Abstract
The downy mildew disease in grapevines is caused by Plasmopara viticola. This disease poses a serious threat wherever viticulture is practiced. Wild Vitis species showing resistance to P. viticola offer a promising pathway to develop new grapevine cultivars resistant to P. viticola which will allow reduced use of environmentally unfriendly fungicides. Here, transmission and scanning microscopy was used to compare the resistance responses to downy mildew of three resistant genotypes of V. davidii var. cyanocarpa, V. piasesezkii and V. pseudoreticulata and the suceptible V. vinifera cultivar ‘Pinot Noir’. Following inoculation with sporangia of P. viticola isolate ‘YL’ on V. vinifera cv. ‘Pinot Noir’, the infection was characterized by a rapid spread of intercellular hyphae, a high frequency of haustorium formation within the host’s mesophyll cells, the production of sporangia and by the absence of host-cell necrosis. In contrast zoospores were collapsed in the resistant V. pseudoreticulata ‘Baihe-35-1’, or secretions appeared arround stomata at the beginning of the infection period in V. davidii var. cyanocarpa ‘Langao-5’ and V. piasezkii ‘Liuba-8’. The main characteristics of the resistance responses were the rapid depositions of callose and the appearance of empty hyphae and the plasmolysis of penetrated tissue. Moreover, collapsed haustoria were observed in V. davidii var. cyanocarpa ‘Langao-5’ at 5 days post inoculation (dpi) and in V. piasezkii ‘Liuba-8’ at 7 dpi. Lastly, necrosis extended beyond the zone of restricted colonization in all three resistant genotypes. Sporangia were absent in V. piasezkii ‘Liuba-8’ and greatly decreased in V. davidii var. cyanocarpa ‘Langao-5’ and in V. pseudoreticulata ‘Baihe-35-1’ compared with in V. vinifera cv. ‘Pinot Noir’. Overall, these results provide insights into the cellular biological basis of the incompatible interactions between the pathogen and the host. They indicate a number of several resistant Chinese wild species that could be used in developing new cultivars having good levels of downy mildew resistance.
Highlights
Grapevine downy mildew is caused by the obligate biotrophic oomycete,[1] Plasmopara viticola (Berk and Curt.) Berlese and de
It forms a germ tube that penetrates the substomatal cavity. This germ tube swells into an infection vesicle.[6]
After an incubation period of several days,[5] sporangiophores emerge through the stomatum and form sporangia.[8]
Summary
This disease is one of the most serious threats faced by viticulture in most areas where grapes are grown. It forms a germ tube that penetrates the substomatal cavity. This germ tube swells into an infection vesicle.[6] A primary hypha appears from an infection vesicle and quickly develops branches and haustoria.[7] After an incubation period of several days (sometimes in as few as 4 days),[5] sporangiophores emerge through the stomatum and form sporangia.[8] At the end of autumn, numerous oospores form within fallen leaves and berries allowing P. viticola to overwinter.[9]
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