Grapes downy mildew

PAT401

1. COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai D Downy mildew of grapes Plasmopara viticola STUDENT Miss. DIBIYA JOSE.L ID. No. 2015021032 COURSE TEACHER Dr. PARTHASARATHY S Asst. Professor (Plant Pathology)

2. Introduction Downy mildew is a highly destructive disease of grapevines in all grape-growing areas of the world where there is spring and summer rainfall at temperatures above 10ºC (50ºF).

3. History Plasmopara viticola was first observed in Southeastern United States by Schweinitz in 1834 on Vitis aestivalis .

4. Occurrence and distribution France, Europe, North America, Algeria, Australia and all over grapes growing areas in World.

5. Symptoms on leaves Foliar symptoms appear as yellow circular spots with an oily appearance ( oilspots ) on leaves. Young oilspots on young leaves are surrounded by a brownish-yellow halo. This halo fades as the oilspot matures. Under favorable weather conditions, large numbers of oilspots may develop and coalesce to cover most of the leaf surface.

6. After suitably warm, humid nights, a white downy fungal growth (sporangia) will appear on the underside of the leaves and other infected plant parts. The disease gets its name " downy mildew" from the presence of this downy growth. In late summer and early fall, the diseased leaves take on a tapestry-like appearance when the growth of the pathogen is restricted by the veinlets .

7. On berries White downy sporulation beneath suspect oilspots or on shoots or fruit bunches. Infected parts of young fruit bunches turn brown, wither, and die rapidly. If infections occur on the young bunch stalk, the entire inflorescence may die. Developing young berries will either die or, if between 3 and 5 mm in diameter, become discolored.

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11. P athogen Plasmopara viticola - asexual, biflagellate zoospores, sexual oospores is a resting stage. Mycelium is aseptate . It is an obligate parasite, and it absorbs nutrients from the living host tissue via globose haustoria Sexual reproduction occurs through the fusion of antheridia and oogonia within the host tissue. Plasmopara viticola has only recently been shown to be heterothallic.

12. Oospores form a single germ tube terminating in a sporangium. Zoospores form within the sporangia and are then released. Zoospores germinate and penetrate the plant only through functioning stomata. Sporangia – Tree like sporangiophores, bearing white, lemon-shaped sporangia.

13. Sporangia @ apsnet.org

14. Life cycle ohioline.osu.eduohioline.osu.edu ohioline.osu.edu Ohionline.osu.edu ioline.osu.edu

15. Taxonomic classification Kingdom : Fungi Superphylum : Heterokonta Class : Oomycota Order : Peronosporales Family : Peronosporaceae Genus : Plasmopara Species : P. viticola

16. Favourable conditions Optimum temperature for disease development is 64 to 76 F (18 to 25 °C).

17. Mode of spread Primary spread : Oospores on plant debris Secondary spread : Air borne sporangia

18. Management Cultural practices: Well-drained sites with good air movement. Trellising systems and pruning can be used to manage the leaf canopy to minimize leaf wetness Sanitation is important. Remove dead leaves and berries from vines and the ground after leaf drop.

19. Chemical management Pre-infection fungicides include the copper-based fungicides, such as Bordeaux mixture and the Dithiocarbamates . Specific control for grapes downy mildew Cymoxanil , fosetyl -al, metalaxyl , fenamidone , Sulfamide , Mancozeb , Phosphonate, A zoxystrobin

20. Bordeaux mixture preparation Copper sulphate 1kg and lime 1kg in 100l of water

21. Reference Saha L.R,Handbook of Plant diseases,2002,Kalyani Publishers,New Delhi. T.S.Thind,Diseases of fruits and vegetables and their managemnet,Kalyani publishers ,New Delhi. https://www.apsnet.org/educenter/introp/lessons/fungi/Oomycetes/Pages/DownyMildewGrape.aspx.