Diseases of elephant foot yam

1. DISEASES OF ELEPHANT FOOT YAM
STUDENT COURSE TEACHER
Miss. SNEHA R Dr. PARTHASARATHY S
ID. NO. 2015021120. Asst. Professor (Plant Pathology)

2. 1. Leaf blight - Phytophthora colocasiae
2. Collar rot - Sclerotium rolfsii
3. Dasheen mosaic virus - Dasheen mosaic virus (DsMV, a potyvirus)

3.  Scientific Name - Phytophthora colocasiae
 International Common Names
English : Blight of dasheen,
Leaf blight of colocasia spp,
Leaf blight of gabi,
Phytophthora leaf blight,
French : flétrissure des feuilles de taro
China : yu yi ping

4. Domain : Eukaryota
Kingdom : Chromista
Phylum : Oomycota
Class : Oomycetes
Order : Peronosporales
Family : Peronosporaceae
Genus : Phytophthora
Species : Phytophthora colocasiae

5.  Deciduous sporangia with apical papilla are
produced on slender sporangiophores which branch
irregularly or sympodially with a swelling at the
point of branching.
 Chlamydospores are thick-walled, usually 26-30 µm
diameter. Oospores averaging 29 µm diameter are
produced in oogonia with amphigynous antheridia
attached (Waterhouse, 1963; Stamps et al., 1990).

6.  Sex organs of individual isolates can be produced on
polycarbonate membranes stimulated by sex
hormones produced by the opposite mating type of
P. colocasiae or a different species of Phytophthora
(Ko, 1988).

7.  P. colocasiae occurs in South-East Asia, its probable area of
origin.
 It occurs in Indonesia
 China
 India
 The Philippines
 Malaysia
 Hawaii
 Papua New Guinea
 British Solomon Islands
 The Trust Territories of the Pacific

8.  The diseases appears in the form of small dark,
roundish spot on the leaf.
 The spot rapidly enlarge, coalesce and become
circular and the entire leaf dies.
 Drops of yellow liquid ooze out from the affected
areas.

9.  After harvest, grey-brown to dark-blue lesions occur
on undamaged corms.
 These lesions enlarge rapidly and coalesce.
 The boundary between the healthy and diseased
tissues is usually indistinct and soft.
 Affected corms are almost completely decayed at 8
days after harvest in wet conditions.

10. @icar.in
Symptoms

11. www.ndrs.org.uk

12. Life cycle
 Hyphae of the fungus generally survive longer in sterilized
soil (30 days) than in natural soil (5 days).
 At >20°C and >55% soil moisture the hyphae disappeared
with 5 days of burial in natural soil (Sitansan Pan et al.,
1994).
 Thus it is assumed that where the crop is seasonal the fungus
survives as mycelium within stored corms used as
propagating material for the next season's planting.

13.  Free water is needed for sporangial germination and
zoospore mobility.
 Close to 100% RH is needed for infection to occur.
 At optimal temperatures of 24-27°C.
 sporangial germination, release of zoospores and
penetration occur after 6-8 hours.
 The fungus enters the plant through the cuticle and a
latent period requires 2-4 days at optimal
temperatures of 27-30°C.
 In wet weather the lesions of infected leaves or
petioles may produce many sporangia and zoospores
are disseminated by rain splash.

14.  P. colocasiae occurs under conditions of high
temperature and humidity, in wet areas and densely
planted fields.
 Epidemics occur frequently between July and
September in Hainan, China.
 Primary leaf infection has been observed following
tropical storms.

15.  This disease can lead to a 30-40% crop loss in
heavily infected taro fields (Jackson et al., 1975).
 The fungus is widespread in South-East Asia and
parts of Oceania, where it causes severe leaf damage
and considerable loss of corm yield.

16.  In the Philippines, yield reductions ranged from 24.4%
in resistant to 36.5% in susceptible cultivars (Vasguez,
1990).
 The fungus is capable of infecting undamaged corm
tissues under conditions of high humidity resulting in
severe corm decay in the storage stage.

17. Cultural Control
 Cultural practices towards disease control include
minimizing the source of inoculum.
 Use of disease-free plant material.
 Roguing infected leaves.
 Avoiding excessive levels of moisture.

18.  Fungicidal control is largely practised against P. colocasiae
in taro cultivation.
 Currently widely used products are) systemic (metalaxyl and
non-systemic fungicides (copper oxychloride, mancozeb,
zineb) applied as foliar sprays.
 In India spraying metalaxyl at intervals of 15 days was
effective in controlling the disease under field conditions .
 Good control was obtained with metalaxyl and fair control
with copper oxychloride (Aggarwal et al., 1987).

19. Cont….
 Applications of mancozeb at 7-day intervals gave substantial
disease control and increased yields in Hawaii.
 But in the Solomon Islands mancozeb did not control the
disease or increase corm yields, while mist-blower
application of copper oxychloride gave effective control of
P. colocasiae and increased corm yield (Jackson et al., 1989).

