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25 Aug 2017 Multiple pathogens, seed yam - Nigeria

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Published Date: 2017-08-25 04:30:43
Subject: PRO/PL> Multiple pathogens, seed yam - Nigeria
Archive Number: 20170825.5273274
MULTIPLE PATHOGENS, SEED YAM - NIGERIA
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Date: Fri 18 Aug 2017
Source: SciTech Africa [edited]
https://scitechafrica.com/tag/seed-yam/


According to the United Nations' Food and Agriculture Organization [FAO], Nigeria's yam yield has presently dropped to its lowest level in 2 decades, even though the area under cultivation is rapidly rising. Nigeria accounts for 61 per cent of yam production in the world.

"Seed yam is a big problem," said Robert Aseidu, International Institute of Tropical Agriculture (IITA). "It's only now that we're seeing how big a problem this could become." Due to many years of flawed farm practice, most seed yams have disease. Farmers traditionally keep back the measlier [poorer. - Mod.SH] yams for planting. "They keep accumulating diseases and productivity keeps reducing until you get to a stage where it's no [longer] economical to plant," says Beatrice Aighewi, IITA.

Some scientists have seen the urgent need and high demand for disease free seed yams. Aighewi says the solution to Nigeria's seed yam crisis is large-scale aeroponic seed yam production. She also produces high-yielding and disease-resistant yam varieties.

[byline: Uwagbale Edward-Ekpu]

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[Yam (_Dioscorea_ spp.) is an important tuber crop in Africa, the West Indies and parts of Asia and southern America. A number of fungal (anthracnose, leaf blight, tuber rots), bacterial (pre- and post-harvest wet rots), viral (mosaic, 'shoe-string') and nematode (dry rot) diseases or disease complexes are known to affect the crop. Many of these have been reported from West Africa, including Nigeria (see links below).

For predominantly vegetatively propagated crops, including root and tuber crops like yam, potato, taro and cassava, accumulation of multiple viral and other pathogens over successive planting cycles is a high risk. Even low levels of seed tuber infections pose a major risk of both horizontal and vertical pathogen spread. A build up of both numbers and individual levels of pathogens over the planting cycles will eventually lead to weaker and weaker crops, as described above for yams. To return to viable crop production, exclusive use of planting material that was certified, preferably by molecular methods, as being free of pathogens is essential for each crop cycle.

Farm saved or other uncertified propagating materials (including seeds, budwood, rootstocks, seed tubers, cuttings) have often been reported as sources of crop disease outbreaks worldwide. Clean planting stock is vital for successful agricultural systems and, consequently, certification schemes have been set up for relevant crops in many countries.

In aeroponic systems, as mentioned above, plants are grown in a mist environment, without a medium to support their roots. This differs from hydroponics, where plant roots are immersed in a liquid nutrient solution. In both systems, disease (and pest) control is aided by the absence of soil and minimal requirements for handling the plants during growth.

Maps
Nigeria:
https://i.infopls.com/images/mnigeria.gif
Africa (overview):
http://www.lib.utexas.edu/maps/africa/africa_pol97.jpg

Pictures
Symptoms of some yam diseases:
https://image.slidesharecdn.com/yam-151018121825-lva1-app6891/95/yam-20-638.jpg?cb=1445170831
Yam, genetic collection (Vanuatu):
http://farm4.staticflickr.com/3080/3105207130_45937822a4_z.jpg

Links
Additional news story:
http://www.npr.org/sections/thesalt/2017/06/26/533985373/scientists-try-to-break-nigerias-cycle-of-replanting-bad-yams
Information on some yam diseases via:
http://www.infonet-biovision.org/PlantHealth/Crops/Yam,
https://plantvillage.org/topics/yams/infos,
http://www.istrc.org/images/Documents/Symposiums/Seventh/7th_symposium_proceedings_0030.pdf,
http://www.pestnet.org/Home/SearchResults.aspx?q=yam and
http://r4dreview.iita.org/index.php/2015/03/20/continuing-viral-disease-threats-to-yam-in-west-africa/
Yam diseases in Nigeria:
https://www.ajol.info/index.php/ajb/article/view/14878,
http://www.tandfonline.com/doi/abs/10.1080/09670877809414142 and
http://agriculturenigeria.com/farming-production/pests-and-diseases
Yam crop information:
http://www.fao.org/docrep/x5415e/x5415e01.htm#1.4.2%20yams%20%28dioscorea%20spp.%29 and
http://www.croptrust.org/content/yam
FAO:
http://www.fao.org/
IITA:
http://www.iita.org/
- Mod.DHA]

See Also

Crop diseases - Philippines: (Cordilleras region) survey 20170718.5185031
Meloidogyne enterolobii root knot, yam - Nigeria: 1st rep 20170706.5154581
2015
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Leaf blight, taro - Nigeria: (KT) 20151119.3805332
2014
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Anthracnose, yam - Vanuatu 20140428.2434088
2010 
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Anthracnose, yam - Philippines 20100201.0343
2008 
---
Cucumber mosaic virus, yams - West Africa 20080505.1533
Anthracnose, yam - Nigeria: (Anambra, Enugu) 20080326.1128
2007 
---
Dioscorea mosaic virus, yam - Guadeloupe: 1st report, new potyvirus 20070712.2222
2006 
---
Anthracnose, yam - Jamaica 20060210.0443
2001 
---
Yam mild mosaic virus, yam - Colombia 20011003.2396
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