Downy Mildew of sorghum

Disease of Sorghum - Leaf Shredding Disease caused by Peronosclerospora sorghi

1. DOWNY MILDEW OF SORGHUM COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai Dam, Theni-625 562 STUDENT Miss. DHANUJA N ID. No. 2015021029 COURSE TEACHER Dr. PARTHASARATHY S Asst. Professor (Plant Pathology)

2. DOWNY MILDEW OF SORGHUM OTHER NAME: Leaf shredding disease LOCAL NAME: Adi S aambal N oi (Tamil) COMMON NAME: Mildew of Maize and Sorghum

3. CASUAL ORGANISM : Peronosclerospora sorghi (W . Weston & Uppal ) C.G. Shaw Both oospore and conidia cause infection.

4. IMPORTANCE: Sorghum downy mildew (SDM) is a highly destructive disease caused by the soil borne fungus Peronosclerospora sorghi. It can have a significant economic impact, as infection results in plant death or lack of grain formation in the panicle.

5. HISTORY: P . sorghi was introduced to the Americas in the mid to late 1950s, probably in the Central American region, possibly Panama (Toler et al ., 1959; Futrell , 1974). It reached the USA in the early 1960s (Reyes et al ., 1964) and has subsequently spread to many other countries in Central and South America.

6. HISTORY: P . sorghi is widespread in Africa and Asia (Williams, 1984; Jeger et al ., 1998). It is thought that the pathogen co-evolved on sorghum in Africa (Williams, 1984) although other theories suggest Asia (Shaw, 1981; Weltzein , 1981 ). It can be considered endemic on these two continents.

7. ECONOMIC IMPORTANCE: The economic impact can be substantial as systemically infected plants are generally sterile . This is demonstrated by the epidemics of sorghum downy mildew in Venezuela in the early 1970s, which resulted in the epidemic being declared a national emergency (El Nacional , Venezuela, August 2, 1975, in Frederiksen and Renfro, 1977).

8. ECONOMIC IMPORTANCE: Losses of US$ 2.5 million were caused in the coastal counties of Texas, with incidence in individual fields reaching 90% ( Frederiksen et al., 1969). In India, Payak ( 1975) reported losses of 100,000 metric tons.

9. DISTRIBUTION: WORLD: P. sorghi exists in Africa, the Indian sub-continent, South-East Asia and North, Central and South America. INDIA: Andhra Pradesh, Delhi, Haryana, Karnataka, Kerala, Madhya Pradesh, Maharastra , Rajasthan, Tamil Nadu.

10. DISTRIBUTION © https://www.plantwise.org

11. SYMPTOMS: There are two types of symptom produced by P. sorghi in both sorghum and maize ( Schuh et al ., 1986). Systemic infection which occurs by oospores or conidia during the first four weeks of germination of the seed. Local lesions resulting from conidial infection of older plants, which may also give rise to systemic infection.

12. SYMPTOMS: The fungus invades the growing points of young plants , either through oospore or conidial infection . As the leaves unfold they exhibit green or yellow colouration. Abundant downy white growth is produced on the lower surface of the leaves , which consists of sporangiophores and sporangia .

13. SYMPTOMS : Normally three or four leaves develop the chlorotic downy growth. Subsequent leaves show progressively more of a complete bleaching of the leaf tissue in streaks or stripes. As the infected bleached leaf matures they become necrotic and the interveinal tissues disintegrate, releasing the resting spores (oospores ). This leaves the vascular bundles loosely connected to give the shredded leaf symptom.

14. Pale yellow to light colored streaked appearance © pioneer.com

15. P arallel stripes of green and white tissues © pioneer.com

16. S hredded appearance © pioneer.com

17. White (downy) growth on the underside of leaf © pioneer.com

18. Chlorotic streaks on leaves ©Rob Williams/CAB International

19. SYSTEMATIC POSITION Domain : Eukaryota     Kingdom: Chromista         Phylum: Oomycota             Class: Oomycetes                 Order: Sclerosporales                     Family: Sclerosporaceae                         Genus: Peronosclerospora                             Species: P. sorghi

20. PATHOGEN: Personosclerospora sorghi has a polycyclic disease cycle. It is capable of causing secondary infection of the susceptible hosts throughout the growing season.

21. Asexual phase: Conidia (15.0-28.9 x 15.0-26.9 µm) are hyaline, thin-walled and suborbicular . Some conidia are in the process of germinating by a single, unbranched hyphal germ-tube . Sexual phase: Oospores (31.0-36.9 µm) are thick-walled and spherical.

22. ©icrisat.org Asexual phase Mature conidiophore

23. OOSPORE: ©icrisat.org

24. FAVOURABLE CONDITIONS: Relative humidity 100%. Optimum temperature 21-23°C. Light drizzling. Cool weathers.

25. MODE OF SPREAD: Primary Infection : Oospores present in the Soil, Mycelium, Seeds. Secondary Infection: A ir-borne sporangia.

26. LIFE CYCLE: The oospores are present in the soil when the host seedlings are germinating. They infect the roots of the seedlings. This is a systemic infection. The pathogen grows throughout the plant, infecting the leaves as they grow, leading to chlorosis .

27. LIFE CYCLE: The chlorotic leaves develop white streaks. When the oospores become mature, the white streaks on the leaves turn brown and become necrotic. These necrotic areas become shredded over time, which is how the mature oospores are disseminated.

28. LIFE CYCLE: As the pathogen continues to develop in the host plant, there may also be production of conidia on the leaf surface. This cause the white, downy growth on the undersides of the leaves. After they are released, they are wind disseminated.

29. MANAGEMENT Cultural methods: Growing non-host or host crops (for example, oat, barley, flax, Sorghum sudanense or cowpea) for 15 days, and maize for 17 days reduced the inoculum potential in soils infested with oospores Deep tillage.

30. Biological Control: A Chytrid fungus ( Gaertneriomyces sp.) was identified parasitizing oospores of P. sorghi (Kenneth, 1982). It caused a reduction in the incidence by up to 58% by parasitizing the soil-inhabiting oospores (Kunene et al., 1990 ).

31. Botanical Control: Leaf extracts of Prosopis chilensis and Azadirachta indica have also shown to have some efficiency ( Kamalakannan and Shanmugam , 2009).

32. Resistant varieties: Grow moderately resistant varieties like Co25 Co26. Tolerant variety: P aiyur 2

33. Chemical Control: The fungicide Metaloxyl is efficient in reducing the systematic infection of downy mildew when applied as seed dressing. Seed treatment followed by two foliar sprays at 10 and 40 days after emergence completely controls the disease.