SeedQuest | Mobile App

New host for Lethal necrosis on millet in Kenya

A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: July 2015
Source: Plant Disease [edited]
<http://apsjournals.apsnet.org/doi/full/10.1094/PDIS-10-14-1048-PDN>

[Ref: ES Kusia et al (2015): First Report of Lethal Necrosis Disease Associated With Co-Infection of Finger Millet With _Maize chlorotic mottle virus_ and _Sugarcane mosaic virus_ in Kenya. Plant Disease 2015; 99(6): 899; doi: 10.1094/PDIS-10-14-1048-PDN]

----------------------------------------------------------------------

Finger millet, _Eleusine coracana_, is an indigenous staple crop in eastern Africa mainly grown by smallholder farmers in rotation or side-by-side with maize. In 2011, maize lethal necrosis (MLN) was reported from Kenya [ProMED-mail post 20120117.1012452] as a result of coinfection with _Maize chlorotic mottle virus_ (MCMV) and _Sugarcane mosaic virus_ (SCMV).

During a survey for alternate hosts of MCMV and SCMV in MLN hotspots, finger millets with virus symptoms were sampled. Symptoms included chlorotic mottle from the base of young leaf whorls upward to the tips, and necrosis from leaf margins to the midrib. Aphids (_Rhopalosiphum_ sp., _Sitobion avenae_) and corn thrips (_Frankliniella williamsi_), known vectors of SCMV and MCMV, respectively, were identified.

Using DAS-ELISA, out of 20 samples 8 tested positive for MCMV and 5 for SCMV. 3 samples had both viruses and showed symptoms of necrosis similar to those in maize. ELISA results were verified by RT-PCR. PCR product sequences of MCMV-finger millet isolates were 100 per cent identical to [maize isolates] from Kenya; 98 to 99 per cent to isolates from DR Congo, China, and Taiwan; and 96 per cent identical to isolates from Nebraska [USA]. SCMV-finger millet isolates were 96 to 99 per cent identical to different SCMV [maize] isolates from Kenya. The 3'UTR sequences of [Kenyan] SCMV [isolates] had a 21 nucleotide deletion, which is only observed in a few other SCMV sequences worldwide.

To our knowledge, this is the 1st report on occurrence of lethal necrosis in finger millet from Kenya or elsewhere. The transmission of MCMV and SCMV from finger millet to maize or other hosts remains to be investigated and considered in management programs for lethal necrosis.

Communicated by: ProMED-mail <promed@promedmail.org>

[Maize lethal necrosis (MLN) is caused by co-infection of _Maize chlorotic mottle virus_ (MCMV, genus _Machlomovirus_, transmitted by chrysomelid beetles) with one of several other species of the family _Potyviridae_. MLN as well as MCMV were reported for the 1st time in Africa from Kenya in 2012 (ProMED-mail post 20130123.1510727) and the disease is spreading in the region.

As synergistic partners of MCMV in MLN, _Wheat streak mosaic virus_ (WSMV, genus _Tritimovirus_) or _Maize dwarf mosaic virus_ (MDMV, genus _Potyvirus_) had been reported previously from the Americas and Europe. _Sugarcane mosaic virus_ (SCMV) has been reported as the co-infecting virus in Kenya, but MDMV and SCMV belong to a complex of closely related potyviruses infecting tropical grasses. Based on serology, some strains (for example, MDMV-B) varying in host range and ability to be seed transmitted have been reassigned between the species which has resulted in some confusion in taxonomy.

Symptoms of the individual viruses are synergistically enhanced in MLN and may include leaf mottling and necrosis, distortion of ears, absence of kernels, failure to produce tassels, as well as stunting, premature aging and death of plants. Symptoms may disappear during the growing season leaving plants with latent infections but reduced yield as virus reservoirs and making disease monitoring difficult.

Infectious vector insects may be carried by wind over long distances.

Disease management may include crop rotation, certified clean seeds, control of vector species and weedy reservoir hosts, as well as use of crop cultivars or hybrids with reduced sensitivity to the viruses.

MLN resistance breeding has been set up in Kenya for maize. In the meantime, millets were amongst alternative crops recommended for MLN affected areas which makes discovery of the disease in these crops most unfortunate.

Maps

Kenya (with counties):

<http://www.guide2kenya.com/uploads/content/Kenya-County-Map.jpg> and <http://healthmap.org/promed/p/174>

Africa, overview:

<http://worldatlas.com/webimage/countrys/africa/maps/africa.htm>

Pictures

Maize lethal necrosis:

<http://cabiplantwise.files.wordpress.com/2013/04/maize-lethal-necrosis.jpg>,

<http://1.bp.blogspot.com/-8DVgQ8JnqQw/UBv0MFhAGQI/AAAAAAAAAAc/QrawWiKF06o/s1600/Maize.JPG>,

and

<http://westfm.co.ke/userfiles/images/Farming/MAIZE%20FARMING/Infected%20maize/Infected%20maize.jpg>

Symptoms of MCMV, SCMV and MDMV single infections in maize via: