Grapes powdery mildew

PAT 401

1. GRAPES POWDERY MILDEW COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai Dam, Theni-625 562 STUDENT Miss. DONGRE PRATHIMA ID. No. 2015021033 COURSE TEACHER Dr. PARTHASARATHY S Asst. Professor (Plant Pathology)

2. Common name Powdery mildew Scientific name Erysiphe necator ( Uncinula necator )

3. Introduction Powdery mildew is an important disease of grapes worldwide. The disease generally is considered less economically important than black rot or downy mildew. Unlike black rot and downy mildew, the powdery mildew fungus does not require free water on the plant tissue surface to infect. Powdery mildew can result in reduced vine growth, yield, fruit quality, and winter hardiness. Varieties of  Vitis vinifera  and its hybrids generally are much more susceptible than American varieties.

4. History The focus of this research is the invasion history and population structure of the grape powdery mildew fungus,  Erysiphe necator  (formerly  Uncinula necator ), an obligate parasite of  Vitis  species that was introduced into Europe and eventually, all other wine producing regions of the world. Historical records support the hypothesis that the source of the introduction is eastern North America .

5. Powdery mildew was described on grapes in North America in 1834, prior to its discovery in Europe in 1845 . Eastern North America is the centre of origin for many wild species of  Vitis  that have relatively high levels of resistance to many diseases and pests of grapevines, including powdery mildew . After its introduction to Europe, grape powdery mildew was observed throughout all wine producing regions of the world, including California in 1859 and Australia in 1866 .

6.   Erysiphe necator  most likely dispersed long distances by the movement of grapevines, which were frequently traded between continents in the mid 1800's and later.  

7. OCCURRENCE Maharashtra, Karnataka, Andhra Pradesh, Gujarat, Tamil Nadu, Haryana, etc ..

8. SYSTEMATIC POSITION Domain: Eukaryota     Kingdom: Fungi         Phylum: Ascomycota            Class:Leotimycetes                      Order: Erysiphales                             Family: Erysiphaceae                                 Genus : Uncinula                                     Species: Uncinula necator

9. Symptoms Malformation and discolouration of affected leaves. Discolouration of stem to dark brown. Floral infection results in shedding of flowers and poor fruit set. Early berry infection results in shedding of affected berries. Powdery growth is visible on older berries and the infection results in the Cracking of skin of the berries.

10. It spread through air borne conidia. Through dormant mycelium and conidia present in the infected shoots and buds.

11. ©https://www.google.co.in/img On leaves

12. ©https://www.google.co.in/url On fruits

13. Pathogen and its charcteristics Its cleistothecia have several asci & coiled tip appendages. Cleistothecia of the fungus are usually formed by fertilization of ascogonia by anthridia during the sexual cycle. They become mature at late February or early March then germinate by giving asci and ascospores inside. Ascospores will dessiminate by wind to reach the susceptible organs for inducing infection. Asexual reproduction occurs by producing conidia that are easily disseminate by wind, insects and workers from infected plants to healthy plants.

14. ©https://www.google.co.in/url?sa=i&source=images Cleistothecia

15. Favourable Conditions Conidia germinate at optimum temperatures ranging from 10-35 °C but temperatures from 25-28 °C low but not high atmospheric relative humidity are necessary for mycelium growth and conidial production.

16. Disease Cycle Powdery mildew is a polycyclic disease (one which produces a secondary inoculum ) that initially infects the leaf surface with primary inoculum , which is conidia from mycelium, or secondary inoculum , which is an overwintering structure called a  cleistothecium . When the disease begins to develop, it looks like a white powdery substance. The primary inoculum process begins with an ascogonium (female) and antheridium (male) joining to produce an offspring.

17. This offspring, a young cleistothecium , is used to infect the host immediately or overwinter on the host to infect when the timing is right (typically in spring). To infect, it produces a conidiophore that then bears conidia. These conidium move along to a susceptible surface to germinate. Once these spores or conidia germinate, they produce a structure called a haustoria , capable of "sucking" nutrients from the plant cells directly under the epidermis of the leaf.

18. At this point, the fungi can infect leaves, buds and twigs that then reinfect other plants or further infect the current host. From this point, you see more white powdery signs of powdery mildew, and these structures produce secondary inoculum to reinfect the host with mycelium and conidia, or use the mycelium to produce primary inoculum to another plant.

19. Life cycle of Grapes powdery mildew ©https://www.google.co.in/url?sa=i&source=images

20. Integrated Disease Management Spray Wettable sulphur 0.25 % or Karathane 0.01 %. Select an open planting site with direct sunlight. Plant rows in the direction of the prevailing wind in order to promote good air circulation and faster drying of foliage and fruit. Prune and train vines properly in such as way as to reduce shading and increase air circulation.

21. Varieties differ greatly in their susceptibility to powdery mildew. Cabernet Franc, Cabernet Sauvigon , Chancellor, Chardonnay, Chelois , Merlot, Pinot blanc , Pinot noir, Riesling, Rosette, Rougeon , Sauvignon blanc , Seyval , Vidal 256 and Vignoles are all highly susceptible. On susceptible varieties, control is based on the use of properly timed applications of effective fungicides. Early season ( prebloom through bloom) control of primary infections caused by ascospores must be emphasized.