Diseases of elephant foot yam

Diseases of elephant foot yam

1. COLLEGE OF AGRICULTURAL TECHNOLOGY , THENI (Affiliated to Tamil Nadu Agricultural University, Coimbatore-3) Kullapuram (Po),Via Vaigai Dam, Theni-625 562 DISEASES OF ELEPHANT FOOT YAM STUDENT COURSE TEACHER Miss. SNEHA R Dr. PARTHASARATHY S ID. NO. 2015021120. Asst. Professor (Plant Pathology)

2. Elephant Foot Yam Diseases Leaf blight - Phytophthora colocasiae Collar rot - Sclerotium rolfsii Dasheen mosaic virus - Dasheen mosaic virus  ( DsMV , a potyvirus ) 

3. 1.Leaf blight 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. Systematic position Domain : Eukaryota Kingdom : Chromista Phylum : Oomycota Class : Oomycetes Order : Peronosporales Family : Peronosporaceae Genus : Phytophthora Species : Phytophthora colocasiae

5. Description 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. Cont… 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. Distribution 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. Leaf blight symptoms 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. Biology and Ecology 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. Epidemiology 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. Impact 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. Management 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. Chemical Control 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. 2.Collar rot 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 Systematic Position

22. Distribution 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.   Damage Symptoms

24. Cont… 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

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28. Life cycle

29. MANAGEMENT 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. 3.Dasheen mosaic virus  Dasheen mosaic virus  ( DsMV , a potyvirus )  Family :  Potyviridae Genus :  Potyvirus Species :  Dasheen mosaic virus Acronym : DsMV

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

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

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

35. DsMV is transmissible by three methods 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. Cont… 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. Disease cycle for dasheen mosaic 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. Cont… 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 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 leav e s. 

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42. www.ccari.res.in

43. Integrated Disease Management 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.