerotia by C. minitans proceeded slightly faster than with M. ochracea. Simultaneous colonization of sclerotia was studied at the histopathological level with mycoparasite strains transformed via Agrobacterium tumefaciens-mediated transformation (ATMT) with reporter genes encoding for DsRed and GFP. Sclerotia colonization followed by fluorescence microscopy revealed effective penetration of the sclerotial rind, growth and formation of pycnidia in the cortex and medulla by both antagonists, resulting in complete degradation of sclerotia within 25 days after single inoculation. Upon simultaneous inoculation, both antagonists concomitantly colonized the sclerotial tissue and independently formed pycnidia in the sclerotial medulla and on the sclerotial rind, demonstrating their ability to co-colonize the same host fungus. Although the individual growth of the two mycoparasites in dual inoculations was slightly delayed, the sclerotia degrading effects were additive, suggesting a complementary antagonistic interaction. The combined application of two different species of mycoparasites cooperating on the same host fungus and differing in temperature requirements may be advantageous for making biocontrol applications in the field less sensitive to varying environmental and host conditions.

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