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The deposition of callose is a common plant defense response to intruding pathogens and part of the plant's innate immunity. In this study, eight grapevine callose synthase (CalS) genes were identified and characterized. To investigate biological function of CalS in grapevine against the infection of Plasmopara viticola, expression patterns of grapevine CalS family genes were analyzed among resistant/susceptible cultivars. After P. viticola infection, expression of CalSl, 3, 7, 8, 9, 10, and 11 were significantly modified among the grapevine cultivars. For example, the expression of CalS1 and CalS10 were greatly increased in downy mildew (DM)-immune Muscadinia rolimdifolia 'Carlos' and 'Noble'. Transient expression assay with promoters of the CalS1 and CalS10 genes confirmed that they were regulated by the oomycete pathogen P. viticola. CalS1 promoter activity was also significantly up-regulated by ABA in DM-immune M. rotundifolia 'Noble', but down-regulated in DM-susceptible Vilis vinifera 'Chardonnay'. The CalSl promoter, however, was also down-regulated by GA in 'Chardonnay', but not affected in 'Noble'. The promoter activity of CalS10 was significantly up-regulated by GA in 'Chardonnay', but not regulated by ABA at all. It is proposed that CalS1 and CalS10 were involved in grapevine defense against DM disease. [ABSTRACT FROM AUTHOR]

The putative center of origin of Plasmopara viticola, the causal agent of grape downy mildew, is eastern North America, where it has been described on several members of the family Vitaceae (e.g., Vitis spp., Parthenocissus spp., and Ampélopsis spp.). We have completed the first large-scale sampling of P. viticola isolates across a range of wild and cultivated host species distributed throughout the above region. Sequencing results of four partial genes indicated the presence of a new P. viticola species on Vitis vulpina in Virginia, adding to the four cryptic species of P. viticola recently recorded. The phylogenetic analysis also indicated that the P. viticola species found on Parthenocissus quinquefolia in North America is identical to Plasmopara muralis in Europe. The geographicdistribution and host range of five pathogen species was determined through analysis of the internal transcribed spacer polymorphism of 896 isolates of P. viticola. Among three P. viticola species found on cultivated grape, one was restricted to Vitis interspecific hybrids within the northern part of eastern North America. A second species was recovered from V. vinifera and V. labrusca. and was distributed across most of the sampled region. A third species, although less abundant, was distributed across a larger geographical range, including the southern part of eastern North America. P. viticola clade aestivalis predominated (83% of isolates) in vineyards of the European winegrape V. vinifera within the sampled area, indicating that a single pathogen species may represent the primary threat to the European host species within eastern North America. [ABSTRACT FROM AUTHOR]

The resistance and susceptibility of grapevines to downy mildew (DM) disease caused by Plasmopara viticola were compared among different cultivars/accessions belonging to Vitis vinifera, V. rotundifolia, and 10 oriental Vitis species. After inoculation with P. viticola pathogen, no symptom was found in V. rotundifolia grapevines at all, while oriental species V. davidii and V. piasezkii, like V. vinifera, were susceptible to DM disease. The other eight oriental Vitis species showed various resistance levels to DM disease. Intraspecific resistant variations were also observed in V. amurensis. Microscopy studies were conducted on various time courses after pathogen infection on grape leaves. P. viticola hyphae were not observed in V. rotundifolia cultivars, while symptoms with varying degrees of severity were observed among the Euvitis species. In general, the DM resistant oriental species showed a slower development of hypha and less formation of haustoria than DM susceptible V. vinifera grapevines. Cells with distinctive fluorescence were observed in V. rotundifolia and the oriental species V. pseudoreticulata, and callose deposits were observed in V. rotundifolia, V. pseudoreticulata, and V. amurensis grapevines. Based on the results of morphological observations and microscopy studies, we concluded that there were five levels of grapevine resistance to P. viticola pathogen: (I) immune, (ii) extremely resistant, (iii) resistant, (iv) partly resistant, and (v) susceptible. [ABSTRACT FROM AUTHOR]