DOWNY MiLDEW FUNGI part 2.pptx

DOWNY MILDEW FUNGI GENERA INCLUDES BREMIA AND PLASMOPARA,


Downy mildew fungi are plant pathogens that cause significant damage to a variety of crops, including grapes, cucumbers, lettuce, and onions. These fungi thrive in cool, moist environments and can spread rapidly through a field, causing devastating losses for farmers.

This slide deck provides an overview of downy mildew fungi, including their life cycle, symptoms, and management strategies. The presentation begins with an introduction to the various types of downy mildew fungi, including the species that affect grapes, cucumbers, and other crops.

Next, the slides detail the life cycle of downy mildew fungi, from spore germination to the development of lesions on plant leaves. The presentation also explains how these fungi spread from plant to plant and from field to field, and highlights the conditions that favor their growth and reproduction.

The slide deck then goes on to describe the symptoms of downy mildew infection, including yellowing and wilting of leaves, stunted growth, and the development of characteristic downy white or gray spores on the undersides of leaves.

Finally, the presentation offers practical tips and strategies for managing downy mildew fungi, including cultural control measures such as crop rotation and sanitation practices, as well as chemical control methods such as fungicides.

Overall, this slide deck provides a comprehensive overview of downy mildew fungi and their impact on agricultural crops, as well as practical strategies for preventing and managing these devastating plant pathogens.

1. ANNAMALAI UNIVERSITY FACULTY OF AGRICULTURE DEPARTMENT OF PLANT PATHOLOGY PAT-501 MYCOLOGY GENERAL CHARACTERS AND LIFE CYCLE OF GENUS PERONOSPORA , PSEUDOPERONOSPORA, PLASMOPARA , BREMIA , SCLEROSPORA , PERONOSCLEROSPORA BY R.LOKESH I -M.sc.,Agriculture Plant pathology Annamalai university TOPIC: Part-2

2. GENERAL CHARACTERS OF PLASMOPARA P viticola made history in France in 1930 by devastating the grape vines . It is reported from India from all the grape growing areas. All the succulent parts are affected. Chlorotic patches appear on the upper surface of leaves making them brittle,which fall off in shreds. In humid weath r downy growths (sporangiophores) emerge on the lower leaf surface tendrils, pedicels, flowers, and fruits Infected fruits shrivel and mummify

3. Scientific classification Kingdom: Chromista Phylum: Oomycota Order: Peronosporales Family: Peronosporaceae Genus: Plasmopara Species: P. viticola Binomial name Plasmopara viticola (Berk. & M.A. Curtis) Berl . & De Toni, (1888) DOWNY MILDEW OF GRAPES Plasmopara viticola , the causal agent of grapevine  downy mildew , is a  heterothallic   oomycete  that overwinters as  oospores  in leaf litter and soil.  Plasmopara viticola , also known as grape downy mildew, is considered to be the most devastating disease of grapevines in climates with relatively warm and humid summers. It was first observed in 1834 by Schweinitz on  Vitis aestivalis  in the southeastern United States

4. Downy mildew on upper (left) and lower (right) surface of grape leaves

5. SYMPTOMS Leaves show pale yellow spots on the upper surface with white downy growth of the fungus on the corresponding lower surface . Later, fungal growth becomes dirty grey and spot becomes brown (necrosis). Necrotic lesion coalesces to form larger patches resulting in defoliation. Downy growth on the shoots and tendrils leads to distortion and death of twigs. Infected flowers and berries will dry. Half grown infected berries become leathery, wrinkle and develop a reddish marbling to brown discoloration .

6. SYMPTOMS Leaves show pale yellow spots on the upper surface with white downy growth of the fungus on the corresponding lower surface . Later, fungal growth becomes dirty grey and spot becomes brown (necrosis). Necrotic lesion coalesces to form larger patches resulting in defoliation. Downy growth on the shoots and tendrils leads to distortion and death of twigs. Infected flowers and berries will dry. Half grown infected berries become leathery, wrinkle and develop a reddish marbling to brown discoloration .

7. *This devastating disease led to the unexpected accidental discovery of Bordeaux mixture by Millardet . *Bordeaux mixture (also called  Bordo Mix ) is a mixture of  copper(II) sulphate  (CuSO 4 ) and  quicklime  ( Ca O ) used as a  fungicide . It is used in vineyards, fruit-farms and gardens to prevent infestations of  downy mildew ,  powdery mildew  and other fungi. Bordeaux mixture in preparation

8. 1885 – The First Foliar Fungicide Eight decades passed before a method of controlling foliar disease was discovered; in 1885, P. M. A. Millardet described the effective use of a mixture of copper sulfate and lime for control of downy mildew on grapevines.

9. LIFE CYCLE Asexual reproduction Mycelium is hyaline, coenocytic, intercellular and produced globose haustona . Hyaline sporangiophores (4 - 6 or more) arise from the hyphae in sub stomatal spaces / stomata in the lower surface of the leaves / lenticels (in case of fruits) Sporangiophores branch almost at right angle to the main axis and at regular intervals. From each branch, 2 or 3 secondary branches arise in a similar manner . From the apex of each secondary branch, 2 3 sterigmata arise to bear hyaline. Single celled, lemon shaped and thin sporangia singly. Sporangia germinate and produce zoospores (biflagellate), which encyst and germinate to put forth mycelium.

10. Sexual reproduction The fungus is heterothallic and hence two mating types (P1 and P2) must be present for sexual reproduction. Spherical, thick, dull brown oospores are formed later in the infected area due to the union of antheridium and oogonium. Oospores germinate after a period of rest and produce zoosporangium. Zoospores are released from the sporangium , which start further infection by putting forth germ tube.

11.      Sporangium and spores of  Plasmopara viticola       Lemon-shaped sporangia of  Plasmopara viticola  

12. GENERAL CHARACTERS OF BREMIA Bremia lactucae  is a plant pathogen. This microorganism causes a disease of lettuce ( Lactuca sativa ) denominated as  downy mildew . Some other strains can be found on 36 genera of Asteraceae including  Senecio  and  Sonchus . Experiments using sporangia from hosts do not infect lettuce and it is concluded that the fungus exists as a quantity of host-specific strains ( formae speciales ). Wild species, such as  Lactuca serriola , or varieties of  Lactuca  can hold strains that infect lettuce, but these pathogens are not sufficiently common to seriously infect the plant.

13. Common name  Lettuce downy mildew Scientific name   Bremia lactucae Plants affected  Lettuces Main symptoms  Yellow blotches and white mould on leaves Caused by  Fungus-like (Oomycete) organism Timing  Indoors any season, outdoors early summer until mid-autumn Lettuce downy mildew

14. Symptoms and Signs Downy mildew causes light green to  yellow angular spots  on the upper surfaces of leaves. The white  fluffy growth  of the pathogen develops on the lower sides of these spots. With time these lesions turn brown and dry up. Older leaves are attacked first. Severely infected leaves may die. On rare occasions the pathogen can become systemic, causing dark discoloration of stem tissue. If downy mildew infects the cotyledons of young seedlings, the plants can die. Greenhouse-grown lettuce transplants can also be infected.

15. SYMPTOMS PHOTOS

16. REFERENCES https://www.apsnet.org/edcenter/disandpath/oomycete/pdlessons/Pages/DownyMildewGrape.aspx https://en.wikipedia.org/wiki/Plasmopara_viticola#:~:text=Plasmopara%20viticola%2C%20also%20known%20as,in%20the%20southeastern%20United%20States . Introductory mycology – Alexopoulos An introduction to fungi – H.Dube https://en.wikipedia.org/wiki/Bremia_lactucae