Powdery scab of potato

Disease of Potato
By S. Sankareshwari

1. POWDERY SCAB OF POTATO COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po), ViaVaigai Dam, Theni-625 562 STUDENT Miss. SANKARESHWARI .S ID. No: 2015021115 COURSE TEACHER Dr. PARTHASARATHY S Asst. Professor (Plant Pathology)

2. Powdery Scab of Potato Spongospora subterranea f.sp . s ubterranea ( Wallr .) Lagerheim (1892)

3. History In 1842, Wallroth described the symptoms for the first time in the scientific literature in Germany. He called it as Erysibe subterranea . In 1887, Brunchhorst named the pathogen Spongospora solani . In 1892, Lagerheim proposed the name Spongospora subterranea Wallr .

4. Occurrence It was first discovered in Germany in 1842. It was found in Norway and England in 1846 and in U.S.A. in 1913 . It occurs in cooler areas of Australia, Tasmania, New Zealand and Kenya. Its occurrence in India is restricted to higher hills of Himachal Pradesh, Darjeeling and Nilgiris in south.

5. Economic Significance It is the second most important disease incited by a member of class Plasmodiophoromycetes . Economically significant soil-borne plant pathogen which is also important as a vector of a virus, the potato mop-top furovirus . They reduces the proportion of marketable production and carry infections to subsequent crops when used as seeds.

6. Host Plants Underground parts of Tomato. Other species of Solanum including S. nigrum and S. curtilobum . Carrot, Cabbage, Celery, Beans and Peas, Onion, Kikiyu , Cucumber, Maize and Solanaceous weeds.

7. Symptoms Attacks roots, stems, stolons and tubers. Young tubers- Purplish-brown lesions that later develop into small blisters occurring as early as 43 DAP. Mature symptoms- Round, slightly raised usually shallow lesions which shows raised margins. Root galls are creamy white and turns dark brown when they mature.

8. http://www.ag.ndsu.edu/publications/crops/powdery-scab-of-potatoes/pp1891.pdf

9. Taxonomic classification Phylum: Cercozoa Class: Phytomyxea Order: Plasmodiophorales Family: Plasmodiophoraceae Genus: Spongospora Species: Spongospora subterranea

10. Pathogen Obligate pathogen. Forms zoospores that swim in free water which penetrate the root hairs. They are uninucleate and on increase in size becomes multinucleate Plasmodium. Forms spore balls that can survive in the soil for long periods of time. Vector of the mop-top virus.

11. PATHOGEN ON ROOT HAIRS http://www.researchgate.net http:// people.ohio.edu

12. Mode of Spread Primary spread : Spore ball present in the soil. Secondary spread : Zoospores released from the resting spore.

13. Favourable conditions Free water is a prequisite for zoospores to cause infection. Cool conditions: ±12 – 17ºC are optimal for the infection of tubers. Spore ball germination- 10ºC.

14. Life Cycle http ://extension.umaine.edu/publications2436e/

15. Management Selection of healthy seed tubers. Avoid contaminated fields and excessive Nitrogen. Treatment of tubers with organomercurial fungicides. Use resistant varieties- S. tuberosum (CP 1742, 8-7), S. tuberosum × S. andigena (66-528/8, 66-587/4, 66-619/4, 66-669/1), S. tuberosum × S. microdontum (BRB/A-24) and a polyploid of S. tuberosum (JHT/A-1214). Resistant exotic varieties- Panther, Patron and Red Skin.