Yam mild mosaic virus disease (530)

Pacific Pests, Pathogens, Weeds & Pesticides - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Yam mild mosaic virus disease (530)

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Photo 1. Indistinct, blotchy mosaic symptom on a leaf of greater yam, Dioscora alata.

Photo 2. Indistinct, blotchy mosaic symptom on a leaf of greater yam, Dioscora alata.

Photo 3. Abnormally long, deformed leaves on greater yam, Dioscoria alata from infection by Yam mild mosaic virus. The stringiness of leaves and vines to the left of centre is referred to as a 'shoe-lace' symptom.

Summary

Widespread. Present wherever Dioscorea alata and other species is grown.
Impact unknown. Caused by Yam mild mosaic virus, second most important after Yam mosaic virus disease (see Fact Sheet no. 526). Symptoms vary: leaves with mild yellowing, yellow and green spots, mottles and mosaics, severe leaf distortions and stunting.
Spread: aphids by flight and on the wind. Transmission in non-persistent manner - aphids acquire YMMV quickly, transmit it over next few hours, then lose ability to infect. Spreads also in sets for propagation.
Biosecurity: risk from unofficial introductions, trade in yams, and possibility of different strains.. Official movement of germplasm should always follow the FAO/IPBGR Technical Guidelines.
Biocontrol: none.
Cultural control: choose only healthy (often largest) tubers for sets; rogue plants that show early symptoms to prevent them being used as sets next season. Weed to remove infestations of aphids; collect and destroy or eat undersized tubers at harvest. Resistant lines may be available through international breeding programs.
Chemical control: not appropriate for this disease.

Common Name

Yam mild mosaic

Scientific Name

Yam mild mosaic virus; previously known as Dioscora alata virus, Yam virus 1. The virus belongs to the genus Potyvirus. The particles are flexuous rods. It is likely that there are two related groups of YMMV, one from Africa and the other from Southeast Asia, sharing a common ancestor. The abbreviation of the virus is YMMV.

Photo 4. Yam mild mosaic symptom on Chinese yam, Dioscorea esculenta.

AUTHOR Grahame Jackson
Information from Kenyon L, et al. (2001) An overview of viruses infecting Dioscorea yams in Sub-Saharan Africa. In: Proceedings of a conference on Plant Virology in Sub Saharan Africa, 4-8 June 2001, Ibadan, Nigeria.(https://www.researchgate.net/publication/216088409_An_overview_of_viruses_infecting_Dioscorea_yams_in_Sub-Saharan_Africa); Brunt AA, et al. (eds) (1989) FAO/IBPGR Technical Guidelines for the Safe Movement of Yam Germplasm. Food and Agriculture Organization of the United Nations, Rome/International Board for Plant Genetic Resources, Rome. (http://ecoport.org/Resources/Refs/IPGRI/yam.pdf); and Naidu RA, Hughes JDA (2003) Methods for the detection of plant virus diseases. In: Proceedings of a conference on Plant Virology in Sub Saharan Africa, 4-8 June 2001, Ibadan, Nigeria, (pp. 233-253). (https://cgspace.cgiar.org/handle/10568/96508); and Luo GF, et al. (2021) A review of viruses infecting yam (Disoscoea spp): implications for safe exchange of Pacific yam germplasm. Viruses 13; and Yam mild mosaic virus (2021) Crop Protection Compendium. CABI. (https://www.cabi.org/cpc/datasheet/19292); and Umber M, et al. (2020) Molecular virus diagnostics and sanitation of yam genetic resources: Implications for safe yam germplasm exchange. Viruses 12: 1101. (https://www.mdpi.com/1999-4915/12/10/1101); and Lopes-Montes A, et al. (2012) Yam breeding at IITA: achievements, challenges, and prospects. Research for development review. (https://biblio1.iita.org/bitstream/handle/20.500.12478/1579/U12ArtLopezmontesYamNothomNodev.pdf?sequence=1&isAllowed=y /).; and from Diouf MB, et al. (2022) Viruses of Yams (Dioscorea spp.): Current Gaps in Knowledge and Future Research Directions to Improve Disease Management. Viruses 14: 1884. (https://doi.org/10.3390/v14091884).

Produced with support from the Australia Centre for International Agricultural Research under project HORT/2016/185: Responding to emerging pest and disease threats to horticulture in the Pacific islands, implemented by the University of Queensland, in association with the Pacific Community.

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