20. Introduction
 Collar rot is most common disease, and prevalent in all
Amarphophallus growing areas.
 This diseaes occurs in serious from if the clay content is
more in the soil.
 It is caused by Sclerotium rolfsii Sacc.
 Sclerotium rolfsii Sacc. is being well known
polyphagous, ubiquitous omnivorous and most
destructive soil borne fungus.
 This was first time reported by Rolfs (1892) as a cause
of tomato blight in Florida.

21. Kingdom : Fungi
Phylum :Basidiomycota
Class :Agaricomycetes
Order :Agaricales
Family :Typhulaceae
Genus :Sclerotium
Species :S. rolfsii

22.  The pathogen, Sclerotium rolfsii Sacc. is distributed
in tropical and subtropical regions of the world
where high temperature prevail.
Host Plants
 The fungus has a wide host range of 500 species in
about 100 families including groundnut, green bean,
lima bean, onion, garden bean, potato, sweet potato
and water melon (Aycock 1959).

23.  The pathogen attacks the collar region and produces
water soaked lesions.
 The whole plant soon turn yellow.
 The stem shrinks and collapses due to rotting.
 Water logging, poor drainage and mechanical injury
at collar region favour the disease incidence.

24.  Brownish lesions first occur on collar regions,
which spreads to the entire pseudo stem and cause
complete yellowing of the plant.
 In severe case, the plant collapses leading to
complete crop loss.

25. www.icar.in
Symptoms

26. link.springer.com

27. link.springer.com

29. Cultural Method
 Neem cake at 10 q/ha, mustard cake at 10 q/ha, karanj cake
at 10 q/ha, neem + karanj at 5 q/ha and T. harzianum pre-
colonized farmyard manure (FYM) at 2 t/ha were tested.
 The role of intercropping in the management of collar rot of
elephant foot yam. Using turmeric and ginger as intercrops.

30.  The efficacy of an integrated management strategy,
involving seed treatment with hexaconazole, soil
drenching with Vitavax [carboxin], soil application of
neem cake and FYM enriched with T. harzianum.
 Use disease free planting material, remove infected
plant materials, improve drainage conditions,
incorporate organic amendments like neem cake, drench
the soil with carbenilazim or apply biocontrol agents
like Trichoderma harzianum @ 2.5 kg/ha mixed with
50kg of FYM (lg/l of water).

31.  Dasheen mosaic virus (DsMV, a potyvirus)
Family : Potyviridae
Genus : Potyvirus
Species : Dasheen mosaic virus
Acronym : DsMV

32.  Appears to be world-wide, especially in tropical and
subtropical regions.
 Reported from the Caribbean Egypt, Florida, USA,
Europe, India, Japan and Oceania.

33.  Hosts of DsMV include important root and tuber
crops such as Alocasia, Colocasia and Xanthosoma,
and the ornamentals Caladium,
Dieffenbachia and Philodendron.

34.  Primary spread is through planting material.
 Secondary spread of the disease is through insect.

35.  Vectors: DSMV is transmitted by several species of aphids,
including the green peach aphid (Myzus persicae), the
cowpea aphid (Aphis craccivora), and the melon aphid
(Aphis gossypii). DsMV is not transmitted by the banana
aphid (Pentalonia nigronervosa) or by the bird cherry-oat
aphid (Rhopalosiphum padi).

36.  The virus is transmitted in a non-persistent manner
 Vegetatively: by suckers, corms, or infected cuttings used
for propagation.
 Mechanically: by plant sap on knives or shears (yet DsMV is
not transmitted by incidental contact or natural rubbing of
leaves between plants).
 Note: DsMV is not transmitted by seed or by pollen.

37. Dispersal:
 DsMV is dispersed by several species of aphids, by the
movement of infected plants; as infected plant sap on
pruning tools.
Inoculation:
 DsMV arrives at the site of infection (a wounded plant
cell) in an aphid’s mouthparts or on an infested cutting
tool.

38. Infection:
 DsMV enters a wounded plant cell either by aphid
injection or on an infested tool.
Disease development:
 Virus particles multiply within plant host cells,
eventually resulting in symptom development. Virus
particles move between adjacent cells via
plasmodesmata and long-distance within a plant via the
vascular tissues.
Pathogen reproduction:
 The virus particles replicate by usurping the plant cell’s
DNA and protein-synthesizing capacities.

39.  Disease symptoms include mosaic mottling of
leaves and distortion of leaf lamina.
 Corms produced by the mottled plants are much
smaller than those without mottled leaves.

40. Researchgate.net

41. Researchgate.net

42. www.ccari.res.in

43.  Avoid introduction or transmission of the virus during
vegetative propagation.
 Prevent the introduction and spread of this disease on
new hosts.
 Control aphids and ants where aphid transmission of
DsMV is a problem.
 Use of virus free planting material, spraying of systemic
insecticides to prevent secondary spread.