This document summarizes several diseases that affect greater yam, including anthracnose caused by Colletotrichum gloeosporioides, various viruses transmitted by aphids such as yam mosaic virus, and the storage disease dry rot caused by Botryodiplodia theobromae. It provides details on the symptoms, pathogens, and management strategies for these important diseases of greater yam.

1. DISEASES OF GREATER YAM
COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore-3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562
STUDENT
Miss. SOUNDARI A
ID. No. 2015021121
COURSE TEACHER
Dr. PARTHASARATHY S
Asst. Professor (Plant Pathology)

2. DISEASES OF GREATER YAM
• Field diseases
Anthracnose - Colletotrichum gloeosporioides
Yam Mosaic Virus Disease
Yam mild mosaic virus
Chinese yam necrotic mosaic virus
Dioscorea alata poty virus
Dioscorea alata bacilliform virus
Dioscorea alata ring spot mottle virus
Concentric leaf spot disease- S. rolfsi
• Storage disease Dry rot - Botryodiplodia theobromae

3. Anthracnose - Colletotrichum gloeosporioides
• Distribution – world wide
History
• Simon(1983) reported that Anthracnose disease of yam has had a
considerable impact on yam production world-wide.
• First reported in Nigeria.
Pathogen
Anamorph - Colletotrichum gloeosporioides
Author - Penz & Sacc
Teleomorph - Glomerella cingulata
Author - Spauld. & H. Schrenk

4. Symptoms :
• Small dark brown or black lesion on the leaves, petioles and stems.
• The lesion is often surrounded by a chlorotic halo enlarged and coalesces,
resulting in extensive necrosis of the leaves and die-back of the stem.
• The withered leaves and stem die-back gave the plant a scorched
appearance hence the name 'scorch' disease.
@flickriver.com @plantvillage.psu.edu

5. Systematic position:
• Kingdom : Fungi
• Phylum : Ascomycota
• Class : Sordariomycetes
• Order : Incertae sedis
• Family : Glomerellaceae
• Genus : Colletotrichum
• Species : C. gloeosporioides
• Subspecies: C. gloeosporioides (Penz)

6. Pathogen :
• Single celled conidia, hyaline slightly curved with oil globule.
Asexual fruiting body acervuli.
Favourable conditions:
Optimum temp - 25-28 °C, pH range of 5.8 to 6.5 and high
humidity. Spores are released from acervuli when there is an
abundance of moisture. Colletotrichum is inactive in dry season.
• Primary spread – Through dormant mycelium and ascospores from
infected debris.
• Secondary spread – Through wind borne conidia.

7. IDM
Cultural method:
• Plant early, in August and September
• Do not weed when the plants are wet to avoid shaking spores from infected
to healthy leaves and stems.
• Interplant with maize; presumably this is to increase the spacing between
plants Collect and burn or bury debris after harvest.
• Do not plant yams in the same land as the last crop. Leave a break of 3 years.
• Resistant varieties are Kinabayo, Plimbite, Belep ,Oriental TDA 291, TDA
297
Chemical method:
Thiophenate methyl 0.2%, Picoxystrobin 0.1% and mancozeb 0.2%

8. Yam Mosaic Virus
Distribution - worldwide
History
• The virus was first isolated and characterised from Dioscoea
cayenensis from Ivory Coast in 1979.
Classification
• Order: Unassigned
• Family: Potyviridae
• Genus: Potyvirus
Mode of transmission - Aphids

9. Symptoms
• Vein banding, curling, mottling, green-spotting, flecking
and shoe string symptom.
@plantvillage.psu.edu @plantvillage.psu.edu

10. Yam mild mosaic virus
Genus: Potyvirus
Mode of transmission - Aphids
Symptom - Mild chlorotic mottling
Dioscorea alata poty virus
Symptoms - chlorosis vein banding, flecking and
leaf puckering except discolouration of lamina.
@plantvillage.psu.edu
@plantvillage.psu.edu

11. Dioscorea alata bacilliform virus
Classification
• Order: Unassigned
• Family: Caulimoviridae
• Genus: Badnavirus
Mode of transmission-Mealybug @researchgate.net
Symptom – Mimic symptom of Dioscorea alata potyvirus . Virus
is present always but the expression of symptom is very rare.
If it expresses , it seems as dark green patches.

12. Dioscorea alata ring spot mottle virus
• Distribution- Togo
• Genus – Potyvirus
• Mode of transmission- Aphid
• Symptom @researchgate.net
• Mottling, stunting, chlorotic necrotic ring spotting
followed by veinal necrosis and malformed leaves.

13. Chinese yam necrotic mosaic virus
Distribution - Japan
Classification
• Order: unassigned
• Family: Potyviridae
• Genus: Macluravirus @6-sciencecentral.org
Mode of transmission- Aphid
• Mosaic and necrotic line patterns on the leaves
accompanied by stunting of the whole plants.

14. Management
• Good soil fertility could also minimize the effect of mosaic virus.
• Affected plants should be uprooted and burned or buried deeply.
• Keep fields free from weeds.
• Spray soap solution 2% and neem seed extract 3% for mealybug.
• Dipping setts of Dioscorea in 0.3% diazinon solution for Aphid.
• Resistant varieties are Kinabayo, Plimbite, Belep and Oriental and
florido.

15. Concentric leaf spot disease- S. rolfsi
• Okpala and Eziakor (1989) first reported the wilting of
yam vine caused by S. rolfsii in the eastern Nigeria.
• In 2002, the leaves of D. alata growing in farmer's
fields in the Pathanamthitta district of Kerala, showed
black, circular, concentric spots of between 5 and 10
mm in diameter, in the middle and bottom portion of
the vines.

16. Symptoms
• Circular leaf spots of varying sizes that form
concentric rings. At maturity, the center of the leaf
spots contained sclerotia of the fungus. The lesion
may merge, together with the Center eventually
falling out due to necrosis.
@ndrs.org.uk

17. Dry rot - Botryodiplodia theobromae
Symptoms
Though vary with varying coloration depending on the invading pathogen,
infected tissues become hard and dry. The infected tubers first turned grey and
then black, such tubers become pulverulent, breaking into small dry particles.
In case of Fusarium inducing pinkish with yelowish border on the infected
tissues.
@flickr.com

18. Pathogen
Inside the pycnidia, conidiogenous cells produce
hyaline thin walled pycnidiospores which become
brown, thick walled, two celled with longitudinal
striations.
Mode of spread
Primary spread and secondary spread is through air
borne conidia

19. Management
• After planting of yam sets may be dipped in ash
solution and air dried before planting.
• Fungal incidences can also be controlled by a proper
crop rotation.
• Treating tubers with hot water for 40 min at 50-55° C
before sowing and after harvest to reduce disease
both in field and storage

20. References
• Singh R.S., Diseases of Vegetable crops, third edition 2016, oxford
publishers, New Delhi, P.No. 374-375.
• Singh S.J., Virus and Phytoplasma Diseases of Vegetable Crops in India,
2004, kalyani publishers, New Delhi, P.No, 169-170.
• Saha L.R., Handbook of plant Diseases, 2002, kalyani publishers, New
Delhi, P.No, 398.
• Thind, T.S., Diseases of Fruits and Vegetables and their Management,
Kalyani publishers, 2001,P.No. 121-122.
• www.lsuagcenter.com.